Synthesis of cell wall components: Aspects of control

003 l-9422/88 $3 00 + 0 00 Pergamon Press plc

Phytochennstry, Vol 27, No 5, pp 1235-1253, 1988 Pnnted m Great Brltam

REVIEW ARTICLE NUMBER 31 SYNTHESIS

OF CELL WALL COMPONENTS:

ASPECTS

OF CONTROL

G. PAUL BOLWELL* Department of Biochenustry, Royal Holloway and Bedford New College, University of London, Egham Hdl, Egham, Surrey TW20 OEX, U.K. (Receloed 24 July 1987)

Key Word Index-Plant pathogenesls

cell walls; membranes; synthesis, polysacchandes; wall-bound protems, phenohcs, development, stress,

Abstract-The dynamic qualities of the plant cell wall are explored. Recent developments in the understandmg of how membrane systems operate in the synthesis of wall components is discussed. Particular attention 1s paid to the synthesis of polysaccharldes and wall-bound phenolics, while the identification of some wall bound proteins and the subsequent study of their synthesis and processing is also descnb-ed. Probable molecular controls, both quahtatlve and quantitative, govermng the appearance of newly synthesized components wlthm the wall are discussed The conditions under whch sets of components are modified speafically, by the accumulation of newly synthesized material or extracellular enzyme action, are outlined Some deficiencies in understanding how these aspects may be interrelated, especially with regard to mechanisms of slgnal transduction are hlghlighted However the potentially rapid capacity for Implementation of changes m the extracellular matrix of the cell, probably commencing with processes of activation of specific subsets of genes m response to particular signals, is striking

INTRODUCTION The purpose of this review is to attempt to brmg together diverse observations on the dynamic qualities of the plant cell wall In general, the view of the cell wall 1s moving away from that of a passive extracellular matrix concerned with maintenance of shape and rigidity to that of a much more dynamic structure Thus, the plant cell wall undergoes profound changes during growth and development and in response to stress and pathogenesis, and may, as a source of Information, be intimately involved in self and non-self recognition processes. The latter aspects are perhaps not surprismg considering the existence of a complex laminated structure forming a series of potentially selective surfaces This review considers those underlying synthetic and modificational events initiated in response to a variety of signals which are fundamental to the expression of changes m this laminated matrix at the cellular level. There 1s a large body of studies appertaining to these areas but a considerable lack of understanding of the assembly of such a complex structure remains, although an attempt 1s made here to

Abbreviations. CAD, cmnamoyl alcohol dehydrogenase; CA4H, cmnamlc acid 4-hydroxylase, 4CL, 4-hydroxycmnamlc acid-CoA hgase, CHI, chalcone Isomerase; CHS, chalcone synthase; COMT, caffelc acid O-methyl transferase; HRGP, hydroxyprolme-nch glycoprotem, IAA, mdoleacetlc acid, NAA, naphthylacetlc aad, PAGE, polyacrylamlde gel electrophoresis; PAL, phenylalamne ammoma-lyase *Present address. Department of Blologlcal Saences, City of London Polytechmc, Old Castle Street, London, El 7NT, U K

outline where the impact of newer types of approaches might bring forth advances. Nevertheless, the problems involved in understanding the myriad of molecular recognition events involved in the synthesis and assembly of a ‘secondary’ structure such as the plant cell wall seem particularly dauntmg when one considers the astomshmg potential complexity of ‘primary’ gene expression [l], wlthout subsequent changes. Cell wall structure Although the detalled analysis of cell wall structure is beyond the scope of this review which 1s primarily concerned with synthesis of components, some comments about subsequent assembly and interrelationships are necessary. Considerable advances of course have taken place in the analysis of structural components generated by chemical or enzymatic means of extraction [2X]. These detailed studies have been largely confined to simpler primary walls and have served to classify the range of non-celluloslc polysaccharides. In one case, the 41 wall of the cultured sycamore cell, this has been accomplished to an extraordinarily sophisticated level. These methodologies have revealed the range of linkages and m some cases partial sequences in the primary structures, branched and unbranched, in the more complex polysaccharides. These are now accepted for the maJor components. However, there is much controversy about the nature of the interactlons and assoclatlons of polysaccharides and proteinaceous components in the non-hgmfied wall which m part resides m an adherence to tradltlonal classifications based on methodologies of extractlon It 1s important to ascertam whether the

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1136

G P

heterogenetttes observed m the analysts of Isolated matertal wtthm the broad types of polysaccharrde and then associated molecules 1s indrcattve of the true range found zn IVVO It may be that tradtttonal analyttcal procedures arc Inadequate to answer these questions completely and that complementary studies of the brosynthettc machmcry, as regards the full range of enzymatic specrfictty, however redundant or spatrally or temporartly separated tt may be, may hold many of the answers At least, studies at thts btosynthetrc level, which may mclude polysaccharides m the process of secretton, do not have the added complextttes due to assocrattons generated by the formatton of addtttonal bonds extracellularly or even during tsolatton Many of these extracellular cross-linkages between mdtvldual components have been examined usmg parttal enzyme degradations [669] Nevertheless, although early theorettcal attempts incorporated the observed range of secondary lmkages, models for the assocrattons of mdrvtdual components wrth known primary structures have met with hmtted success Newer elegant studies using ultrastructural locahzatton with lectms and enzymes [IO- 121 and polyclonal and monoclonal anttbodies [ 13 ~151should bring about rapid tmprovements of our understanding m thts area When used m combrnation, such as m utthzmg different-sized collordal gold partrcles to localize separate components dtstmgutshed by spectes-specific anttbodres or other mteractmg proteins, important mformatton on the assocrattons found wtthrn the matrix and during wall assembly should become apparent and complement tradrttonal htstochemrcal, autoradtographtc and electronmrcroscoptc methods [l&19] The excttmg prospect remains for the deveiopment of probes for the synthetic components (cDNAs and antibodies) and for then cell wall products (antrbodies and htstochemlcal agents) to visualize changes at the level of single cells using m srttr hybrtdizatton and cytochemtcai methodologtes These temporal mterrelationships of the component structures are even less studted since much of the detailed mformatron has been derived from primary walls The potential complexity of these processes IS highlighted when one considers that even wtthm a smgle cell such as a germinating Fucuc zygote, drstmct polysacchartde motettes are directed to different areas of the cell durmg rhtzotd development [20, 211 However, such directed deposttton IS begmnmg to be understood, as 1s subsequent assembly, with the recent demonstratton of the reassembly of Chlumydomonus glycoprotemaceous wall components rn txtro [22] Although stmrlar protems exist m higher plant cell walls, such in ultra studtes must be a long way off although uuttal attempts at reconstttutrons are being made [23] Faced wtth such complexrty, understandmg the synthesis and assembly of such a structure and Its subsequent modrficatton during growth and dtfferentratton or m response to envnonmental factors, would seem dauntmg However some constderable progress has been made. parttcularly m plant phenolic metabohsm This review deals wtth recent advances m understanding the syntheses of wall components, polysaccharrdes, proteins and phenohcs and mmal attempts to define the temporal and spattal controls operatmg With the input of tmmunological and molecular btologrcal techniques some of these changes m components can now be followed and thus open up the posstbthty of beginning to understand the molecular nature of the control systems

BOLWELL

Synthesis oj components GlycosyIutlon Unlike glycosyl transferases of ammal cell endoplasmrc reticulum and Golgr body [24-271, no plant glycosyl transferase of polysaccharrde synthase has been fully characterized at the molecular level. The reason partly resides u-t the dtfficulty expertenced m solubrhzmg and reconstttutmg the mdtvtdual enzyme systems that have been charactertsed so far Thus a number of alternative approaches have been designed for mdnect tdentdicatton of these elustve enzymes. Understandably most mterest has been drrected towards those systems synthestzmg homopolymers or those contammg simple repeated units For the more complex polysacchartdes, the possrbthtres of complex precursors, block synthesis or partially redundant enzyme spectficrty has to be taken Into account when exammmg the mteractron of the synthetic systems However some progress has been made m developmg condttrons which lead to solubthzatton of polysacchartde synthases as a prereqmstte for purtticatton and molecular tdenttficatton Interestmgly Trtton X-100 has been found to be most efficient at solubthzmg activity although recoveries are mvartably low Other detergents, often considered to represent milder condmon have not been employed to such success and tt IS mterestmg to speculate whether the greater mtcelle size generated by Trtton X100 may have a stgmfcant effect m mcorporatmg addtttonal membrane bound factors The polysacchartde synthases appear to have K,s In the FM range and stmtlar requirements for Mg’ + and/or Mn” i. w htle tt IS thought mtermedrate transfers mvolvmg hptd glycostdes are not mvolved [28--301 This IS m contrast to the sttuatton involved m protein glycosylatrons, some of the products of which are targetted mto the wall, where m common wtth similar glycosylatrons m animal cells hptd mtermediates are mvolved [31-331 In particular the followmg glycosyl transferases have been described

Glucans The identity of cellulose synthase has been a matter of constderable debate for some time Partly contrtbutmg 1s the failure to achieve accurate and substantral synthesis of p(1-t4) linkdges from UDP- or GDPglucose precursors wtth membrane or parttally reconstttuted preparations as a prerequisite for purdicatton This IS exemphfied by one report [34] of rates of cellulose synthesis m two approaching that found zn CICOthat wds later qualified The problems experienced m achieving /j (1+4) glucan synthesis reflect the dtfficulty m preparing, for possrble reasons discussed below, higher plant plasmalemma. which are uncontammated wtth endomembranes capable of other glycosylattons Perturbanon of membrane integrity also appears to activate the formatton of/j (I ‘3) lmkages which may be catalysed by the same enzyme or part of the cellulose synthase complex [35-381 Smce It IS anttctpated that a molecular tdentdication of/J (1+3) glucan synthase or callose synthase wtll be achieved soon [39-411 tt may mdnectly lead to the characterrsatton of cellulose synthase. The theory behind the equtvalence of these acttvtttes has been expounded most eloquently [42] and IS based on a number of prevtous observations [3%38, 43, 443 The tdenttty WIII probably be confirmed by those attempts to tdenttfy cellulose synthase by indirect methods so far employed including electrophorettc methods [4S 473, acttve-stte-

Synthesis

of cell wall components.

directed labelling [45, 48, 491 and radiation bombardment inactivation [SO] Polypeptldes so far identified as good candidates are an M, 68 000 polypeptlde from red beet [47,50]; or three of M, 18 000,43 000 or 73 000 from mung bean [45,48] although the 73000 has recently been thought to be involved in transport and the 43000 may represent a glycoprotem since the label appears to be covalently bound [Read, S. M., personal communication] The 18000 polypeptide may possibly have some regulatory function. At present, without ldentlficatlon of the enzyme, it is not known whether the changes m enzyme activity that have been observed m several systems [51-541 have their underlying basis m the amount of enzyme present and ultimately gene regulation Synthases mvolved rn hemrcellulose synthesis Among those already described in which the product has been identified to an appreciable extent include synrhases involved m xylan, xyloglucan, glucuronoxylan and glucomannan synthesis. Xylan synthases catalysmg homopolymer fl (l-+4) xylose linkages have been described from corn [SS], mung bean [56], sycamore [57] and French bean [58] and appear similar as regards cofactor requirements. Attempts to solubihze these enzymes lead to low recovery for the sycamore enzyme [57] and for the bean enzyme (Bolwell, G. P., unpublished results) making further purification difficult. Xyloglucan synthesis by membrane preparations from pea [59-621, suspension cultured soybean cells [63-671 and bean cells [68] has been described although the mechanism of the concerted enzyme activities 1s unclear [69] The question as to whether side chain zesldues are added to preformed backbone or during growth of the heteropolymer chain 1s also unresolved for the interaction of glucuronyl- and xylosyl-transferases mvolved m glucuronoxylan synthesis catalysed by membrane preparations from pea eplcotyls [69, 701 Similar questions also arise during glucomannan synthesis which has been described m membrane preparations from Phaseolus aureus, pea and Pmus sylvestrrs [71-781. For the heteropolysaccharldes, available evidence points towards a concerted synthesis at the site of the growing chain perhaps by multienzyme complexes. The fact that side chain synthesis cannot be brought about by the addition of primers makes an alternative mechanism of addition to a preformed backbone unlikely, while despite extensive searches for intermediates, the demonstration of block synthesis vta perhaps lipid-linked precursors has been largely ruled out [28-30,691 Complex ohgosaccharldes linked to lipid donors have been demonstrated but do not have the relevant block structure; these appear to be involved m protein glycosylatlons and are discussed below. Synthases mvolved in pectx polysaccharide synthesrs. Homogalacturonon synthesis has been studied m mung bean [79] sycamore [SO] and pea [Sl] No mformatlon is available on rhamnogalacturonan synthesis or the dauntingly complex minor substituted rhamnogalacturonan-based wall components whose structure has been worked out so elegantly Arabman synthesis has been described for membranes from mung [56] and French bean [58] In the latter case use of a monoclonal antibody lead to a prehmmary ldentlficatlon of the arabman synthase as an M, 70000 polypeptide [82] Other transferases have been described that are mvolved m either backbone or side chain elaboration. Some of these are involved m protein glycosylation but

aspects of control

1237

might also be involved m polysaccharide synthesis. These mclude galactosyl transferases [83-851 and fucosyltransferases [86-881 However, the fucosyl-transferase from Fucus 1s known to be involved m homopolymer fucan synthesis, while another described in pea 1s involved in fucosylatlon of a preformed xyloglucan nonasaccharlde

C891

Glycosyl transferuses in protem glycosylatrons. Conslderable progress is now being made m understanding protem glycosylatlon some of the products of which will be targetted mto the wail. Followmg the pioneering work m non-animal systems especially yeast [32,90,91] the basic gluNAc,-man,glc, core ohgosaccharide N-linked to peptide-asparagme so elegantly worked out m animal cells [24, 251 has been demonstrated m plants [92, 933. This type of glycosylation and subsequent processing, where this 1s permissible depending on conformatlonal constraints [94], is now well understood for membrane preparations from French bean [33, 95-991, mung or soybean [100-l 031. Although there 1s some debate about a role for glycosylated domains, possible mvolvement m sorting of newly synthesized proteins for secretion mto the wall is an attractive possibility. However glycosylatlon 1s not a requirement for the transport of phytohaemagglutmm and P-fructosldase [104, 1051. It therefore still remains a challenge to understand how N-linked glycoprotems such as phaseolhn and phytohaemogglutimn are targeted mto protein bodies while peroxldases, for example, are directed to the wall Molecular mvestigations currently implicate multiple recognition sites based on secondary and tertiary structures at the N- and perhaps C-termim Monoclonal antibodies to glycosylated domains may enable further mvestlgations, a multlantlgemc oligosaccharlde site on secreted proteins has been identified [MacManus, M., personal commumcation] which may represent a particular processed ohgosaccharlde motif Q-linked glycosylatlons are less understood. Evidence for the mvolvement of pentosyl-lipid intermediates has been obtained [ 106,107] but these may not be obligatory [lOS-1101 O-linked glycosylatlons are also found m secreted products, e.g. threomne- and serine-linked oligosaccharides of maize-root slime [ 111, 1121 or serme- and hydroxyproline-linked ohgosaccharldes of wall-bound proteins Membrane preparations capable of carrying out such glycosylations have been described [106-l 121 for a number of sugar precursors Fme control of polysaccharlde synthesu. As discussed below evidence suggests the major controlling factor in the qualitative production of polysaccharides resides in the complement of synthases found at any one time m the endomembrane system. However the avallablhty of nucleoslde diphosphate sugars appears to be under some fine control through a feed-back mhlbltion of UDPglucose dehydrogenase by the level of UDP-xylose [ 1131 This mechanism probably acts to restrict the accumulation of sugar nucleotldes although it can be bypassed by the mosltol pathway [ 1141 There 1s httle information on the respective regulation of these alternative pathways. The levels of nucleoslde dlphosphate sugars appear not to be limiting to any great extent [113, 115, 1161 probably since the levels of enzymes mvolved m the interconversions, UDP-glucose dehydrogenase and decarboxylase and the eplmerases, appear to be maintained [ 113, 117, 1181 There 1s little or no direct evidence for fine control mechanisms at the level of the synthases

1238

G P BOLWELL

except for a modulation of a xylan synthase by nucleoside mono- and dlphosphates [ 1131and the complex and as yet not unequlvocably demonstrated modulation of cellulose synthase [39, 421. The latter may be directly related to the regulation of callose synthesis dtscussed m another context below [41, 1191 Proterm Strwturul

protem Although there have been consldernble advances m the Identdicatlon and structural characterlzatlon of hydroxyprolme-rich glycoprotems, other aspects, mcludmg their blologlcal role, remam obscure Nevertheless. there IS ample circumstantial evidence for a fundamental role m cell wall structure and disease reslstance although confirmation awaits more direct evldence, perhaps employmg transformation systems and antisense-RNA technology This IS now possible with the ldentlficatlon and clonmg ofgenes encodlng prolme-rich precursors from a number of sources [120- 1221 Sequences currently available encode ‘extensm’ HRGPs but It has become apparent that a number of other precursors undergo peptlde-prolme hydroxylatlon and glycosylatlon before secretion mto the wall ‘These Include arabmogalactans 1122 1253, solanaceous lectms [ 122. 125,126] and others yet to be classified [107, 127, 1281 The full range of HRGPs has yet to be demonstrated and charactensatlon at the protein level has been difficult due to msolublhzatlon of HRGP precursors m the wall [129, 1301 Some progress has been made by lsolatmg precursors by salt elutlon from the wall [131L133] or at their site of synthesis wlthm the endomembrane system [ 128, 1341 As a result a number of HRGPs have been described These \ary m M, of the deglycosylated monomer, bemg m the range 3UOOO~55000, and with a hydroxyprolme content of between 6-50% Genes from a number of sources encoding extensm-like variants have been Identified and sequences are available [ 1221 These are characterized by repeated ammo acid sequences encoded by codons of restricted redundancy Comparative homologtes of HRGPs that are not of the extensm family are awaited, which will mcldentally give an mdlcatlon ofthe range of ammo acid sequences subjected to prolme hydroxylatron Recently. another class of proteins, probably wallbound, which are rich m glycme have been inferred both from ammo acid analyses of plant cell walls and from the sequence of a Perunra protem, has been described [135, 1361 These may replace HRGPs m some species It IS interesting to speculate whether both might have evolved from some of the common G/C rich portions of the genome where the codon frequencies CCX (pro) and GGX (gly) would be prevalent The range of prolme residues capable of bemg hydroxylated IS dependent on the speclficlty of the prolyl hydroxylase (EC 1 14 11 2 ) This 1s now a well characterized enzyme from a number of sources [l37--1401 The enzyme 15 tetramerlc having two active subumts with M, of 65000 (which may dissociate mto two polypeptldes of M, 32500 m the Vincc~ enzyme [141]) and two mactlve subunits of M, 60000 which do not copurlfy on affinity chromatography m the presence of dlthlothreltol [Robmson, D , personal commumcatlon]. In contrast. another report of the purlficatlon of the enzyme from C~~um~&monn,s ldentllies an M, 40000 protein [142] At this time the discrepancy over the Chlamydomonas enzyme 1s unresolved [140, 1421 An antibody raised against the M, 65 000 subunit from bean also cross-reacts

with a putative M, 60000 subunit [143] and also recogmses an M, 32000 polypeptlde from potato m Western blots [Bolwell, G P . unpublished results] The plant prolyl hydroxylase has very slmllar properties to the mammalian enzyme but differs m bemg capable of the hydroxylatlon of polyprolmc UT Lltro The vertebrate enzyme [144] consists of two active x subumts and two /I subunits whose cDNA sequence has close homology with a protein dlsulphrde lqomerase [145] suggesting a complex remarkably adapted to post translatlonal modlfications It IS not known whether the 6OUOOsubumt ofthe plant enzyme has a slmllar function AlternatIvely, the 60000 lsomerase may represent a separate protem (Hanauske-Abel. H , personal commumcatlon) The plant enzyme 1s associated with the endoplasmlc retlculum, but whether smooth or rough requires absolute confirmation [I37-1431. although bemg a Iummal protem [I461 It could possibly be found m both Hydroxyprolme resrdues dre also arabmosylated m extensm and aolanncrou~ lectms [ 1 12, 122, 125] while m the arabmogalactans the side chains are more complex [lZ, 1241 Ohgosaccharlde hplds pobslbly mvoived m Intermediate transfers have been described [83, 106, 1071 and transfer to endogenour polypeptldes has been demonstrated The serme residues of HRGPh arc galactosylated, a transferase which may cdtalyse this post translatIonal modlficatlon hdx been described [X3, 147s Enzymes A great number of enzymes thought to be wallbound have been described of uhrch haking particular relevance to this review are the hydrolases dnd peroxidases although other groups of enzymes Include proteases dnd phosphatases A numher of these actlvltles, due to technical dlflicultles In wail Iholatlon, require absolute confirmation of a wall locahzatlon. probably through lmmunologlcal techniques Pwo.xldase\ Peroxldases have long been famlllar components of plant membranes and ualls and h;l\e long been recogmsed as capable of brmgmg about mtermolecular cross-lmkmg of phenohc residues m the presence of hydrogen peroxide ‘Total celf peroxldase activity IS a product of a range of dlfferentl,lllq Induced and locahzed lsoenzymes [I48 1541 some of which ma) he wallbound Perovldases are also secreted from suspension cultured cells [ 155 1581 They form a very heterogenous group when analysed on the bawls of pl and M,. usually by hlstochemlcal stammg followmg gel electrophoresrs. Correlating such bands on gela to actlvlty 111uvo should be undertaken with caution as other haeme protems, such as cytochrome P450, and Cu’ ’ phenolases can exhibit peroxldase actlclty under certam circumstances The complete characterlaatlon of a wall-bound peroxldase at the molecular level IS antlclpated soon [cf 159.-1621 Hydrohes Plant cells can exhibit a large range of hydrolase actlvltles which are dependent on the tissue or mode of mductlon Thus the glycosldases Involved in seed germmatlon form an extensively characterlsed group [163, 1641 whrch have some relevance since some storage polysaccharldes are wall-bound and resemble the non-celluloslc polysaccharldes of primary and secondary celLwaIfs ofvegetative tissues Thus moblhsatlon of these storage matenals, e.g xyloglucans of the Legummosae. or of wall-material durmg fruit ripening or absclss:on may represent enzymatic mechamsms which may be responsible for cell-wall turnover at n much lower rate m vegetative tissues. itself a controversial issue unttl re-

Synthesis

of cell wall components.

cently Since the specific expression of genes encoding glycosidases occurs at a high level in some tissues this has attracted some interest recently leading to the characterisation of cellulases [165, 1663, b [l-3] glucanase [167-1691, chitmase [17&173], exo /3 [14] glucanase [61, 1741 and detection of activities of a and /J glycanases specific for the whole range of residues found in wall polysacchartdes Cl7551791 However, at the protein level tt has often not been established which of the hydrolases identified are actually secreted mto the wall, how active they are tn UIUO,or whether the products of their activity are mobilized to any great extent in intact vegetative tissues Spectfic products of the hydrolysis of wall polysaccharides can be readily demonstrated m suspension cultured cells however [ 180, 1811. Breaking of such covalent bonds may have important consequences for growth through wall loosenmg mechanisms Additionally, production of specific oligosaccharide fragments may of course have important consequences for cellular control mechanisms [182-1861. Similarly, proteases may be important m wall loosenmg Wall-bound protease activity has been demonstrated [187, 1883 Ligmn and phenohcs Enzymology and control of phenohc

metabohsm The pathway from L-phenylalanme through hydroxycmnamoyl intermediates provides substrates which converted to then coenzyme A thiol esters, serve as precursors which are channelled mto branch pathways leading to the btosynthesis of a number of classes of secondary products [189-1911 Many of the enzymes of the central phenylpropanoid pathway and the lignm and flavonotd branch pathways are now well characterized and then properties have been reviewed [192-1941 With the increasmg use of tmmunologtcal and molecular btologtcal approaches there have been considerable advances m our understanding recently Phenylalanme ammoma-lyase (PAL, E.C. 4 3.1 S.), the first enzyme of the phenylpropanoid pathway leading to the formation of hgnm, IS probably the most extensively studied enzyme of secondary metabolism and has been the subject of many reviews including one m this series [195] PAL from most sources appears to be a tetramertc enzyme possessmg two dehydroalanine-containing active sites per molecule The subunit M, appears dependent on the source and mode of purification but 1s usually in the range 7700&83000 for most species [19&199]. If analysed by chromatofocussmg, the enzyme from bean [200] or potato [Gtlliatt and Northcote, personal communication] can be resolved mto at least four forms of differing p1 and kinettc properties This suggests the negatively cooperative kinetics previously reported for PAL [201] may reflect combmed activities of the different forms with differing Mtchaeh-Menton properties. Molecular clonmg of cDNA encoding PAL has been described from parsley [202] and bean [203] and has lead to the tsolation and charactertsatton of three PAL genes from bean [204] With the wide availability of the cDNA clone tt is anticipated that PAL genes from a number of species will soon be characterized. However questions remam as to the association of the subunits and the true nature of the active site. Cmnamic acid 4-hydroxylase (CA4H, E.C.l. 14 13 ll), the second enzyme of the central phenylropanotd pathway is a cytochrome P450-dependent mixed function oxygenase [205,206] Other reactions m phenohc metabolism thought to be catalysed by cytochrome P45Os

aspects

of control

1239

include the S-hydroxylatton of ferulic acid [207] in phenylpropanoid metabolism and a number in isoflavonoid phytoalexin biosynthesis [208, 2091. As yet none of the proteins responsible for these activities has been identified unequivocably at the molecular level due to difficulties in purification and reconstitutton. However a P450 of M, 56000 capable of some reconstituted CA4H acttvity was isolated from Jerusalem artichoke [210] Another P450, possibly capable of CA4H acttvity, of M, 52000 had been identified m tuhp using homologous antibodies whtch dtd not cross-react with antigens from any other species [ZlO]. Similarly, heterologous antibodies to bacterial P450 dtd not cross-react with antigens from plant species [212] while a report of the tdenttficatton of a M, 48 000 polypepttde as a possible CA4H [144] using a cross reactive anti-rat P450 monoclonal antibody may have been premature due to the semi-specific behavtour of the anttbody [Boobis, A. R. and Sesardtc, T., personal commumcation] Plant P45Os thus appear much more heterologous than animal P45Os where antigenic homologtes [213, 2141 have aided the identtficatton of many P45Os and are reflected m the sequences of the P450 gene superfamily where cDNA and/or ammo acid sequences of over 60 gene products are now known [215]. Subsequent hydroxylation of p-coumaric actd to caffeic acid has often been thought to be catalysed by a phenolase of low specificity. However phenolase isoforms have been tmphcated as specifically catalysmg this acttvtty [216-2191. Alternatively, other mixed function oxtdases have been tmphcated and recently an FMN-dependent microsomal activity has been described from potato [220] The coumarate 3-hydroxylase has therefore not yet been identified [221]. The S-adenosylmethlonedependent caffetc acid 0-methyltransferase (COMT E C 2 1 l.-), m contrast, has been isolated from a number of tissues [222] and can be distinguished from those mvolved m methylatton of flavonotds [223, 2241. Further hydroxylatton to 5’-hydroxyferulic acid by a cytochrome P450 [207] precedes methylation to sinapic acid [224] At least two types of 4-coumarate: CoA hgases (4CL EC. 6 2.1 12 ) with differing substrate spectfictttes have been described [226229] Thus, type I mttially purified from soybean has highest affinities for 4-coumarate, ferulate and smapate, the CoA esters of which are substrates for the lignm pathway; a second tsoenzyme, type II, also purified from parsley cells as well as soybean has highest affinities for 4-coumarate and caffeate, the CoA esters of which appear to be the sole substrates for the first enzyme of the flavonotd/isoflavonotd pathway of species dependent subunit M, 4200&46000 chalcone synthase (CHS) [230-2341 Subsequent methylattons of the flavonotd B-ring appears to take place after the formation of the rmg structure by condensation with malonyl CoA [222, 2231. The CHS, of relevance to this review both as a control point of the relative flux through the pathway and m responses to pathogenests, also appears to have tsoforms [235-2371 that are the product of a multiple gene family that have now been identified and sequenced [238-2421. Similarly cDNA has been obtained for the M, 60000 parsley 4CL and has lead to the identification and sequencing of the two genes encoding this particular isoenzyme [202, 243, 2441. The synthesis of all these enzymes appears to be subJect to induction and repression by a large number of factors and 1s discussed below. In addition, the flux through the pathway appears to be under stringent fine

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G P BOLWELL

control parttcularly at the level of PAL where differenttal appearance of isoforms [200] has now been observed m parsley [245] A number of studtes have provtded evidence which suggests that mtra-cellular levels of transcmnamic acid or some metabolite of it may act as a signal for the regulation of the flux through PAL The effects of exogenous additions of cmnamic acid, which supresses PAL extractable activity IYI VW [246-2491 and L-Xammooxy-p-phenylpropiomc acid (AOPP) which acts as a powerful competitive mhibttor of PAL resultmg m the supermduction of PAL activtty [250-2531 as measured in oltro, can be interpreted m terms of the mvolvement of cmnamtc acid m a dual control mechanism mvolving inhibition of the rate of PAL synthesis and stimulation of the rate of PAL removal [2.%257] A more recent study usmg antibody and cDNA probes has demonstrated that cmnamic acid added exogenously to induced bean cells does not affect the rate of turnover of PAL subunits in VIUO,but rather mediates irreversible mactivatton of the enzyme [257, 2581 A non-dialysable factor from cmnamate-treated bean cells stimulates removal of PAL activity from enzyme extracts UI cure, this effect bemg dependent upon the presence of cmnamic acid and is accompamed by an apparent loss or reduction of the dehydroalanme restdue at the PAL active site (as detected by titration of the active sate by trtttatton or wrth affinity probes) m the absence of an accompanymg loss m the levels of immunodetectable enzyme subunits Such a mechanism accompamed by product mhrbitton of PAL catalytic activity by cmnamic acid especially m view of the apparent kmetic properties of the enzyme would be consistent wtth PAL acting as a self regulating valve controllmg the entry of phenylalanme mto secondary pathways from which fixed carbon may not be readily retrievable truns-Cmnamic acid may also have a feedforward effect on the operation of the flavonotd pathway since it activates chalcone isomerase (CHI E C 5 5 1.6) the second enzyme of the branch pathway [259] Exogenously added cmnamic acid is readily fed through the phenylpropanotd pathway. however, leading to increased accumulation of mtermediates and wall phenohcs so may not modulate these later enzymes [255, 257, 2601 It does however also have profound affects m swttchmg off the synthesis of PAL and the enzymes CHS and CHI sttuated at the start of the flavonoid branch pathway [258, 2611 All these effects are probably dependent on the state of the cells and it remains to be proven whether they truly represent mechanisms mvolved m down-regulation of phenobc metabohsm in wuo These studies wtll probably require the production of regulatory mutants either produced by selection, as has already been achieved [261a], or DNA technology In relation to the accumulation of wall bound phenohcs the 4CL enzyme also represents a tine control point, for apart from considerable differences m specificity the acttvity of both hgases ts modulated by the relative levels of AMP and ATP [ 1931 Study of such control mechanisms as a model system has important consequences for the operatton of secondary pathways when biotechnologtcal apphcations are desired [261, 2621 Enzymes ofl~gmnformat~on The two enzymes responsible for the reduction of CoA esters to the correspondmg alcohols, cmnamoyl-CoA NADPH oxtdoreductase (E.C 1 2 1 44.) and a cmnamoyl alcohol NADP oxidoreductase (CAD E.C.1 1 1 -) [263-2671 show substrate preferences for 4-coumaroyl-, feruloyl- and smapoyl-CoAs A

cDNA has recently been obtained encoding the M, 40000 CAD from bean [268] using the heterologous anti (poplar CAD) antibody which has allowed mvestigation of the mductton kmettcs of a enzyme specific to the hgnm pathway for the first time The CoA reductase has also been purified and has a subunit M, of 38 000 from poplar [266] A cDNA coding for the CoA reductase has rccently been obtained (Grand, C. personal commumcation). Polymerzsat~on Many types of crosslmkages both covalent and noncovalent occur m the wall, of which hydrogen bonding, dependent on the water content, must be the mam cohesive force, especially between the polysaccharides. In the primary wall other non-covalent bonds, ionic-bonds and Ca” bridges, may also contribute substantially [9] Covalent cross-lmkages such as dtferulolyl Imkages, isodttyrosme lmkages. whtch are found m primary and secondary walls. and m hgmn of secondary walls, profoundly effect the extensibihty, dtgesttbthty and adherence of cell walls [9] Followmg hgmficatton the water present m the growing wall is excluded and the matrix m which the cellulose nucrohbrils are embedded becomes hydrophobic producmg a compostte which 1s rigid [269]. Most of these crosslinkages are thought to be synthesized extracellulnrly under the action of peroxtdase and controlled by the availability of phenyl-linked wall polymers which may be preformed to some extent within the endomembrane system [270] and the supply of hydrogen peroxide Although the acttvity of peroxidase m the wall is dependent on specific isoenzymes and may vary tt does not however appear to ever be rate hmitmg There is also some evidence that the avatlabihty of ascorbate, possibly dependent on wall-bound ascorbate oxidase, may also be a regulatory factor consistent with its familrar role m the chloroplast [271] Thus polymertzation of hgnm wtthm the wall takes place after oxidation of the hydroxycmnamyl alcohols to mesomertc phenoxy-radicals The halflife of these free radicals 1s very short before they react together to give hgnm and to form linkages between hgnm and the polysaccharides of the wall [9, 27222741 Some of these features can be demonstrated In Lltro In contrast to the highly heterogeneous mixture of C--C and CO bonds generated m hgnrn formation, other phenohc linkages found m primary and secondary walls appear to be more specific The isodttyrosme ether- and dtferulate brphenyl- linkages, identified by controlled digestion of walls [9,275,276] occur within and between specific macromolecules, Isodityrosme linkages have been identified mtramolecularly m pepttdes whose sequence is homologous to extensm [122, 129, 130, 132, 2771 Smce soluble HRGPs are rapidly msolubihsed m the wall tt is thought that similar linkages may be generated mtermolecularly m two [278]. However these have not yet been Identified. Attempts to generate such hnkages tn uitro with salt extracted HRGP precursor and peroxtdase lead to polymerisation of extensm precursors to dtmers at least and msolubtltzatton 1130, 133. 279-2811 but most of the lmkages appear to be due to dttyrosme formation Dtferulate lmkages appear to be mainly found between pectic fragments [9, 2751 Esteriticatton of pectic arabmose residues by feruloyl-CoA appears to take place mtracellularly [133, 2823 and are subsequently polymertsed m the wall Although these types of crosshnkages, which for diferulate occur about once m every 100 sugar residues, are found wrthm the

Synthesis of cell wall components. aspects of control growing primary wall the mam cohesive force must still be the hydrogen bonding allowing a flexlbihty to the structure of the wall which depends on its most variable feature, the water content. In addition to lignin other hydrophobic encrustations are found. &berm is a complex polymer of long chain fatty acids into which cmnamlc acids such as ferulic and p-coumanc acids are mcorporated by covalent linkages. The phenylpropanolds of suberin are less methoxylated and more highly condensed than m lignin Polymerlsatlon of these aromatic components appears to be catalysed by a wall bound anionic isoperoxidase [154, 283, 2841. The ahphatic component contams substantial proportions of dlcarboxyhc acids but very little mldcham oxygenated monomers [285,286] This differs from cutin which originates as C,, and C,, o-hydroxy fatty acids which are modified to 9,10,16, or 18 hydroxy- or epoxyderivatives. The ahphatic precursors of both polymers are generated by analogous reactions [285, 2861. The reactlons specific to the hydroxylation of cutin include those catalysed by cytochrome P45Os for the lo-hydroxylation, 9,10 epoxlde formation and the w-hydroxylatlon [287-2891. Formatlon of the dlcarboxyhc acids of suberm are catalysed by a specific dehydrogenase [290] Mmerahzatlon such as slhclficatlon is also found, particularly amongst the grasses [291]. Although, deposition of sihcic acid or of a tropolone complex [292] 1s beheved to be non-enzymatic, it appears at the onset of secondary wall formation [293] or m response to mfectlon [294] and 1s therefore under developmental controls. Imtlal mvestlgations into these controls have been carried out durmg the development of grass hairs [295] and infectlon of bean [296]. Supramolecular

aspects

It ~111 be seen that the characteristic wall structure 1s dependent to a large extent on the type of matrix m which the cellulose mlcrofibrils are embedded. In contrast to cellulose, which is synthesized extracellularly [297, 2981, the matrix precursor are synthesized, transported and dlrected mtracellularly [299-3011 to be assembled extracellularly. Therefore sites of synthesis and mechanisms of transport constitute essential control points. Precursors and matrix polymers are synthesized within the endomembrane system, the endoplasmlc reticulum and Golgi apparatus and transported to the wall. In general, the capacity of plant cells for synthesis and secretion of extracellular components is more rapid than is often appreciated having a fli2 for transit of between four and ten mm [128, 300, 3021 Indeed, recent structural studies suggest that the P face of the plasmalemma can be in an extreme state of dynamic flux with what are probably both exocytosmg vesicles, as products of endomembrane, and apparently endocytosmg vesicles, as products of the plasmalemma, pIamIy discernible [303-305, Hawes, C. R., personal commumcation]. It IS only recently that the heterogeneity of such vesicles 1s beginning to be understood with, for example, the uneqmvocable demonstration of chathrm coated vesicles characterlstlc of endocytosls m plant cells [306-3093. The capacity for endocytosls has been consistently unrecogmsed m plant cells and the discovery of endocytotic vesicles may have important consequences for understanding cell slgnalhng as well as optlmlsation of the uptake of desired macromolecules introduced artificlally [305-3111. Similarly, the number of exocytosmg

1241

vesicles at any one time will have Importance for the rapidity of cellular responses to stimuli so that the composltion and amount of wall material deposlted may be dependent on the capacity for vesicle fusion. Also the dlrected deposition of such vesicles, as demonstrated by a number of electronmlcroscopic and inhibition studies, 1s apparently dependent on the operation of the cytoskeleton, especially the mlcrotubles, as IS the alignment of the cellulose mlcrofibrlls [3 12-3 IS]. It has often been assumed that the sites of glycosylatlon and the operation of the endomembrane system 1s similar to that extensively studied m animal systems [146, 319, 320, 3211 although some aspects of transport and secretion have been challenged [322] Many aspects of slmdar processes m plant cells are still to be resolved [321] but It 1s assumed that deployment of newer techmques such as lmmunogold locahzatlon ~111answer many questions Thus, the localization of synthetic enzymes, the site of synthesis and compartmentatlon wlthm the endoplasmic reticulum and Individual Golgl clsternae and the nature of the different types of transport vesicles may be better understood soon Most membrane-bound and probably all secreted proteins are probably synthestsed on membrane-bound rlbosomes and subjected to the constramts of molecular recogmtlon as to their subsequent fate and destmation. Some of the vast problems m understanding these processes may become clearer as the sequences of more of these types of plant protems become known In this way, some of the leader sequences are now recogmsed for secreted plant protems of known and unknown function [121, 122, 135, 179, 323-3251 Knowledge of such sequences may have Important consequences for genetlc engineermg where gene products Introduced mto transgemc plants are required to be dlrected mto the apoplast; for example chltmase or toxins [326] Recogmtlon and secretary mechamsms are generally presumed to be slrnllar to secreted products m animal cells but at the moment httle information IS available on the processmg of wall proteins unhke those transported mto protem bodies and other sites [9&104, 3271 These latter glycoprotems are also the best studled examples of the sites of locahzatlon of specific glycosylations Rather less sophisticated studies have mvestlgated the sites of glycosylatlon of both wall-bound glycoprotems and polysaccharldes by the apparent locahzatlon of enzymes actlvlties assayed in isolated membrane fractions tn uttro and m membrane fractions radloactlvely labelled tn owo Thus although activity can be detected for polysaccharlde syntheses in both endoplasmlc reticulum and Golgl apparatus, the bulk of the actlvlty 1s confined to the Golgl rn vwo [58, 3281. Other slmllar studies on enzyme actlvlties involved in glycosylatlon of wall proteins in isolated membrane fractions have localized a number of actlvltles [139, 329,3303. However, It IS antlclpated that use of antibodies specific for particular glycosylated epitopes for lmmunocytochemistry will resolve many of these questions unequlvocably smce endomembrane structures are defined by their appearance m the electron mlcroscope Development of such probes ~111 mcldentally aid specific ldentlfication of 1soIated membrane fractions when they have lost much of their characteristic morphology. The site of synthesis of hgnin precursors has long been controversial since the idea of a membrane bound multlenzyme complex was first suggested [331]. Part of the

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G P BOLWELI

problem resides m the fact that although the oxygenases are mlcrosomal, the first enzyme of the pathway PAL IS usually isolated as a soluble enzyme [191-1997 However PAL may be associated with the endoplastmc reticulum 1332, 3331 and at least 10% of lmmunopreclpltated PAL subumts are of mlcrosomai origin in bean (solwelT, G P, unpublished results) PAL has multlple forms, some of which may be compartmentalized [332-3341 for function m different pathways The synthesrs of hgnm precursors can be associated with Isolated mlcrosomal vesicles [335] which may be derived from those actively mvolved m transport to the wall by subsequent fusion with the plasmalemma m the intact cell Polymerlsatlon of hgnm subsequently occurs m the wall Vacuolar phenohcs may also be transported from the E.R 13361 Furthermore the endomembrane may be the site of synthesis and the cell wall site of deposltlon of non-glycosylated methylated Ravonolds [337]. One enzymatic actlvlty defimteiy associated with the plasmalemma appears to be the synthesis of cellulose [338,339] In this context, the underlying reasons for the difficulties experienced m the isolation of plant plasmalemma, which cannot be achieved m anything like the purity of animal cell plasmalemma [340], resides, m the author’s opnuon, m the rapid state of dynamic flux of plant plasmalemma described above. Besides brmgmg about dlfficultles m investigating the synthesis of cellulose this property also poses problems m the mvestlgatmn of putative cell surface receptors mvolved m varlous recogmtlon phenomena Cellulose mlcrofibrlls appear to be spun out from the plasmalemma into the matrix, the intimate mvolvement of the membrane being graphically illustrated by the profound effect of perturbatlons such as plasmolysls which lead to a switch over to callose synthesis [42] Through the observed changing orlentatlon of the mlcrofibrlls synthesis 1s thought to be directed by a mnvmg enzyme complex, which may be represented by the characteristic arrays of particles observed m freeze-fractured plasmalemma and which itself may be directed m some way by the orlentatlon of the mlcrotubules This process has conslderable importance since it has been estimated that it 1s the Inner 10% layer of the cell wall that 1s most important for the physical properties of the cell wall [341, Fry, S C, personal commumcatlon] With the capacity for rapid vesicle transfer this layer immediately overlying the plasmalemma has increased significance both for the exocytosmg wall modifying components and for a possible internalization of putative signal molecules Thus, vesicle fusion remains an important cellular event. It was studies on wall regeneration m protoplasts and m plasmolysed cells together with observations of the early fusion events m cell plate formatIon that has shown that matrix polymers are deposlted m the wall as a result of vesicle fusion. As with animal systems [342] the processes involved require both Ca’- and specific proteins m mttlai bmd~mg and subsequent fusion [321, 343-345) As yet there have been few direct studies m plant cells on the stages involved although putative fuslgemc epltopes have been ldentlfied The mvolvement of Ca* + 1s another example of the ublqultous importance of this ion [346]. Recently there has been intense interest m Ca’- moblhzatlon during cell slgnalhng part of which may be involved m the medlatlon of fuslgemc events Other processes related to Ca* + mobllizatlon may mvolve other components of cell slgnallmg such as the

mosltol phosphate pathways and protein kmases, though studies of such signal transuctlon pathways, so elegantly worked out m animal systems, are still very much m their infancy m plants It remains to be demonstrated If plants do indeed adopt similar mechamsms but as yet there 1s httle convmcmg evidence that all these pathways lead to gene actlvatlon m plant cells It may be that the plant cell wall may hold the key to many aspects of signal transduction which would be umque to plant cell> Control.5

Both endogenous and external stimuli can modulate profoundly ceil wall structure These include such stirnull as endogenous or externally apphed plant growth regulators, mechanical stresses, electromagnetic radiation, gravity, pathogenesls and the karlous biotic and ablotlc elicitor molecules some of which are probably mvolved m recogmtlon processes Many of these stirnull have target sites m common and may mvolve common pathways of information transduction so it IS useful to draw comparlsons of then effects at the molecular level However It IS important to note that where gene polymorphisms exist each mdlvldual gene may be placed m a dtfferent regulatory ctrcult so that although the same modified functional entity IS produced tt may represent a dlfferentlally synthesised lsoform A picture IS emerging of a relative If not umdentlcal basis to many of the changes observed m response to differing stlmuh that I$ now begmnmg to be ratlonahzed With a few notable euceptlont, the underlying basis to most of these changes rerldeb rn processes of gene activation de no1 o The recogmtlon of gene expression as the basis to these types of responses m plant cells has come from the deployment of 2D gel analysis and recombinant DNA techniques to Identify newly synthesized mRNAs coding for both known and as yet umdenttfied gene products Growth und p/am growth rtyuiator uctron The relatlonshlp of auxm action to the mductlon of growth and rts accompanymg changes tn the prkmary cell wall has long been a subject of Intense study and led for example to the ‘acid growth’ theory, and its subsequent mod& cation [325. 3471 A vclde range of earher studies mcludmg measurement of changes m the total RNA population and mhlbltor studies indicated that cell elongation may be medlated by auxm-regulated gene expresslon [325] Studies deploymg the newer technologies [325, 349.-3531 have shown that a number of RNA species accumulate, some after only 5-30 mm, after auxin apphcatlon to a variety of tissues A number of these genes have now been sequenced but as yet no function has been ascrlbed However, two auxm regulated genes from soybean, which appear to be related. contain repeated PPVYK sequences [325] which whilst dlffermg from extensm are slmllar to a related transcript ldentlfied earlier [120] It has therefore been speculated whether these proteins are destmed for the cell wail as post translatlonally modified HRGPs. which are functional during later cell dlfferentlatlon and maturation Although premature, it ma) well be that alterations m the expression of genes encodmg cell wall proteins by auxm IS important m these transltlons A number of enzyme actlvltles related to cell wall modlficatlon have been shown to be modulated by auxm action In man) different tissues the composltlon of the

Synthesis of cell wall components pectin changes during development and this can be modified, parttcularly the synthesis of arabinan, by the application of auxms [353-3573. But it 1s m the hemtcellulose composttion of the primary cell wall that profound and perhaps most stgmficant changes as regards aspects of control take place Thus during auxm-induced cell elongation m pea Increased xyloglucan and b (1+4) glucan synthase activtties occur while endo/l (1+4)glucanase acttvtty mcreases m the wall [61, 62, 3581 It is not yet known whether the basis of the changes m activity reflect protein synthesis de nova The major target site for the glucanase activtty 1s thought to be the xyloglucan and thus promotes wall loosenmg leading to growth under turgor and also to the productton of xyloglucan nonasaccharide As far as the regulatory action of ohgosacchartdes IS concerned, the case for the nonasacchartde acting as antiauxm 1s extremely strong [182-1851 so that a self-regulating system of auxminduced cell elongation being counteracted by the subsequent productton of the anttauxm from the cell wall may be constttuted [ 1811. There is little mformatton of the effects of gtbberellins on mdtvtdual wall components [359, Graebe, J., personal communication] although they too promote cell expansion expressed m terms of wall extensibility [360, 3611. However, gtbberelhc acid supressed peroxidase secretion and may atd cell expansion through prevention of crosslmkages m the wall [9, 180,362]. Gtbberellic acid-treated cells may also secrete pectins [ 1801 so tt will be mteresting to determine whether target molecules differ substantially from those m auxin-treated cells undergoing cell expansion. As yet there is little understanding of the signal transduction processes mvolved m the action of these growth regulators although putative receptors have been tdentified and localized At the moment, the evtdence for these 1s largely ctrcumstanttal It 1s a major challenge to eluctdate the intervening processes leading to gene acttvatton some of which, such as the proven targets for auxm action, are involved m wall modification. Development of Agrobactermm vectors leading to constituttve production of auxm or cytokmin with the subsequent acttvatton in transgemcs offer an excttmg approach to tdentifymg these genes [Schilperoort, R and Grand, C, personal communications] DEfSerentrat~on Stmtlar constderations of the nature of the control mechanisms apply to the changes m response to dtffermg sttmuh which are described subsequently. Thus, understanding the molecular events involved m plant cell dtfferentiatton IS a maJor goal of modern btology Changes m the components of the cell wall are a feature of this differenttatton. During the transition from primary to secondary wall synthesis there is a marked shift m the synthesis of the differing species of polysacchartde broadly characterized by the cessatton of pectm depositton and the enhanced deposttion of hemicellulose and cc-cellulose together with the onset of hgnification [269] The type of pectin, hemtcellulose and lignm monomers accumulated is species-specific and wtthm a species, of course, the range of cell types, often classified on the basis of wall morphology, 1s considerable [69]. Many differentiated cell types will contam charactertsttc combmations of these species-specrfic wall polymers Faced with this immense complexity of cell types the most accessible dtfferenttatmg ttssue system 1s probably that associated wtth vascular dtfferenttatlon and most

aspects of control

1243

notably the process of xylogenests which has been the SubJect of previous monographs [363, 3641. Some of these studies have documented the changes m enzyme activities associated with the synthesis of wall components in dtfferenttatmg cambial ttssues. In sycamore, tt has been shown that as the cells dtfferenttate there are large increases m levels of PAL and xylan synthase acttvtttes accompanied by losses m polygalacturonan synthase activity [57, SO] While in Pznus sylvestrrs, where the maJor hemicellulose is a glucomannan, large mcreases associated with cambial dtfferenttation are observed for the glucomannan synthase system [78]. It is thought that these increases are brought about by enhanced gene expression m response to growth regulator action Stmilar studies on dtfferenttatmg tissues such as hypocotyls have shown increases m acttvttles of enzymes mvolved in hemlcellulose synthesis accumulated during stages of dtfferenttation of vascular tissue along the growth axis [60, 61, 701. Valuable insights into the mteractton of plant growth regulators resulting m the characteristic changes m wall composltton, especially with regard to hgmfication, have come from studies of dtfferenttatton m tissue-cultured cells often as part of studies of morphogenesis in general. Reproductbly high levels of cytodtfferentiatton have been achieved for a variety of systems such as isolated cells, especially from Zinma, [365-3691, explants [37G373], callus cultures of both dtcotyledons and monocotyledons [374-3761, and suspenston cultured cells [377-3801 Ttssue cultures have proven good model systems especially tf induced changes still occur with the same ttmmg and magnitude as m developing intact tissues then there 1s no compelling reason to suppose that the basic controls differ between the two systems. Although the combination of plant growth regulators used for the mductton of dtfferenttatton is arrived at emptrtcally, as a general rule tt 1s brought about by a depletion of auxm m the medium which is often supplemented with a relative increase m exogeneous cytokmin and the provtsion of a carbohydrate source usually sucrose The auxm most commonly used to induce meristemattc, acttvtty is 2,4-D which is more slowly metabolized than IAA or NAA and is therefore more active in mamtammg the undifferenttated state. A number of studies have demonstrated loss of polypepttde species as analysed on 2-D gels and these may be associated with regeneration potential. In any case, depletion of endogenous 2,4-D on transfer to a 2,4D-free medium 1s probably an absolute prerequtstte for morphogenests which is inhibited by retention of this growth regulator The action of cytokmm is also modrfied in long-term cultures which may become habituated [381] leading to a loss of morphogenic potential [382] A deeper understanding of these phenomena IS of great importance m elucidating the control of gene expression during differentiation. Molecular studies have concentrated on the synthesis of spectfic RNA and protein species associated with differentiation. At present a number of spectfic proteins that are dependent on growth regulator treatment may be resolved by two-dtmenslonal PAGE [347, 348, 3831 Such studies illustrate the subtlety of the differentiation process since no extreme shifts m patterns of synthesis tend to be observed unlike for instance during pathogenesis (see below). The study of selective gene expression is probably best served by looking at specific markers. Many of these markers for dtfferenttatton remam func-

1244

G P BOLWELL

tionally umdenttfied and there have been few developments of probes (antlbodtes and cDNAs) wtth respect to differentially regulated proteins of known functton In contrast, the charactertsttc changes m enzyme activities associated wtth growth and vascular differenttation m tissue cultures have been documented. Thus increases m enzyme activities associated with pectm synthesis are observed during the periods of growth and cell division during the cell cycle C3.54, 3791 In nonditferentiatmg cultures the characteristic changes observed m relation to the cell cycle have been accurately mapped m a synchronous culture. Here most of the accumulation of glucan polymers occurs during Cl preceded by the necessary metabohc activity [54, 118, 135. 384, 3851 Transfer to morphogemc media induces xylan synthase activity associated with secondary wall formation during xylogenesis [375, 3791 Although results of prehmmary experiments suggests these changes may be due to de rtoro synthesis and possibly reflect gene expression this has not yet been demonstrated rigorously Unlike matrix polymers no mformation is yet available on the control of cellulose synthesis during differentiation In contrast to polysaccharide synthesis, more is knoan about the mduction of hgmfication where Increases m the mdtvtdual activities of the pathway from shikimtc acid to hgnm and specific isoenzymes of peroxidase have been documented to varying degrees m many different systems Although perhaps not as rigorously demonstrated as m the responses to other stimuli, increases m activities of PAL and isoenzymes of 4-coumarate hgase during differentiation probably reflect increased gene expression [374, 315, 37773801 These aspects of differential gene expression are crucial to the development and maintenance of specific cell types The transcriptional control mechanisms mvolved m estabhshmg these developmental states still remam elusive as regards the interplay of plant growth regulator action that promotes them One way m which the cell wall might be mtimately mvolved m control of morphogenesis might be rn the provision of ohgosaccharms that regulate morphogenesis Thus, an ohgogalacturomde isolated from primary walls of suspension cultured sycamore cells can brmg about modulation of apparent auxm and cytokmin action during tobacco callus morphogenesis [186] These fragments like the xyloglucan nonasaccharide may hold the key to many aspects of planf cell signallrng if they could be demonstrated in two Stress and ethylene Environmental factors such as light, temperature, water relations or mechamcal constraints can also have considerable influence on wall components The effect of light on ettolated seedhngs IS an obvious example but the changes m the wall components that ensue are, of course, part of the genera1 developmental programme of growth and differentiation triggered durmg photomorphogenesis, a subJect too complex to be treated here The mduction of the phenylpropanotd pathway by hght is of course very well documented and under light stress conditions (high or low intensity white hght or UV light) the products tend to be channelled mto the formation of protective flavonotd compounds [ 1931 Similarly, although many of the effects of temperature shock are begmnmg to be elucidated at the molecular level [386], none has yet been shown to be related to the synthesis of wall components Although water deficits have profound effects of cell wall synthesis and cell enlargements and also on the levels of hgnm precursors and other secondary compounds no clear relationships

have been established and most studies relating to the wall have been physiological [387] Also, for osmotic stress extensive mvestigations have been directed to parameters such as resptratton, accumulation of low M, compounds and lipid metabohsm and other than treatments leading to plasmolysis, few studies have determmed the direct effects of mcipient water stress on wdll metabohsm Under extreme conditions of plasmolysis mcorporation of sugars other than arabmose mto newly synthesised polysaccharides is decreased 13881 A protein which by virtue of its hydroxyprolme content may be related to wall-bound proteins accumulates m salt stressed cells [I271 In contrast. the effect of mechamcal constraints as regards the synthesis of cell wall components have been well characterized at the biochemical level Thus a constant mechanrcal perturbation SIIITIUlates the directed deposition of callose. the thigmotropic response [389] Cdllose synthesis IS also a feature of wounding [41] and since woundmg has many features m common with pathogenesis, which also present\ additional aspects of control, both are discussed m more detail below The whole subJect of the effects of uoundmg on plant cells has received some attention and much (Jf the biochemistry of the responses is now well understood [390--3921 Ho&ever. here too it IS the mechamms of signal transduction that lead to increased gene expression remam elusive, other than to belteve they may be related to depolarization phenomena exhibited by damaged cells [393-3961 In contrast, signal transduction at the molecular level m response to woundmg monolayers of ammal cells is begmnmg to bc understood [397. 398, Jones, D , personal commumcation] Besides the stimulation of callose synthesis. Lcoundmg also effects the synthesis of other wall components and these are classically associated with the production of ethylene [399402] A large number of metabolic dctivities are stimulated m response to woundmg these mclude the general gross responses of regeneration of membranes, enhanced respiration, protein synthesis, stimulation of secondary pathways and changes m growth regulator activity and m some cases cell division [390--3921 Cell walls are regenerated at the wound site with enhanced depositton of hgnm- or suberm- like mdtenals and HRGPs The underlymg basis of these changes, with the exception of the synthesis of wound callose. appears to reside in Je noro gene expression However, once agam it 1s important to emphasise that differential gene expression mediated by different regulatory circuit\ in response to each sttmulus where gene polymorphisms occur may well be operating Thus stimulation of the transcnption of PAL. for example. by wounding or ehcitor action may mvolve differential expression of the different genes espectally m relation to the timmg of the responses Although a direct role for ethylene rn disease resistance IS controversial there is abundant evidence for n role m the transmission of the wounding response Ethylene stimulates general mRNA and protein synthesis and modulates the level of specific transcripts 1403. 4041 Thus similar transcripts of \pecilic HRGPs can be induced by woundmg and ethylene, translated and processed, although subtle differences m the range produced may be observed [120 122, 4051 Ethylene also brings about a cessation m xyloglucan deposition through loss in B-glucan synthase and xyloglucan synthase activities though unlike auxm treatments no enhanced endo /j [1+4]glucanase activity is observed [61. 621 Other hydrolases are synthesized howo\er Thus the differential

Synthesis of cell wall components: aspects of control synthesis of specific hydrolases occurs either in wounding or under conditions of terminal differentiation such as abscission or fruit ripening. Ethylene generally stimulates transcription of chitinase probably as a defense response which interestingly may also be observed at abscission zones [17&173, 4061. Enhanced transcription of polygalacturonase genes is particularly well documented m ripening tissues [164, 1793 and /I Cl-33 glucanases show enhancement by ethylene action [166, 4073. This may involve transcription of specific isoforms of a variety of hydrolases at abscission zones [cf. 4081. Although ethylene stimulates the accumulation of many specific mRNAs there is as yet no clear picture of the mechanisms involved, the putative receptor and the subsequent signal transduction mechanism The mechanism of response coupling of the mmal stimulus to ethylene production also remains elusive but is crucial for understandmg such processes of commercial importances as ripening, senescence of flowers and leaves and abscission. Pathogenesis and elicitor actron. Although the involvement of the plant cell wall in adherence is a matter of conjecture [409], following binding of a pathogen to the plant cell surface, a series of characteristic changes m the host cell wall appear immediately underlying the infection site. A number of electron microscopic and cytochemical studies have revealed the similarity of these papilla-like and other structures below the site of spore or penetrating hyphae in many diverse families of dicotyledons and in monocotyledons, particularly the Gramineae [41&413] Similar encrustations of wall materials have been observed in vascular tissues where these are target sites for pathogens. These studies suggest a callosehke polysaccharide material IS usually deposited which becomes progressively encrusted with hydrophic or lypophihc material which in general appears to be both glycoprotemaceous and lignin-like. In some species, especially those of the Solanaceae the complex lipidphenolic, suberin is deposited at the site [ZSS] These changes, although more locahzed, resemble those found as a general wounding response but other components, intimately hnked to disease resistance, must occur in addition to the recognition phenomenon. Understanding the highly localized wall reaction, probably linked to the hypersensitive response followmg the Initial recognition event, indicates that synthesis of wall components may be of fundamental importance to disease resistance. Although patently a component of plant disease resistance many of these characteristic wall changes would not be expected to represent direct products of resistance genes per se since these changes are represented in both resistant and susceptible interactions where the timing of their appearance differs. The deposition ofcallose is an early event in these interactions, The phenomenon is widespread, being observed not only in microbial attack but also, as described above, during mechanical stimulation, wounding or disruption of the plasmalemma-wall interface, which can also occur during normal cell development such as in sieve plate formation m phloem. Callose formation can in fact precede the characteristic ethylene production seen m some of these phenomena. While the evidence accumulating points to many responses involving changes in the patterns of the synthesis of wall components having an underlying basis in gene activation, with possibly some element of post-translational modification, deposition of callose appears to be an exception. Thus callose formation in suspension cultured cells of soybean, in response PHyTO276-B

1245

to membrane perturbations brought about by ehcitor action, is due to stimulation of /I(1+3)glucan synthase activity which possibly represents a modulated activity of the cellulose synthase system, and may be coupled to an influx of Caz+ ions across the plasmamembrane [41,119, 414, 4151. Wall-bound enzymes such as acid phosphatases can also be activated by CaZ+ ions [416] and secretion of peroxidases [417] or of pectic fragments by plasmolysed cells [418] are Ca2+ dependent so that Ca2+ fluxes may therefore play an essential part m establishment of changes in wall structure stimulated by pathogenesis. Whether such ion-fluxes can be coupled to some mechamsm leading to gene activation, perhaps as a second messenger, requires further exammation. In addition to these activation mechanisms the mfection of hypocotyls of cultivars of Phaseolus uulgarls with comdia of different races of Colletotrlchum lindemuthzanum, for example, causes marked coordmated increases in the rates of synthesis of PAL and other enzymes of phytoalexin production as measured by rn urtro translation and for PAL and HRGPs as measured by blot analysis [203, 237,419,420]. Incompatible responses are characterized by early accumulation of these mRNAs and a hypersensttive response; during compatible interactions there is no early response but rather a later accumulation of mRNAs associated with phytoalexin production during attempted lesion hmitation. These types of study mdicates that specific accumulation of defence related mRNAs is an early component during race-cultivar specific interactions and that signal transmission occurs to pre-activate defence genes m hitherto uninfected cells. Expression of these genes leads subsequently to the accumulation of HRGPs and ligmn-like phenols at the infection site. In many ways the modified nature of these materials compared to the related structures usually accumulated resembles the transition from net cellulose to callose synthesis occuring during the perturbation of the plasmamembrane. The modified nature of phenolic material might be explained perhaps by premature exposure of phenylpropanoid precursors to phenolases and peroxidases as a result of membrane disruption leading to free radical formation of species other than lignm alcohols. These might react with other polymers before deposition. It is apparent that during the hypersensitive reaction target cells experience highly disturbed metabolism leading to the production of numerous highly reactive free radicals including superoxide anion [421423] Similarly abnormal metabolites produced by wounded cells can also act as attractants for pathogens and inducers of virulence genes [409]. Use of tissue cultures of, for example, parsley, soybean or French bean treated with elicitor molecules, derived from pathogens, also exhibit many of these changes m wall components found m the intact mteraction, though accumulation of components would not be expected to show the localized deposition found m the intact mteraction. Mechanisms of gene activation have been indicated to varying degrees of technical sophistication for increases m activity of PAL [202, 203, 419, 4244291, probably cmnamate-4-hydroxylase, 4-coumarate ligase [202,428,429], cinnamyl alcohol dehydrogenase [268] in hgnin-like synthesis, and prolyl hydroxylase [143], probably arabinosyl transferase [ 1071, and various forms of prohne-rich precursors [128, 419, 420, 430, 4311 m HRGP synthesis. The hydrolyases. chitinase and p [ 1-+3]glucanase [326,426] are also induced but it is not yet known whether they are targeted mto the wall These

1246

G P BOLWELL

Increases occur albngstde species-specific Increased gene activatton mvolved m phytoalexm accumulation [419, 4244291, pathogenests related protems [432,433] some of which are now known to be tsoforms of chttmase @&ieeT, iJ.-, personaf commumcation j,and- m the Intact situatton, protease mhtbttors [434]and_ethyiene prod-uction [4.$44,435-J iJetailed_ studies of- the ttmmg of~such responses have been made to attempt to discover putattve causal lurks m order to understand the basis of dtsease resistance Although transcrtpt run-off experiments have estabhshed that gene acttvatron can occur withm 30 mm of addttion of ehcnor to suspenston cultured cells tt IS now generally considered that genes conferrmg true reststance encode products mvolved m intttai recognition events Attempts have been made to Isolate specific cell surface receptors that bmd ehcttor molecules and one such putative mteractton has been described [436] Ehcttor molecules may be hydrolyttc products of fungal or host cell wall [410.437,438] The vartety of ehcttor molecules IS ever mcreasmg and meludes examples of ohgosacchartdes, hpids and protems or glycoprotems However, it seems dtfficult to envtsage how, faced wtth such mherent variety, resistance and susceptibthty could arose from coevolved receptor-hgand mteractions as has been postulated With such a diverstty of sttmuh gtvmg rise to stmtlar changes m wall components whtch can be htghly locahzed, a perturbation of an endogenous self-recogmtton process m the form of continual Interplay between wall and protoplast could be an alternattve basts of some of these responses Certamly the actton of these molecules m brmgmg about rapid membrane depolartsatton events based upon multiple tonfluxes [439441] as seen m both the cell culture and m mfectton sites could be symptomatic of a general membrane response involvmg many parameters rather than due to a parttcular target receptor Such a perturbatton would be tmmediately fed back through the endomembrane system rapidly generatmg a number of novel compounds or leading to an abnormal accumulatton of matertal which could act as stgnals The response couplmg mechamsms leadmg to gene activatton remam obscure, however, but are currently an area under intensive mvesttgation These may be related to the types of signallmg mechamsms known to lead to gene acttvation m animal cells, such as m responses to growth factors or during the Ca’+ ton mflux stimulated acttvatton of Cfos oncogenes On the other hand, as yet umdenttfied modes of inter- and mtracellular commumcation may be mdtcated One study for example tmphcates dtrect nuclear targettmg of fungal-derived ehcttor [427] Such a mechamsm has become more feastble with the establishment of a rapid endocytotic pathway m plant cells Armed with probes to study early events m gene acttvation and with the acqutsion of sequences for crs-acting controllmg sequences functtonal analysts at the gene level becomes feastble, possibly leading to the identification of the putatrve tmns-acting factors Signal transductton mechamsms may then become less Intractable, but ~111 probably require absolute identtficatton of the ehcttor molecules actually actmg in uzuo. Some of these molecules are thought to be products of the host cell wall [409, 437, 4381 Thus although ohgogalacturomde fragments produced from Isolated walls were first identified as inducers of protease mhtbitors or phytoalexms they are also capable of ehcttmg changes m host wall components (Murphyi~II Jopersonal co-mmumcatmn) Although one

difficulty in explammg then actton m the piant has been noted [442] at the cellular level they are certamly effective m a number of systems. Then mode of action can be synergtsttc with other ehcitors [443] and a number of studtes point out ditferences, possibly temporal1 m ehcitor action in the ditirentiaf activatton ofrelated- genes The action of microbiaf hyd-rofases specific for pectm degradatton IS also thought to brmg about resistant responses through the production of pecttc fragments [444] Apphcation of these enzymes brmgs about rapid ton fluxes [445] The stmilarity of the range of responses m the type of product molecule Induced to all these many dtfferent primary sttmuh as regards syntheses of wall components ts of course strtkmg However, since the responses are not tdentical m timing and-site of-depositton tt must mean other controls must operate m some extremely subtle way and the very essence of non-self recogmtion still remains obscure

CONCLCSIONS

The whole area of plant cell wall metabohsm offers an excitmg challenge smce tt requires an understanding of molecular events at all levels of orgamsatton Thus, mcreases m our knowledge are unlikely to be brought about by apphcation of smgle technologies due to the complex modtfications and mteractions that contrtve to assemble and change the extracellular matrix Yet it IS now reahsed that these dynamic properttes are fundamental to the adaptabthty of the mdtvidual cell and to the exchange of mformatton wrth the envnonment, tn addition to the structural role played by the plant cell wall Thus these properties deserve to be explored, particularly as plant science moves mto a new age In the area of molecular btology, where the search for regulated gene products accelerates, tt IS becoming apparent that many of the earhest genes Induced m response to a wide variety of sttmuh are mvolved m the modtfication of existmg wall structures Although the mechamsms of signal transductton remam obscure, wall products can act as signal molecules Thus it 1s obvious that the cell wall IS mttmately mvolved as part of the ‘sensmg’ of the envnonment and m ‘respondmg’ through the ensumg changes It 1s striking how many of these changes. both during normal development and under conditions of stress, have many stmilarities However the subtle differences observed suggest addtttonal controls operate both at the molecular and supermolecular levels Identtficatton of the signal transductton pathways and mechamsms of gene swttchmg together with the post-translattonal aspects of protein functton, mcludmg the syntheses of polysacchartdes, remam the greatest challenges If some genes mvolved m cell wall synthesis Jam the ranks of those suttable for transformatton studies as a view to posstble genetic engmeermg, for example, of disease resistance, then all the aspects of subsequent processmg should be recogmsed

.4cknowledgements--I am Indebted commumcatlon, whose contrlbutlon VIOUS. Additional discussions with Durst and Dr J Ebel have been especially Profs J E Varnex_L C

to all those cited as personal through discussion IS ob-

Dr D P Delmer, Prof F most enlightening I thank Fowke.

Go .A Machchldn.

Synthesis

of cell wall compc ments

D G Rohmson,~ M T Esque& -Cwy& C .I Lamb and Dr C T. Brett for generously provldmg reprints and preprints. I dedicate thts review to Prof D. H Northcote who Introduced me to the whole field of plant cell wall metabolism

REFERENCES 1 Goldberg, R B (1986) PM Trans. R Sot Lend. B. 314, 343 2 Darvdl, A, McNeil, M. Albershelm, P (1980) m The Blochenustry of Plants Vol. I (Tolbert, N. E. ed), p 91. Academic Press, New York. 3. McNed, M , Darvdl, A G Aman, P, Franzen, L. -E and Albershetm, P. (1982) Meth Enzymol 83, 3 4 McNeil, M , Darvdl, A G , Fry, S. C and Albershelm, P (1984) Annu Rev Blochem. 53, 525 5 Darvdl, A G , Albershelm, P , McNeil, M , Lau, J M., York, W S, Stevenson, T T., Thomas J, Doares, S., Golhn, D J., Chelf, P and Davis, K (1985) J Cell SCI Suppl 2, 203 6 Selvendran, R R (1985) J Cell SCI Suppl 2, 51. 7 Selvendran, R R., Stevens, B J H and O’Nedl, M A (1985) The Blochenustry of Plant Cell Walls (Brett, C T. and Hdlman, J R., eds), p 39 Cambndge Umverstty Press, Cambndge 8 York, W S, Darvlll, A G, McNeil, M., Stevenson, T. T. and Albershelm, P (1985) Meth Enzymol. 118, 3. 9 Fry, S. C. (1986) Annu. Rev Plant Physrol. 31, 165 10. Vlan, B , Bnllouet, J. M. and Satlat-Jeunemaltre, B. (1983) B~ol. Cell 49, 179: 11 Ruel, K. and Joseleau, J P (1984) Hlstochenustry 81, 573. 12 Vian, B. (1986) m Biology and Molecular Biology of Plant-Pathogen Interacttons (Bailey J A., ed ) p. 44. NATO ASI Series, Plenum, New York I3 Roberts, K, Plulhps, J, Shaw, P, Grief, C and Smith, E. (1985) m Btochemistry of Plant Cell Walls (Brett, C J and Hdlman, J R , eds), p 126 Cambndge University Press, Cambridge. 14. Moore, P J., Darvill, A G , Albershelm, P and Staehelm, L A (1986) Plant Physlol. 82, 787 15 Moore, P. J and Staehelm, L A (1985) Plant Phystol Suppl 8441 16 Preston, R D (1974) The PhysIcal Biology ofthe Plant Cell Wall Chapman & Hall, London 17 Nevdle, A C , Gubb, D C and Crawford, R M (1976) Protoplasma 90, 307 18 Roland, J C , Vlan, B and Rels, D (1977) Protoplasma 91, 125 19 Vtan, B. and Roland, J. C (1986) Protoplasma 131, I85 2(1. Quatrium. R. s,. CZ&%l~~. 1, R.,. &l&X-WalrJIh;. V and_ Doubet, R S (1985) J Cell Scl. Suppl 2, 129 21 Quatrano, R. S., Gnffing, L R, Huber-Walchh, V and Doubet, R S (1986) m Cell Walls ‘86 (Vlan, B , Rels, D. and Goidberg, R, edi); p. 26 Universlte Pierre et M%rie Curie, Paris 22. r&m&. 11.. W ,_ Gi&h~t,. a,. M~sJlam,. R.. P and Heuser, J E. (1986) J Cell BIO~.103, 405. 23 Hayashl, T., Marsden, M P F. and Delmer, D. P (1987) Plant Physlol 83, 384 24. Lennarz, W (1983) Meth. Enzymol. 98,91 25 Schachter, H ,Naraslmhan, S, Gleeson, P and Vella, G (1983) Meth. Enzymol 98, 98 26 Kornfeld, R. and Kornfeld, S (1985) Annu. Rev Blochem. 54,631 27 Kragg, S. (1985) Curr TOPICSMembr. Transp. 24, 181.

aspects

of control

1247

28 mmer, D_ I?, Benuman,~ M,~ Klem,~ A. S Jo Raslq, A., Mitchell, B., Wemhouse, H., Alom, Y and Callaghan, T (1983) J. Appl. Polymer Sci. 37, 1 29. Camlrand, A., Toresslan, K , Hayashl, T and McLachlan, G. (1985) Can. J Botany 63,867 30. McLachlan, G. (1985) m BIochenustry of Plant Cell Walls (Brett, C T. and Hdlman, J. R, eds). p 199 Cambridge Umverslty Press, Cambridge. 31 Elbem, A. D. (1979) Annu. Rev. Plant Physol 30, 239 32 Lehle, L and Tanner, W (1983) Blochem Sot. Trans 11, 568 33 Chnspeels, M J (1985) Oxford Surveys ofPlant Molecular and Cell Biology 2, 43. 34. Callaghan, T. and Benuman, M (1984) Nature 311, 165 35. Durr, M., Badey, D S. and McLachlan, G. (1979) Eur J Blochem. 97,445. 36. Franz, G. and Heimger, H. (1981) m Encyclopaedla of Plant Physrol New Series Vol 13B, p 47. Springer, Berlin 37 Delmer, D P. (1983) Adv Carbohyd Chem Blochem 41, 105. 38 Delmer, D. P., Thelen, M. and Marsden, M. (1984) m Structure, Function and Blosynthesls of Plant Cell Walls (Dugger, W M and Bartmcki-Garcia. S., eds), p 133 Waverley Press, Baltimore. 39 Delmer, D P., Cooper, G, Alexander, D, Cooper, J, Hayashl, T , Nltsche, C. and Thelen, M (1985) J. Cell SCI Suppl. 2, 33. 40. Jacob, S R. and Northcote, D H. (1985) J Cell Set. Suppl 2, 1. 41 Kauss, H. (1985) J. Cell Scl Suppl 2, 89 42. Northcote, D. H. (1986) J Cell Scr Suppl. 4, I15 43 Meler, H., Bucks, L. Buchala, A. J and Homewood, T (1981) Nature 289, 821. 44. PilIonel, Ch and Meler, H. (1985) Planta 165, 76 45 Read, S. M., Thelen, M. P and Delmer, D P (1986) m Cell Walls ‘86 (Vlan, B., Rels, D. and Goldberg, R eds), p 308 Umverslte Pierre et Mane Curie, Pans 46 Thelen, M. P and Delmer, D. P (1986) Plant Phys101 81, 913 47. Wasserman, B and MacCarthy, L. (1986) Plant Physlol. 82, 396. 48. Delmer, D. P. and Read, S M (1986) m Cell Walls ‘86 (Vian, B , Rels, D. and Goldberg, R , eds), p 3 I2 Umverslte Pierre et Mane Curie, Paris 49 Read, S M. and Delmer, D P (1987) Plant Physlol. (m press) 50 Sloan, M E., Etberger, L L. and Wasserman, B P (1986) Plant Physlol Suppl 80, 159 51. Elberger, L. L. and Wasserman, B P (1987) Plant Physrol 83, 982 17- WWk~W!QJldt&W L,.kllb,.C h kUKLMLJLqD L (.Wq!. Blochem. &ophys Res. Comm 46, 245 53 Montague, M J and Ikuma, H (1978) Plant Physrol. 62, 391 54. Ammo, S, Y&hihisa, T. and- Komamme, A. (19g5) Plbnt Cell Physlol 65, 67

56. Odzuck, W. and Kauss, H. (1972) Phytochenustry 11,2489 57 Dalessandro, G. and Northcote, D H. (1981) Planta 151, 53. 58 Bolwell, G. P. and Northcote, D. H (1983) Blochem J. 210, 497 59 Villemez, C L. and Hmman, M B (1975) Plant Phys101 Suppl. 56, 15. 60. Ray, P M. (1980) Blochim. Btophys Acta 629,431

I248

G P B~LWELL

6.1.

G (1986) m Cellulose Struc62 Hayashl, T and MacLachlan, ture, Mod$tatlon and Hydrolysu (Young, R A and Rowe]], R M , eds), p 67 Wiley, New York 63 Hayashl. T. Kato. Y and Matsuda.. K (J980). P&t Cell Phrtrol 21. 1405 64 Hayd.shl,. T Kate,. Y and Mahsuda. Is_ (J_981). J Bmchem. 89, 325 65 Hayashl. T and Matsuda. K (1981) PIunr C’rll Physrol 22, 1571 T md Mamu&_ K- (.1_9Rl)..I &nl. Chem. Z%,. 66 k&XhJ.. 1117 61 Hayash!, T, Nakapma, T and Matsuda, K (1984) Ayrrc HI,,1 Chrm 411 1023 68 Campbell, R M , Wdldron, K W and Brett, C T (1986) m Cell W&F ‘86 (Vlan, B , Rels, D and Goldberg, R , eds), p 202 Ilmverxne Pierre et Mane Cuneq Pans 69 Waldron, K W and Brett, C T (1985) m Btochemtstry of Pkmt Ce!I Walls (Br~_tf,~C IY and_tillman, J R eds), p 79 CambrIdge Umverslty Press, Cambridge 70 Wnldron. K W and Br&, C T (!983) Bmchem d 2l3, 115 7l Elbem, .A D and~Hassld, W Z (!966) Brochem~ Bmphyr Res Comm 23, 311 12 Elbem, A D (1969) J B~ol. Chem 244, 1608 73 Hrller_~J S andVlJJeme;r. C L (1972) BrnL-~em 1 lL2&243 74. Heller, J S and Vlllemez, C L (1972) &o&em J 129, 645 75 Vlllemez, C L (1974) Arch Blochem Blophys 165, 407 16 Hmman, M B and Vdlemez, C L (1975) Plant Phy~ol 56, 608 77 Brett, C T (1981) J Exp Botany 32, 1067 G, Puo. G and Northcote, D H (1986) 78 Dalessandro, Planta 169, 564 79 Vdlemez, C L , Lm, T-Y, Hassld, W 2 (1965) Proc Nat/ Acud SC! U S A 54, 1626 G and Northcote, D H 80 Bolwell, G P, Dalessandro, (1985) Phytochemrstry 24, 699 81 Cummmg, C M and Brett, C T (1986) in Cell W&s ‘86 (Vnm. B Rels, D and Goldberg, R , eds), p 360 Umversfte Pierre et Marie Curie, Paris 82 Bolwell, G P and Northcote, D. H (1984) Planta 162, 139 83 Lang, W C (1982) Plant Phy.szo[ 69. 678 84 Hdyashl, T and MacLachlan G A (1984) Phytochemzstry 23. 487 85 Mellor, R B and Lord, .I M (1979) Pkzntu 147, 89 86 Coughlan, S C (1977) FEBS Letters 81, 33 87 Green, J R and Northcote, D H (1979) J Cell SCI. 40.235 8X Camirdnd, A and McLachlan, G A (1986) Plant Physrol 82, 379 89 Camuand, A, Brummell, D and MacLachlan, G A (1987) Plant Phyvol 84, 753 90 Lehle, L (1980) Eur J Blochem 109, 589 91 Sharma. C B, Lehle, L and Tanner, W (1981) Eur J Blochem 116, 101 92 Lehle, L (1981) FEES Letters 123, 63 93 Horl, H, Jane,. D W and Elbem, A D (1982) Arth Brochem Blophys 215, 12 94. Faye, L , Johnson, K D and Chnspeels, M J (1986) Plant Physrol 81, 206 95 Bol11n1, R. Vltale, A and ChrIspeels, M J (1983) J Cell Biol 96, 999 96 Vitale, A, Ceriotti, A, BoJhm, R and ChrIspeels, M J, (1984) Eur J Blochem 141, 97 97 Vltdle, A and ChrJspeeJs, M J (1984) J Cell Btol 99, 133 98 ChrIspeels, M J (1984) Phd Trans Roy Sor B304, 309

101

!Q2 I.03 Sz~urmlo, T ,. Kaushal.. G. P ,. HJ,n,. H. act_ FJbem.. A. D (1986) PIant Physrol 81, 383 104 Bolhm, R. Cerlottr. A. Dammdtx. M G and Vltale. A (1985) P/ant Phyvol 65 15 L. and. Chr.!speeJs,. M J. (.!.%h). tn. C& B!‘&lll.\. ‘46. !.05. Far! (Vlan, B, RCIS, D and Goldberg, R , eds). p 4X Universite Pierre et Marx Curie. Parn G 4 !!984) Bmchem I a-7. !06 Hdyash~, T and MacLachlan. 791 25. 1807 107 Bolwell, G P (1986) Phytochemrvq 1.08. !‘&rr,. 4. L (.!9.72) P!nnl. 4h~:Elol. SO,. 275 109 Owlens, R J and Northcote, 66! 110 Laughlin. L F, Northcote. 0 ,.I a. ,_L’ Ph;~frrchc?nr’~~-~ ‘6 i o1 111 Green. J R dnd Northcote, 66: D FL (!983) Ph/l !!2 Northcotc

114 115 116 117 118 119 t.xL 121 122

D I-1 11981) Bloc hem .I 196. D H dnd Roberts,

K (1987)

D H (1979) Bmcltrm Trtmc- &,I

Sot

.I 178.

I_rmd~t-W@

107 Dale*andro. C; and Nor:hcote , r) u (! 977)s?c!wn2 .! 162, 267 Loewus, F A and Dickmson. D B (1981) Em I’(lopaedm of Plant Phyvoloy~ New Serle5 13A, 193 Dalessandro, G dnd Northcotc D H (1977) Phi tochemlstrl 16, 853 Fry, S C and Northcote, D H (1983) Planr Phcstr)i 73. 1055 Capita, N C and Delmer, D P (1981) J B/o/ Chem 256, 308 Ammo, S, Takeuchl. Y Komammc, A (1985) Phmt Cc/l Phyrro/ 64, 11 I Kauss. H and Jebhck, W (1987) Plant Scr 48, 2 SheJI,. I .ulL \r,,. 1 F. (.l.w5). evw. ~V.121.1. 4r:luL b_!. C’ S A 82, 4399 Chen, J dnd Vainer, J E (1985) EMBO J 4. 2145 Showalter. A M and Varner J E (1987) m The Blo-

chcvmw v oj Plum\ Vol II (Marcus, A, cd), (m press) 123 Clarke, A E, Anderson. R L and Stone B A (1979) Ph~tochenurtq 18, 521 124 Fmcher, G B , Stone. B A and Clarke, A E (19X3) Annu Rer Planf Phywl 34. 17 125 Lord. J M (1985) ~Vrw Pltytd 101, 351 126 Casalongue. C and Pont Lezlcd R (1985) Plant Cell Phwol 26, 1533 127 Smgh, N K , Handa, A K, Hasegawd, P M and Bresr,m, R A (I 985) Plant Ph)sml 79. 126 128 Bolwell. G P (1987) f%mrtr 172. 184 129 Cooper. J B dnd Vdrner, J E (1983) Blochem Bwphbss Re\ Comm 112, I61 130 Cooper, J B and Varner, J E (1984) Pkmr PAVvoI 76.4 I4 131 Stuart. D A and Varner. J E (1980) P&t P~,I trol 66. 787 132 Smuh. J I Muldoon. E I? i W111,ud. J J nnd~Lampor!, D T A (1986) Ph~trxhemivtrv 25. 1021 133 Fry, S C (19861 in Ce[l Iz’alls ‘86 (Vnm, B , Rels. D and Goldberg, R , eds), p 12 Unrversne Pierre et Marlc Curie. Pdrls 134 Sduer. A and Robmson, D G (1985) Pkmta 164. 287 135 C’ondlt, G and Meagher, R (1986) Nature 323, 178 136 Vdmer, J E and Cdssab, G 1 (1986) Narure 323, 110

Synthesis 137 Tanaka, M , Shlbata, H. and Blophys Acta. 616, 188 138. Cohen, P B , Schlbecl, A and Phystol 72,754 139 Bolwell, G P, Robbms, M Btochem .I 229, 693 l-4(1 BlankmstpJn;. P i_lag,. W C Planta 169, 238

Uchlda,

of cell wall components

aspects

T (1980) &ochlm.

175 Khs, F. M., Dalhmzen, R and Sol, K (1974) Phytochemlstry 13, 55 Fincher, G B (1983) Plant 176 Masuda, H, Ozaki, Y., Ammo, S and Komamme, A. (1985) Plant Cell Phystol 26, 195 P and Dixon, R A. (1985) 177. Nagahashl, G and Slebles, T G (1986) Protoplasma 134, 102. and_ R&m.m,.D.. G (.I_%%_). I_% @NC’Jl,.R. k,.~!)Ilk,.~k ~.,.b&,.W: S,.&ind@. G and Albershelm, P (1986) PIant Physrol. Suppl SO, 31 13.9 G~_IP~w,. D ,_ !&urn-. M_ 1,. Slsliller,.~A.,.hy.,. I ,_Lrd,. C R.;. S&u& W ,. Hol&w.or& M L,. Tucker.G. A_ ancl Knapp, J E. (1986) PM Trans R. Sot Lond B. 314, 399. 1-m. Fry...% C (.,9.&f+ Ph~%hf?mJst.r;~ 19~.73.5 I81 Fry, S C (1986) Planta 169, 443 1.82 AJbersheun,. P ,. Da&ll,. G_ G.,. M&&d,. M_,. Vale& B...E.,. Sharp, J K, Nothnagel, E A., Davis, K R, Yumazaki, N, ~dlJJl,.~.I.,.b&,.u!

I83 147

Lang, W. C (1982) Plant Cell Phystol

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23, 1259

,..%rh1,.H_.aRd_ Ihaanl,. I_ $!!6~). Apr-

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Chem 29, 840 149 Kahl, G. (1978) m Blochemzstry of Wounded Plant Tzssue (Kahl, G., ed), p 347 de Gruyter, Berlin. 15Q Fukuda,~ H and Komammc- A (1982) Planta Ls-423. I51 Ishlda, A, Ono, K and Matsusaka, T. (1985) Plant Cell Rep 4, 54. 152 Imberty, A, Goldsberg, R and Catesson, A M (1985) Planta 164, 221

Van Huystee, R B. and Lobarzewskl (1982) Plant Scl Letters 21, 59. 156 Kevers, C., Stlcher, L., Penel, C, Greppm, H and Gaspar, Th (1985) Plant Growth Regul. 1, 61. 157 Mader, M and Walter, C (1986) Planta 169, 273 1%. Chlbb;ir,. & N. and Van. ti@ee,. R_ S. (.t_q%). .I Pbznr. Phystof. 123, 477 I59 Church, D L. and Galston, A. W (1987) Plant Physrol., Suppl 84,74 I60 Evans, J J (1987) PIant Physlol Suppl 84,41 l-41... Mellon,._. T F -. (19371 ~.-._ .... . Pht PhpioLSupp1. 84,. 140.. 142 Lagnmlm, L Mu and- Rothstem,~ So (L987) Plant P&ml Suppl 84, 108 163 Dey, P. M and Dixon, R. A. (1985) Blochemzstry of Storage Carbohydrates zn Green Plants Academic Press, London 164 Reid, J S G. (1985) in Btochemzstry of Plant Cell Walls (Brett, C T and Hdlman, J R., eds), p 259 Cambridge Umverslty Press, Cambridge. I65 Sexton, R, Durbm, M. L and Lewis, L N (1981) Plant Cell Envrr. 4, 67 166 Chnstofferson, R E, Tucker, M. L and Latles, G G (1984) Pfant Mol. Blol 3, 384. 167 Felix, G and Mems, F. Jr (1985) Planta 164, 429. I68 Keen, N. T and Yoslnkawa (1983) PIant Physlol 71,460. 169 Kombrmk, E and Hahlbrock, K. (1986) Plant Physlol 81,216 170 Boller, T, Gehrl, A, Maach, F and Vogeh, U (1983) Pfanta 157, 22. 171 Broghe, R , Coruzzl, G , Keith, B. and Chua, N. H (1984) Plant Mel Blol. 3, 431 172. Boiler, T. and Vogeh, U. (1984) Plant Physlol. 74, 442 173. Broghe, K E., Gaynor, J. J and Broghe, R M (1986) Prog Nat1 Acad SCI U S.A. 83,682O 174 Hubcr, D J and Nevms, D J. (1982) Planta 155, 467 I55

1249

of control

L&4.

185. 186

187

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Dell, A (1983) m Structure and Function of Plant Genomes (.C&!&. 0 a&_ Dl’111P& I_,. P&j,. p Z!1 Plenlun,. NPJV.York. Darvdl, A G and Albershelm, P (1984) Annu Reo Plant Phystol. 35, 243 &lhn,.n I ,_Dar_vdl,.~A_G .and AlhP&e~m,. P (.!%4). B.wl.. Cell 51, 275 York, W S , Darvill, A. G and Albershelm, P (1984) Plant Physlol 75, 295 Tran, T Van K, Toabart, P, Cousson, A_,~Darvrll,~ A C;,~ Golhn, D J, Chelf, P. and Albershelm, P (1985) Nature 314, 615 Pladys, D., Esquerre-Tugaye, M T and Touze, A (1981) Phytopathol. A. 102, 266.

Hanson, K. R and Havlr, E A (1981) The Btochemlstry of Plants, A Comprehensloe Treattse Vol 7 (Conn, E E. ed ), p. 577. Academic Press, New York 191 Harborne, J. B (1980) Encyclopaedta of Plant Physiology New Series 8, 332 l-92. I&odes,. M_ 1. and WdfNltlm,. L S ‘2 (LW%). In. The Blochenustry of Wounded Plant Tissue (Kahl, G, ed), p 243 de Gruyter, Berhn 193 Hahlbrock, K and Gnsebach, H (1979) Annu Reu Plant 190

Physzol 30, 105 L!!4. Dixon,. R A_,. np,y,. I? M_ and Lamb,. C 1 (J-9%3). Ad11 Enkymol~ R&ted Aleas M%l &nl S33i 1 195. Jones, D H (1984) Phytochemtstry 23, 1349. 196. Marsh, H V, Havlr, E A and Hanson, K R (1968) Btochemlstry 7, 1915. 197 Havir, E. A. and Hanson, K R (1973) Blochemlstry 12, 1583 198 Zimmerman, A and Hahlbrock, K. (1975) Arch. Biochem Blophys. 166, 54. 199 Bolwell, G P., Sap, J., Cramer, C. L, Lamb, C J., Schuch, W and Dixon, R. A (1986) Blochlm Blophys Acta 881, 210 200 Bolwell, G P., Bell, J N , Cramer, C. L , Schuch, W., Lamb, C J. and Dixon, R A. (1985) Eur J Blochem 149,411 201 Havlr, E A. and Hanson, K R (1986) Btochenustry 7,1904 202 Kuhn, D H, Chappell, J., Boudet, A. and Hahlbrock, K, (1984) Proc Natl Acad Scr, U S A. 81, 1102 203. Edwards, K., Cramer, C. L., Bolwell, G P, Dixon, R A, Schuch, W and Lamb, C J (1985) Proc Nat1 Acad Scl U.S A 81, 1102 204 Cramer, C. L , Edwards, K ,Dron, M., Liang, X , Bolwell, G P , Dixon, R , Schuch, W and Lamb, C J (1988) Proc. Nat2 Acad SCI U.S A (in press)

1250

205 206 201 208 209 210 211

212 213

214

215

216 217 218 219 220 221 222 223. 224 225 226 227 228 229 230 231 232 233 234 235

236 237

G P BOLWELL

Potts, J R M, Weklych, R and Con, E. E (1974) J Brol Chem 249, 5019 Rich, P R and Lamb, C. J (1977) Eur _I Btochem 72,353 Grand, C. (1984) FEES Letters 167, 7 Hagmann, M L and Grtsebach, H (1984) FEES Letters 175, 199 Hagmann, M L , Heller, W. and Grlsebach, H (1984) Eur J Blochem 142, 127 Gabrlac, B , Benvemste, I and Durst, F (1985) C R Acad .%I Parts 301, 753 HIgash], K, Ikeuchl, K, Obara, M , Karasakl, Y, Hlrano, H. Gotoh, S and Koya, Y (1985) Agrrc &o[ Chem 49, 2399 O’Keefe, D P, Romesser, J A, Leto, K J (1987) Recent Adv Phytochem (m press) Sesardq D , Boobls, A. R., McQuade, J , Baker, S , Lock, E A, Elcombe, C R , Robson, T T , Hayward, C and Davies, D S (1986) Blochem J 236, 569 Black, S D and Coon, M J (1986) m Cytochrome P-450 (Orttz de Montellano, P R., ed), p 161 Plenum, New York Nebert, D W , Adesmk, M , Coon, M J , Estabrook, R W, Gonzalez, F J . Guengench, P , Gunsalus, I C , Johnson, E F, Kemper, B , Levm, W, Phllhps, I R , Sato, R , Wateman, M R (1987) DNA 6, 1 Stafford, H A and Dresler, S (1972) Plant Physlol 49,590 Bolwell, G P and Butt, V S (1983) Phytochenustry 22,37 Butt, V S (1985) Annu Proc Phytochem Sot Europ 25, 349 Kamsteeg, J., van Brederode, J , Verschuren, P M and van Nlgtevecht, G (1981) Z Pfanzenphysrol. 102,435 Bomwell, J M and Butt, V S (1986) 2 Naturforsch 41c, 56 Mayer, A A (1987) Phytochenusrry 26, 11 Poulton, J E (1981) m The kochemrstry of Plants Vol 7 (Conn, E , ed), p 667 Academic Press, New York Poulton, J , Hahlbrock, K and Grlsebach, H (1977) Arch Brochem Blophys 180, 542 Poulton, J , Hahlbrock, K and Grlsebach. H (1976) Arch Btochem Blophys 173, 301 Poulton, J , Hahlbrock, K and Grlsebach, H (1976) Arch Blockem Blophys 176, 449 Knobloch, K H and Hahlbrock, K (1975) Eur J Biothem 52, 3 11 Knobloch, K H and Hahlbrock, K (1977) Arch Blochem. Bmphys 184, 237 Hemzmann, U and Seltz, IJ (1977) Planta 135, 313 Grand, C, Boudet, A and Boudet, A M (1983) Planta 158, 225 Kreuzaler, F and Hahlbrock, K (1975) Eur J Btochem. 56, 205 Kreuzaler, F and Hahlbrock, K (1975) Arch Btochem Blophys 169, 84 Saleh, N A M , Frltsch, H , Kreuzaler, F and Grlsebach, H (1978) Phytochemrstry 17, 183 Harborne, J B and Mabry, T J eds (1982) The Flavonords Advance7 m Research Chapman & Hall, London Beerhues, L and Wlermann, R (1985) Z Naturforsch. 40, 160 Hahlbrock, K ,Boudet, A M , Chappell, J , Kreuzaler, F , Kuhn. D N and Ragg., H (1982) m Structure and Function oj PIant Grnomes (Clfferl, 0 and Dure, L , eds), p 15 Plenum, New York Kreuzaler, F, Ragg, H, Fautz, E, Kuhn, D N and Hahlbrock, K (1983) Proc Nat1 Acad Set. US A 80,259l Ebel. J, Schmidt, W E and Loyal, R (1984) Arch Btochem

Blophyr 232, 240 Ryder, T B, Cramer, C L, Bell, J N, Robbms, M P, Dixon, R A and Lamb, C J (1984) Proc Natl Acad SCI L’S A 81. 5724 239 Bell, J N, Ryder. T B , Wmgate, V P M , Bailey, J A and Lamb, C J (1986) ~\fol Cell Blol 6 240 Ryder, T B. Hedrrck. S A. Bell, J N . Clause, S D and Lamb, C J (1988) Proc Narl Acud Scr U S A (m press) 241 Herrman, A (1987) Ph D Thesis, Koln 242 Kuhn, D N, Chappell, J and Hahlbrock, K (1982) rn Structure and Functmn of Plant Genomey (Clfferl, 0 and Dure, L, eds), p 329 Plenum, New York 243 Douglas, C, Hoffman, H Schulz, W and Hahlbrock, K (1987) EMBO J 6. 1189 244 Hoffman, H (1987) Ph D Thesis, Koln 245 Scheel, D, Dangl, J L, Douglas, C, Hauffe, K D, Herrman, A, Hoffman, H , Lozoya, E, Schulz W and Hahlbrock, K (1988) m Plant Molecular B~oloyy 1987 (von Wettstem, D. ed), NATO ASI Series (m press] 246 Lamb, C J and Rubery, P H (1976) Planta 130, 283 247 Lamb, C J (1979) Arch Bwchem bophys 192, 311 248 Billet. E E and Smith. H (1980) Phytochemlsrry 19, 1035 249 Dixon, R A, Brown. T and Ward, M (1980) Planta 150, 279 250 Amrhem. N and Goedekc, K H (1977) Plum Scrence Letter\- 8, 3 13 251 Amrhem. N and Gerhart, J (lY79) Blot/urn Bwphys Acra 53, 434 252 Lamb, C. J (1982) Plant Cell Enrwon 5, 471 253 Noe, W and Seltz, H U (1982) Planta 154,454 254 Johnson, C, Attrrdge, T and Smith, H (1975) Bzochlm &ophys Acta 385, 11 255 Lawton, M A, Dixon, R A and Lamb. C J (1980) Blochtm Blophys Acta 633. 162 256 Shields, S E. Wmgate, V P and Lamb. C J (1982) Eur J Blochem 123, 389 257 Bolwell. G P. Cramer, C L, Lamb, C J, Schuch. W and Dixon, R A (1986) Planta 169. 97 258. Bolwell, G P, Edwards, K, Mavandad, M , Mlllar, D, Schuch, W and Dixon, R A (1988) Phytochemrstry (m press) 259 Gerrlsh, C , Robbms, M P and Drxon, R A (1985) Plant Scl Letters 38, 23 260 McCalla, D R and Nelsh, A C (1959) Can J Bzochem Physzol 37. 537 261. Dixon, R A dnd Bolwell. G P (1986) m Secondary Metahohsm m Plant Tissue Culture3 (Morris, P , Scragg, A H , Stafford, A and Fowler, M W , eds). p 89 CambrIdge Umverslty Press, CambrIdge 261a Rasoolq, R and Somerville. S C (1986) Plant Phwwl Suppl 80, 43 262 DI Cosmo, F and Towers, G N H (1984) Ret Adv Phytochem 18. 97 263 Wyramblk, D and Grlsebach, H (1975) Eur J Blochem 59, 9 264 Wengenmayer, H , Ebel, J and Gnsebach, H (1976) Eur J kochem 65, 529 265 Gross, G G (1977) Recent Adv Phytochem 11, 141 266 Kutsukl. H ,Shimada, M and Hlguchl, T (1982) Phylachetmstry 21, 19 267 Sarm, F, Grand, G and Boudet. A M (1984) Eur _I Blochem 139, 259 268 Grand, C (1986) m CellWalls ‘86 (Vlan. B , Rels, D and Goldberg. R , eds), p 276 Universlte Pierre et Marie Cune, ParIs 269 Northcote, D H (1972) Annu Rer. Plant Physfol 23, 113 270 Fry, S C (19861 Oxford Surt~e!.r Plant Mel Blol. 2. 1 238

Synthesis

of cell wall components.

271. Badger, M. R (1985) Annu Rev. PIant Physrol 36,27. 272 Freudenberg, K (1965) Science 148, 595 273 Freudenberg, K (1968) m Constuutlon and Biosynthesw of Llgnrn (Klemzeller, A, ed ), p 45 Sprmger, Berhn 274 Mantles, B (1985) Annu. Proc Phytochem. Sot. Europ 25, 173 275. Fry, S C (1983) Planta 157, 111 276 Fry, S C (1984) Methods Enzymol. 107, 388. 277 Epstein, L and Lamport, D. T. A (1984) Phytochenustry 23. 1241 278 Cooper, J B , Chen, J A, van Holst. G-J and Varner, 3 E (1987) TIBS 12, 24. 279 Fry, S. C (1987) m Molecular and Physlologzcal Aspects of Plant Peroxrdases (Greppm, H., Penel, C and Gaspar, T , eds), p 162 Umverslty of Geneva Press 280 Lamport, D T A (1987) m Molecular and Physrologrcal Aspects of Plant Peroxidases (Greppm, H Penel, C. and Gaspar, T , eds), p 199 Umverslty of Geneva Press 281 Fry, S C (1987) J Expt. Botany 38, 853 282. Fry, S C (1987) Planta 171, 205 283 Borchert, R (1978) Plant Physlol. 62, 794. 284. Espehe, K E, Franceschl, V R and Kolattukudy, P E (1986) Plant Physrol 81, 487 285 Kolattukudy, P E (1980) Science 280, 990 286 Kolattukudy, P E (1981) Annu. Rev Plant Physlol 32,539 287 Sohday, C L and Kolattukudy, P E. (1977) Plant Phys~ol 59, 1116 288. Salaun, J P, Benvemste, I., ReIchart, D and Durst, F (1981) Eur J Blochem. 119, 651. P. E (1978) Arch Blochem 289 Sohday, C L. and Kolattukudy, Blophys 188, 338 290. Agrawal, V P and Kolattukudy, P E (1978) Arch Blothem Btophys 191,466. 291 Kaufman, P B, Daymandan, P., Takeoka, Y, Blgelow, W C , Jones, J D., Iber, R K (1981) m S&on and Sdlceous Structures m Blologrcal Systems (Simpson, I. L and Volcam, B E , eds), p 409 Springer, Berhn. 292 Weiss, A. and Herzog, A. (1978) m Blochemtstry of Skcon and Related Problems (Benz, G and Lmdqulst, I, eds), p 109. Plenum, New York 293 Hodson, M J., Sangster, A. G and Parry, D. W. (1984) Proc Roy Sot B222 427 294 Bell, A- A (1981) Annu. Rev Plant Physlol 32, 21 295 Perry, C C , Wllhams, R J P. and Fry, S C. (1986) J PIant Phystol 126, 437 296 Heath, M C and Stumpf, M. A (1986) Physlol. Mol Plant Path. 29, 27 297 Mueller, S C. and Brown, R. M (1980) J Cell &ol. 84,315 298 Glddmgs, T H , Brower, D L., Staehehn, L D (1980) J Cell B~ol 84, 327 299. Plckett-Heaps, J D and Northcote, D H (1966) J Exp Botany 17, 20 300. Bowles, D J and Northcote, D H. (1974) Blochem J 142, 139 301 Robmson, D. G , Eismger, W R., Ray, P. M (1976) Ber Dtsch Bot. Ges. 89, 147 302 Steer, M W. (1985) m Botamcal Muzroscopy 1985 (Robards, A W, ed), p. 129 Oxford Umverslty Press, Oxford 303 Fowke, L C , Renme, P. J and Constabel, F (1983) Plant Cell Rep 2, 292 304. McClean, B and Jumper, B E (1986) PIanta 169, 153 305 Staehlm, L A. and Chapman, R L. (1987) Planta 171, 43 306. Mersey, B. G, Gnffing, L. R, Renme, P J and Fowke, L C (1985) Planta 163, 317 307 Mersey, B G, Gaffing, L R and Fowke, L C. (1985) in

308 309 310 311 312. 313.

314. 315

aspects

of control

1251

The Physlologlcal Properties of Plant Protoplasts (Pilet, P E , ed), p. 45 Springer, Berlin Grlffing, L R, Mersey, B G and Fowke, L C (1986) Planta 167, 175. Colman, J. 0 D, Evans, D E, Hawes, C. R, Horsley, D, and Cole, L (1987) J Cell SCI 88, 35 Tanchak, M A, Grilling, L. R , Mersey, B G and Fowke, L C (1984) Planra 162, 481 Joachlm, S. and Robmson, D G (1984) Eur J Cell B~ol 34,212 Northcote, D. H. (1971) Symp Sot Exptl Blol. 25, 51 Northcote, D H (1977) m Cell Surface Reviews (Poste, G and Nicholson, G L, eds), p 77 North Holland, Amsterdam Herth, W (1980) J. Cell Blol 87, 442 Heath, I B. and Seagull, R. W (1982) m The Cytoskeleton m Plant Growth and Deuelopment (Lloyd, C W., ed.), p. 163 Academic Press. London

316. Gunning, B E S and Hardham, A R (1982) Annu Rev Plant Physlol. 33, 651 317 Falcolner, M and Seagull, R W. (1984) Protoplasma 125, 190 318 Falcolner, M and Seagull, R. W (1985) Protoplasma 128, 157. 319 Rodriguez-Boulan, E., Misek, D. E., Vega de Salas, D, Salas, P J. I and Bard, E (1985) Curr Topics Membr. Transp 24, 251 320 Robinson, D G (1985) Membranes Endo- and Plasmamembranes of Plant Cells Wiley, Chichester 321 Warren, G (1987) Nature 327, 17 322. Rothman, S. S (1985) Protem SecretIon A Crrtuzal Analysis of the Vesicle Model Wiley, Chichester 323 Von Hegne, G (1983) Eur. J Blochem. 133, I7 324. Baulcombe, D C, Martlenssen, R. A, Huttly, A. M, Barker, R F. and Lazarus, C M. (1986) Phd Trans Roy Sot. Lond B314,441 325. Key, J L, Kroner, P., Walker, J, Hong, J C, Ulnch, T. H , Amley, W. M, Gantt, J S and Nagao, R T (1986) Phd Trans Roy Sot Lond B314,427 326. Lamb, C J, Bell, J N., Cramer, C. L, Dddme, S L, Grand, C , Hednck, S A., Ryder, T B and Showalter, A M (1987) Beltsodle Agricultural Research Centre, Symposmm X, p 237. Martmus NiJhoff, Dordrecht 327 Staswlck P,Chnspeels, M J. (1985)J Mel Appl Genetrcs 2, 535 328. Kawasaki, S (1981) PIant Cell Phystol. 22, 431. 329 Northcote, D H (1983) Phd Trans Roy Sot. London. B300, 107 330 Robinson, D G., Andreae, M and Sauer, A (1985) m BIochemtstry of Plant Cell Walls (Brett, C T and Hillman, J. R , eds), p 155 Cambndge Umverslty Press, Cambridge 331 Stafford, H A (1981) m The Blochetmstry of Plants, A Comprehensrve Treatise Vol. 7 (Conn, E E, ed), p 117 Academic Press, New York. 332 Wagner, G J and Hrazdma, G. (1984) Plant Physlol. 74, 901 333 Hrazdma, G and Wagner, G J. (1985) Arch Blochem Blophys 237, 88 334 Ahbert, G., RanJeva, R and Boudet, A M. (1977) Phys~ol Veg. 15, 279 335 Czichl, U. and Kmdl, H (1977) Planta 134, 133 336 Zobel, A. M. (1986) Annu. Botany 57,801. 337. Ibrahlm, R K, De Luca, V., Khourl, H, Latchmlan, L, Bnsson, L. and Charest, P. M. (1987) Phytochemtstry 26, 1237 338 Brown, R. M. (1985) J Cell Ser. Suppl 2, 13

G P BOLWELL

1252 339 Halgler.

377

340

378

341

342. 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357

358 359 360

361 362 363

364 365 366 367 368 369 370 371 372. 373 374 375 376

C H and Brown, R M (1986) Protoplasmn 134, 111 Hodges, T K and MI&. D (1985) Methods Enzymol. 118, 41 Preston, R D (1986) m Cellulose Structure, Mahjicatlon and Hydrolysa (Young, R A and Rowe]], R M , eds), p 3 Wiley, Chichester Farquhar, M G (1983) Methods Enzymol 98, 1 Baydoun, E A -H and Northcote, D H (1980) J Cell SCI 45, 169 Baydoun, E A -H and Northcote, D H (1981) Bmchem J 193, 781 Bolwell, G P (1986) J Cell Scr 82, 187 Hepler, P K and Wayne, R (1985) Annu Rev. Plant Physrol 36, 391 Evans, M L (1985) CRC Crit Rev Plant SU 2, 317 Bevan, M W and Northcote, D H (1981) Planta 152,32 Theologls, A and Ray, P M (1982) Proc Nat1 Acad Scr USA 79,418 ZurIluh, L L and Gullfoyle,T J (1982) Phnt Physroi 69,332 Theologls, A, Huynh, T V and Davis, R W (1985) J Mel BlOl 183, 53 Theologls, A (1986) Annu Rev Plant Physrol 37, 407 Rubery, P H and Northcote, D H (1970) Blochim hophys Acta 222, 95 Asamlzu, T , Nakano, N and Nlshl, A (1983) Planta 158, 166 Inoue, H ,Yamamoto, R and Masuda, Y (1984) Plant Cell PhYSlOl 25, 1341 Masuda, Y (1985) B~ol PIant 27, 119 Masuda, Y (1985) m Elochemlstry of Plant Cell W&s (Brett, C T and Hlllman, J R, eds), p 270 Cambridge University Press CambrIdge Koyama, T , Hayash], T ,Kato, Y and Masuda, K (1981) PIant Cel[ Physlol 22, 1191. Montague, M J and Ikuma, H (1975) Plant Physlol 55, 1043 Adams, P A, Montague, M J, Tepfer, M, Rayle, D L, Ikuma, H and Kaufman, P B (1975) PIant Phys~ol 56, 157 Stuart, D A and Jones, R L (1977) PIant Phystol 59, 61 Fry, S C (1979) Planta 146, 343 Roberts, L W (1976) Cytodrfferentratlon rn Plants Xylogenexs ah a Model System Cambridge Umverslty Press, Cambridge Phdhps, R (1980) Perspectives m Plant rlasue Cultures, Int Ret Cyfol Academic Press, New York Fukuda, H and Komamme, A (1980) Plant Ph~s~ol 65,57 Dodds. J H (1980) 2 Pflanzenphyslol 99, 283 Fukuda, H and Komamme, A. (1980) Plant Physrol 65,61 Fukuda, H and Komamme, A (1981) Plant Cell Physlol. 22, 41. Fukuda, H and Komamme, A (1982) Planta 155,423 Dalessandro, G and Northcote, D H (1977) Phytochenustry 16, 853 Mmocha, S C and Halperm, W (1976) Can J Botany 54, 79 Simpson, S F and Torrey, J G. (1977) Plant Physlol 59,4 Miller, A R and Roberts, L. W (1984) J Exp Botany 154, 691 Haddon, L E and Northcote, D H (1975) J Cell Scl 17, 11 Bolwell, G P and Northcote, D. H (1981) Planta 192,325 Everett, N P, Wach, M and Ashworth, D J (1985) Plant Ser. 41, 133

379 380

381

382 383 384 385 386 387 388 389 390 391

392

393 394 395 396 397 398 399

400 401 402 403 404 405

406 407 408 409

Kubol, T and Yamada, Y (1978) B&urn Blophys Acta 542, 181 Jones, D H and Northcote. D H (1981) Eur J Bkochem 116, 117 Bolwell, G P and Northcote. D H (1983) Blochem J 210, 509 Ozekl, Y and Komamme, A (1985) m Prrmary and Secondary Meraholrsm of Plant Cell Cultures (Neumann, K -H , Barz, W and Remhard, E , eds), p 100 Springer, Berlin Mems, F (1982) m Molecular Rmlogy of Plant Tumours (Kahl, G and Schell. J S . eds), p 3 Academic Press, New York Bevan, M W and Northcote, D H (1979) J Cell Scr 39. 339 Sung, Z R and Oklmoto, R (1981) Proc Natl Acad SLI U S A 78, 3683 Ammo, S and Komamme, A (1985) Plunr Cell Physro/ 26, 745 Ammo, S and Komamme, A (1985) Ph~~zol Plant 64,202 SchoW, F, Baumann. G , Raschke, E and Bevan, M W (1986) Proc R Sot Land B314.453 Gershenzon, J (1984) Ret Adt Phyrochem 18. 274 Boffey, S A and Northcote. D H (1975) Bwchem J 150, 433 Jaffe, M J , Huberman, M., Johnson, J and Telewskl F W (1985) Plant Phyczol 77, 722 Kahl, G , ed (1978) The Bmthemtstry of Wounded PIant Tissues de Gruyter, Berlin Kahl, G (1982) m Molecular B~oloyg of Plant Tumours (Kahl, G and Schell, J S . eds), p 211 Academic Press, New York, London B (1985) m Btology and Molecular hrology of Ward, E Plant-Pathogen Interactrons (Bailey, J A ed ). p 107 NATO ASI Series Plenum, New York Koepowltz, H , Dhyae, R and Fosket, D E (1975) J Eup Botany 26, 13 1 Roblin, G (1985) Plant Cell Physrol 26, 455 Roblm, G and Bonneman, A (1985) PIanr Cell Phyrml 26, 1273 Rmcon, M and Hanson, J B (1986) Physml Plant 67. 576 Verrter, B, Muller, D, Bravo. R and Muller, R (1986) EMBO J 5,913 Morgan J I. and Curran, T (1986) Nufure 322, 552 Yang, S F and Pratt, H K (1978) m &ochenustry o-f Wounded Plant 7issuec (Kahl. G . ed ). p, 596 de Gruyter. Berlin Boiler, Th and Kende, H (1980) Nature 286, 259 Kende, H and Boller, Th (1981) PLmta 151, 476 Yang, S F and Hoffman, N E (1984) Annu Rev Plant Phys1oI 35, 155 Nichols, S E and Latles. G G (1984) Plant Mel L31ol 3, 393 Nichols, S E and Latles. G G (1985) Plant Physrol 77. 753. Sadava, D and Chrispeels, M J (1978) m Bwchemutry of Wounded Plant T~ssuec (Kahl, G , ed ). p 85 de Gruyter. Berlm Roby, D , Toppan, M T. Esquerre-Tugaye. M T (1986) PIant Phy~~ol 81, 228 Abeles, F B and Forrence. L E (1970) Plant Physrol 45, 395 Tucker, M L, Lewis, L N, Durbm, M L and Clegg, M T (1987) P/ant Physlol suppl. 84, 108 Halverson, L. J and Stacey, G (1986) Mwrobrol Rev 50, 193

Synthesis

410 411

412

413 414 415 416 417 418 419

420

421 422 423 424

425.

426.

427

of cell wall components.

Heath, M C (1980) Annu Rev Phytopathology 18, 211 Hargreaves, J. A and Keon, J P R (1986) m Biology and Molecular Biology of Plant-Pathogen lnteractrons (Bailey, J , ed), p 134 NATO ASI series Springer, Berhn O’Connell, R J. and Bailey, J A. (1986) m Biology and Molecular Btofogy of Plant-Pathogen Interactions (Bailey, J , ed), p 39 NATO ASI series Sprmger, Berhn Street, P F S, Robb, J and Elhs, B. E (1986) Protoplasma 132, 1 Kauss, H and Jebhck, W. (1986) PIant Science 43, 103 Kauss, H and Jebhck, W (1986) PIant Physlol SO, 7 Sugawara, S , Inamoto, Y and Ushglma, M. (1981) Agrrc. Blol Chem 45, 1767 S.&he&L., Pp.%& C: & Greppm, H (l_%t_!.J C& Scr 4%. 345 Morns, M R and Northcote, D H (1977) Blochem J 166, 603 Dixon, R A, Bailey, J A., Bell, J N, Bolwell, G P, Cramer, C L, Edwards, R., Hamdan, M. A. M S., Lamb, C J, Robbms, M P, Ryder, T B. and Schuch, W (1986) Phil Trans R Sot. Land 8314,411. Showalter, A M, Bell, J N, Cramer, C. L., Bailey, J A, Yar~r, J E and LambT C I (1985) Prac_ Natl Acad SCI US A 82,655l Doke, N (1983) Physrnl Plant Pathol 23,345. Lynch, D. V and Thompson, J E (1984) FEES Letters 173, 251 Epperlem, M M , Noronha-Dutra, A. A. and Strange, R N (1986) Physlol Mol Plant Path01 28, 67 E&, _I.,%&, TkI B ZUKItih_mrdt, W E (1985) m Primary and Secondary Metabohsm of Plant Cell Cultures (Neumann, K -H., Barz, W and Remhard, E, eds), p 247 Sprmger, Berlin Ccamer, C_ L., Bell, J N , Ryder, T B, B&y, .I. A ~Schuch W , Bolwell, G P, Robbms, M. P, Dixon, R A and Lamb, C. J (1985) EMBO J. 4, 285 Kombrmk, E, Bollmann, J., Haffe, K. D, Knogge, W., Scheel, D., Schmeltzer, E ,Somsslch, I and Hahlbrock, K (1986) m Biology and Molecular Btology of Plant-Pathogen Interactions (Badey, J., ed ), p 254 Springer, Berhn Hadwlger, L A, Damels, C , Frlstensky, B W., Kendra, D

428 429 430 431.

432. 433. 434

435

436 437 438 439. 440 441 442 443. 444

445

aspects

of control

1253

F. and Wagoner, W (1986) m Biology and Molecular Biology of Plant-Pathogen InteractIons (Badey, J , ed ), p 263. Sprmger, Berlin Chappell, J. and Hahlbrock, K (1984) Nature 311, 76 Schmeltzer, E , Somsslch, I and Hahlbrock, K. (1985) Plant Cell Rep. 4, 293 Mazau, D and Esquerr&Tugaye’, M T (1986) Physlol Mol Plant Pathol 29, 147. Mazau, D , Rumeau, D. and EsquerrBTugaye’, M T (1986) m Brology and Molecular Biology of Plant-Pathogen mteractlons (Badey, J , ed.), p 245 Springer, Berhn Plerpomt, W. S (1986) Phytochevustry 25, 1595 Somsslch, I., Schmelzer, I and Hahlbrock, K (1986) Proc N&1 &ad .xU. U s A_ ax, 24.2’1 Esquerr&Tugayt, M T ,Mazau, D , Pehssler, B., Roby, D , Rumeau, D. and Toppan, A (1985) m Cellular and Molecular Biology of Plant Stress (Key, J and Kosuge, T ,eds), p. 459 Alan R LISS, New York Ecker, J R and Davis, R. W (1986) Molecular Biology of Plant Growth Control (Fox, J. E and Jacobs, M, eds), UCLA Symposia New Senes Vol. 44, 1 Alan R Llss, New York Schm&, W E a& Eb& I_ (1984) Proc Nntl had Set u.s A 84,4117 Darv& A G and Albershem, P (1984) Annu Rev Plant Physlol 35, 243 Dixon, R A (1986) Btol Rev 61, 239 Tomlyama, H., Okamoto, H, Katal, K (1983) Physlol Plant Path. 22, 233 Hattart_T andOh&Y (1985)PlantCellPhyslol 26,LlOt Pehssler, B , Thlbaud, J B , Gngnou, C. and Esquerre’Tugaye’, M T (1986) Plant Scl 46, 103. Baydoun, E A -H and Fry, S. C. (1985) Planta 165, 269 Davis, K R, Darvdl, A G and AIbershe~ P (t9986) Plant Molec &ol 6, 23. Collmer, A. (1986) m Biology and Molecular Biology of Plant-Pathogen Interactions (Bailey, J., ed ), p 277. Sprmger, Berlin Atkmson, M M , Baker, C J and Collmer, A. (1986) Plant Physlol 82, 142.