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Detection of γ-Aminobutyric Acid Transaminase Activity in Wheat Embryos
Biochem. Physiol. Pflanzen 180, 629-633 (1985)
Short Communication
Detection of y-Aminobutyric Acid Transaminase Activity in Wheat Embryos L. GALLESCHI, G. LAZZERI, C. SPANO, A. CAPOCCHI and C. FLORIS Dipartimento di Scienze Botaniche, Universita di Pisa, Italia Key T erm Index: y-aminobutyric acid, y-aminobutyrate transaminase, germination; Triticum durum
Summary y-aminobutyrate transaminase was detected in isolated wheat embryos. The enzymatic activity is present in the dry embryos and increases moderately during early germination. The transamination of GABA is three times more active with pyruvate than with 2-ketoglutarate as substrates. The optimum pH of the enzyme is 8.5. The results are considered in relation to the possible meaning of the y-aminobutyrate shunt in plants.
y-aminobutyric acid (GABA) is probably ubiquitous in higher plants, where it is formed by glutamic acid decarboxylation catalysed by L-glutamate decarboxylase (DIXON and FOWDEN 1961). Several reports demonstrated that GABA can enter the Krebs' cycle (INATOMI and SLAUGHTER 1971; DIXON and FOWDEN 1961) after transamination to succinic semi aldehyde which in turn is oxidized to succinate (STREETER and THOMPSON 1972). This pathway, called GABA-shunt, has been characterized in several plants, like Lupinus albus (ANDRES et al. 1973), Raphanus sativus (STREETER and THOMPSON 1972) and Triticum durum (GALLESCHI et al. 1976, 1978). In particular, T. durum embryos exhibit high levels of L-glutamate decarboxylase and succinic semialdehyde dehydrogenase activities during the seed ripening and the germination process (GALLEscHI et al. 1975, 1980). However, the GABA-transaminase activity (GABA-T ; EC 2.6.1.19) has not yet detected in Gramineae, and this paper concerns about some properties of this enzyme extracted from T. durum embryos. Triticum durum c.v. Cappelli embryos were used as enzymatic source. After sterilization of caryopses, 250 embryos were hand isolat ed and immediately homogenized in a cold mortar with 5 ml of 0.1 M phosphate buffer pH 7. 3 containing 1% Triton X-lOa (vol/vol), 0.2 mM EDTA and 1 mM mercaptoethanol. The homogenate was filtered through miracloth and then centrifuged at 12,000 x g for 20 min. The recovered supernatant was dyalized overnight, in cold room, against 0.01 M phosphate aptoethanol. After dialysis, the extracts, centrifuged in a bench buffer pH 8.0 containing 1 m M merc centrifuge, w ere utilized either for the enzymatic assay or for th e determination of total proteins by the modified Lowry's m ethod (BENSADOUN and WEINSTEIN 1976). GABA-T activity was measured in accord to the method describ ed by STREE TER and THOMPSON (1972) by utilizing borate buffer Abbreviations: GABA, y-aminobutyric acid; GABA-T, GABA transaminase
630
L. GALLESCHl et a!.
15,000
E a. c.:i
10,000
~
I-
>
IU
<
0 0
<
a:
5,000
7.0
9.0
8.0
10.0
pH Fig. 1. Dependence of GABA-T activity on pH. 0.1 M sodium phosphate buffer (.); 0.1 M glycine-NaOH buffer
(~);
0.1 M borate buffer (*).
pH 8.5 (60.umol), pyridoxal 5' phosphate (O.Ol.umol), mercaptoethanol (5.umol), cold GABA (5 ,umol) plus 14C-GABA (2.15 x 10-3 .umol; 0.5.uCi) pyruvate or 2-ketoglutaratec 5.umol) and the enzymatic extract (0.2 ml). The total volume of the reaction mixture was 1.020 m!. The controls were performed by omitting pyruvate or 2-ketoglutarate. The incubation was carried out at 30°C for 90 min and the enzymatic reaction immediately interrupted by eluting the reaction mixture through Dowex50 W columns (5 cm x 1.3). The radioactive succinic semialdehyde was evaluated in the eluate. The recovery of labeled succinic semialdehyde was similar to that described by STREETER and THOMPSON (1972).
Previous attempts failed to demonstrate the presence of GABA-transaminase in wheat seedlings, even after concentration of protein by ammonium sulphate precipitation (RIJVEN 1960). On the contrary, other reports describe the presence of this enzyme in dicotyledonous seeds (DIXON and FOWDEN 1961; ANDRES et al. 1973) and leaves (STREETER and THOMPSON 1972). Our results corroborate the presence of GABA-T activity in dry and germinating embryos of T. durum, although only low activity was
631
GABA Transaminase in Wheat
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I- a. (.)
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.......
~E
CLci
2,000
(/) c.:
1,000
o
6
12
18
HOURS
AFTER
24
30
IMBIBITION
Fig. 2. GABA-T activity during early seed germination.
demonstrated. The transamination of GABA is 3 times more active using pyruvate as amino group acceptor than 2-ketoglutarate. Similar results were obtained in Arachis cotyledons and Raphanus leaves, in which there was 5 and 19 times, respectively, as much transaminase activity with pyruvate as with 2-ketoglutarate (DIXON and FOWDEN 1961; STREETER and THOMPSON 1972). Thus this characteristic seems to be a common property of the higher plant GABA-transaminases till now studied. In fungi, 2-ketoglutarate is a better acceptor than pyruvate (BALDY 1972), while in mammals and bacteria the GABA-transaminases are specific only for 2-ketoglutarate (ROBERTS and BREGOFF 1953; SCOTT and JAKOBY 1959). As emphasised by STREETER and THOMPSON (1972) the transamination of GABA with pyruvate could have a physiological meaning in higher plants. However, a better knowledge of GABA-T properties in plants is needed to support this hypothesis. Exhaustive dialysis of wheat embryo GABA-T does not produce appreciable loss of enzymatic activity and the addition of exogenous pyridoxal-5'-phosphate does not increase the activity. GABA-transaminases of bacteria and fungi show similar properties (SCOTT and JAKOBY 1959; BALDY 1976). Optimal pH value of wheat embryo GABA-T is near 8.5 (Fig. 1) in accord to the pH values obtained for the Raphanus (STREETER and THOMPSON 1972) and bacterial enzyme (SCOTT and JAKOBY 1959). GABA-T is present in dry embryos; when its activity is
632
L. GALLESCHl et al.
evaluated during seed germination, it shows a slight increase at 12 h and then decreases up to the dry seed values in the following imbitition times (Fig. 2). These and previous results confirm the presence of all the GABA-shunt enzymes in the wheat embryo (GALLESCHI et al. 1976, 1978). The presence of GABA-shunt enzymes has been also demonstrated for dry and germinating Lupinus albus seeds (ANDRES et al. 1973); the pathway is also operative in Sinapsis alba seeds during germination (VANDEWALLE and OLSSON 1983). In conclusion, the GABA-shunt seems to be a metabolic pathway present in seeds of Dicotyledons and Monocotyledons, in which it would be operative during early imbibition and the following germination, as it has been confirmed by the pattern of some enzymatic activities and by the experiments which utilize labeled precursors (VANDEWALLE and OLSSON 1983). However, other work to demonstrate this exciting hypothesis is needed. Aclrnowledgements The authors wish to thank Mr. F. SAVIOZZI for technical assistance and Mrs. P. ANDOLFI for typing the manuscript. This work was supported by Consiglio Nazionale delle Ricerche, Roma (n. 84.00737.04).
References ANDRES, 1., GONZALES, P., and SANTOS-RuIZ, A.: The presence and the influence of germination on the y-aminobutyrate pathway in Lupinus albus seeds. Physiol. Chern. and Physics 5, 357-364 (1973). BALDY, P.: Metabolisme de l'acide y-aminobutyrique dans les carpophores d' Agaricus bisporus LGE. Etude preliminaire de la y-aminobutyrate: a-cetoglutarate aminotransferase et de la semialdehyde succinate: NADP(P) oxydoreductase. C.R. Acad. Sc. Paris 275, 2877-2880 (1972). BALDY, P.: Metabolisme du y-aminobutyrate chez Agaricus bisporus LGE. II La y-aminobutyrate: a-cetoglutarate aminotransferase. Planta 130, 275-281 (1976). BENSADOUM, A., and WEISTEIN, D.: Assay of proteins in the presence of interfering materials. Anal. Biochem. 70,241-250 (1976). DIXON, R. O. D., and FOWDEN, 1.: y-aminobutyric acid metabolism in plants. Part. 2. Metabolism in higher plants. Ann. Bot. 25, 513-530 (1961). GALLES CHI, L., FLORIS, C., MELETTI, P., and COZZANI, 1.: On the location of glutamate decarboxylase in the caryopsis of hard wheat (Triticum durum) and its activity during early germination. Experientia 31, 28-29 (1975). GALLES CHI, L., SGARRELLA, F., FLORIS, C., TOZZI, M. G., and COZZANI, 1.: Inhibition by ATP and other regulatory properties of glutamate decarboxylase from wheat embryos. Bull. Mol. BioI. Med. 1, 107-118 (1976). GALLESCHI, L., TOZZI, M. G., COZZANI, 1., and FLORIS, C.: Succinic semialdehyde dehydrogenase of wheat grain. Planta 142, 175-180 (1978). GALLESCHI, L., FLORIS, C., and MELETTI, P.: Succinic semialdehyde dehydrogenase activity in durum wheat during physiological phases of seed ripening. Biochem. Physiol. Pflanzen 175, 87-90 (1980). INATOMI, K., and SLAUGHTER, J. F.: The role of glutamate decarboxylase and y-aminobutyric acid in germinating barley. J. Exp. Bot. 22, 561-571 (1971). RIJVEN, A. H. G. C.: On the utilization of y-aminobutyric acid by wheat seedlings. Australian J. BioI. Sci. 13, 132-141 (1960).
GABA Transaminase in Wheat
633
ROBERTS, E., and BREGOFF, H. M. : Transamination of y-aminobutyric acid and B-alanine in brain and liver. J. BioI. Chern. 201, 393-398 (1953). SCOTT, E. M., and JAKOBY, W. B.: Soluble y-aminobutyric-glutamic transaminase from Pseudomonas fluorescells. J. BioI. Chern. 234, 932-936 (1959). STREETER, J. G., and THOMPSON, J. F.: In vivo and in vitro studies on y-aminobutyric acid metabolism with the radish plant (Raphanus sativus L.). Plant Physiol. 49, 579-584 (1972). VANDE WALLE, 1., and OLSSON, R.: The y-aminobutyric acid shunt in germinating Sinapsis alba seeds. Plant Sci. Lett. 31, 269-273 (1983).
Received April 18, 1985; accepted May 13, 1985 Author's address: L. GALLES CHI, Dipartimento di Scienze Botaniche, Universita di Pisa, Pisa, Ita.Iia.
Biochem. Physiol. Pflanzen 180, 633 - 635 (1985)
Buchbesprechungen MENGEL, KONRAD: Ernahrung und Stoffwechsel der Pflanz e. 6. iiberarb. Auflage. 431 Seiten, 158 Abbildungen, 16 teils farbi ge Tafeln, 97 Tabellen. VEB Gustav Fischer Verlag, Jena 1984. Preis : L einen DDR 34,00 M; Ausland 39,00 Dl'IL Auch die vorliegende 6. Auflage des " Mengel" behalt die bisherige Dreiteilung des Stoffgebietes bei, namlich in 1. Biochemic wichtiger Stoffwechselvorgange, 2. Erniihrungs- und Ertragsphysiologie und 3. Spezielle Wirkung und Bedeutung der einzelnen Pflanzennahrstoffe. Der 1. Teil behandelt zunachst chemische Bindung, Sorption und enzymatische Reaktionen, urn danach auf dieser Grundlage Energie- und Kohlenhydratstoffwechsel, Lipidstoffwechsel sowie den Stoffwechsel der NVcrbindungen zu bcschreiben. Er wurde gegeniiber der 5. Auflage am stiirksten iiberarbeitet. Dies betrifft nicht nur die Anwendung der IUPAC-Nomenklatur, sondern auch die Einordnung bestimmt er, in der vorigen Auflage selbst andig ausgewiesener Teilgebiete. So wird die Abrufung der genetischen Information beim N-Stoffwechscl besprochen, wahrend der Feinbau der Zelle sowie die Phytohormone und Wirkstoffe jetzt im Teil 2 (Ernahrungs- und Ertragsphysiologie) erscheinen. 1m 2. Tail widmet sich der Autor zunachst der Charakterisierung der Pflanzennahrstoffe, dem Boden als Nahrmedium der hiiheren Pflanze und der Stoffaufnahme bzw. dem Stofftransport. Es foJ gen Abschnitte iiber Wuchsstoffe, Wachstumsregulatoren und Biozide sowie iiber die Beziehungen zwischen Erniihrung bzw. Diingung einerseits und Ertragsbildung bzw. Qualitat pflanzlicher Produkte andererseits. Neu aufgenommen wurden Teilabschnitte iib er Wurzelwachstum und -morphologie, Rhizosphare und Mykorrhiza sowie Nitrifikationsinhibitoren. Der 3. Teil befaBt sich mit den fiir Pflanzen bedeutsamen chemischen Elementen. Es werden im einzelnen Vorkommen, Kreislauf in der Natur (soweit Kenntnisse vorhanden), Aufnahme und Vert eilung bei Pflanzen sowie Fragen der Ernahrung und Diingung besprochen. Der Verfasser nimmt
Short Communication
Detection of y-Aminobutyric Acid Transaminase Activity in Wheat Embryos L. GALLESCHI, G. LAZZERI, C. SPANO, A. CAPOCCHI and C. FLORIS Dipartimento di Scienze Botaniche, Universita di Pisa, Italia Key T erm Index: y-aminobutyric acid, y-aminobutyrate transaminase, germination; Triticum durum
Summary y-aminobutyrate transaminase was detected in isolated wheat embryos. The enzymatic activity is present in the dry embryos and increases moderately during early germination. The transamination of GABA is three times more active with pyruvate than with 2-ketoglutarate as substrates. The optimum pH of the enzyme is 8.5. The results are considered in relation to the possible meaning of the y-aminobutyrate shunt in plants.
y-aminobutyric acid (GABA) is probably ubiquitous in higher plants, where it is formed by glutamic acid decarboxylation catalysed by L-glutamate decarboxylase (DIXON and FOWDEN 1961). Several reports demonstrated that GABA can enter the Krebs' cycle (INATOMI and SLAUGHTER 1971; DIXON and FOWDEN 1961) after transamination to succinic semi aldehyde which in turn is oxidized to succinate (STREETER and THOMPSON 1972). This pathway, called GABA-shunt, has been characterized in several plants, like Lupinus albus (ANDRES et al. 1973), Raphanus sativus (STREETER and THOMPSON 1972) and Triticum durum (GALLESCHI et al. 1976, 1978). In particular, T. durum embryos exhibit high levels of L-glutamate decarboxylase and succinic semialdehyde dehydrogenase activities during the seed ripening and the germination process (GALLEscHI et al. 1975, 1980). However, the GABA-transaminase activity (GABA-T ; EC 2.6.1.19) has not yet detected in Gramineae, and this paper concerns about some properties of this enzyme extracted from T. durum embryos. Triticum durum c.v. Cappelli embryos were used as enzymatic source. After sterilization of caryopses, 250 embryos were hand isolat ed and immediately homogenized in a cold mortar with 5 ml of 0.1 M phosphate buffer pH 7. 3 containing 1% Triton X-lOa (vol/vol), 0.2 mM EDTA and 1 mM mercaptoethanol. The homogenate was filtered through miracloth and then centrifuged at 12,000 x g for 20 min. The recovered supernatant was dyalized overnight, in cold room, against 0.01 M phosphate aptoethanol. After dialysis, the extracts, centrifuged in a bench buffer pH 8.0 containing 1 m M merc centrifuge, w ere utilized either for the enzymatic assay or for th e determination of total proteins by the modified Lowry's m ethod (BENSADOUN and WEINSTEIN 1976). GABA-T activity was measured in accord to the method describ ed by STREE TER and THOMPSON (1972) by utilizing borate buffer Abbreviations: GABA, y-aminobutyric acid; GABA-T, GABA transaminase
630
L. GALLESCHl et a!.
15,000
E a. c.:i
10,000
~
I-
>
IU
<
0 0
<
a:
5,000
7.0
9.0
8.0
10.0
pH Fig. 1. Dependence of GABA-T activity on pH. 0.1 M sodium phosphate buffer (.); 0.1 M glycine-NaOH buffer
(~);
0.1 M borate buffer (*).
pH 8.5 (60.umol), pyridoxal 5' phosphate (O.Ol.umol), mercaptoethanol (5.umol), cold GABA (5 ,umol) plus 14C-GABA (2.15 x 10-3 .umol; 0.5.uCi) pyruvate or 2-ketoglutaratec 5.umol) and the enzymatic extract (0.2 ml). The total volume of the reaction mixture was 1.020 m!. The controls were performed by omitting pyruvate or 2-ketoglutarate. The incubation was carried out at 30°C for 90 min and the enzymatic reaction immediately interrupted by eluting the reaction mixture through Dowex50 W columns (5 cm x 1.3). The radioactive succinic semialdehyde was evaluated in the eluate. The recovery of labeled succinic semialdehyde was similar to that described by STREETER and THOMPSON (1972).
Previous attempts failed to demonstrate the presence of GABA-transaminase in wheat seedlings, even after concentration of protein by ammonium sulphate precipitation (RIJVEN 1960). On the contrary, other reports describe the presence of this enzyme in dicotyledonous seeds (DIXON and FOWDEN 1961; ANDRES et al. 1973) and leaves (STREETER and THOMPSON 1972). Our results corroborate the presence of GABA-T activity in dry and germinating embryos of T. durum, although only low activity was
631
GABA Transaminase in Wheat
>-
I-
c:: Q)
>'0....
I- a. (.)
«'0
~E ~
.......
~E
CLci
2,000
(/) c.:
1,000
o
6
12
18
HOURS
AFTER
24
30
IMBIBITION
Fig. 2. GABA-T activity during early seed germination.
demonstrated. The transamination of GABA is 3 times more active using pyruvate as amino group acceptor than 2-ketoglutarate. Similar results were obtained in Arachis cotyledons and Raphanus leaves, in which there was 5 and 19 times, respectively, as much transaminase activity with pyruvate as with 2-ketoglutarate (DIXON and FOWDEN 1961; STREETER and THOMPSON 1972). Thus this characteristic seems to be a common property of the higher plant GABA-transaminases till now studied. In fungi, 2-ketoglutarate is a better acceptor than pyruvate (BALDY 1972), while in mammals and bacteria the GABA-transaminases are specific only for 2-ketoglutarate (ROBERTS and BREGOFF 1953; SCOTT and JAKOBY 1959). As emphasised by STREETER and THOMPSON (1972) the transamination of GABA with pyruvate could have a physiological meaning in higher plants. However, a better knowledge of GABA-T properties in plants is needed to support this hypothesis. Exhaustive dialysis of wheat embryo GABA-T does not produce appreciable loss of enzymatic activity and the addition of exogenous pyridoxal-5'-phosphate does not increase the activity. GABA-transaminases of bacteria and fungi show similar properties (SCOTT and JAKOBY 1959; BALDY 1976). Optimal pH value of wheat embryo GABA-T is near 8.5 (Fig. 1) in accord to the pH values obtained for the Raphanus (STREETER and THOMPSON 1972) and bacterial enzyme (SCOTT and JAKOBY 1959). GABA-T is present in dry embryos; when its activity is
632
L. GALLESCHl et al.
evaluated during seed germination, it shows a slight increase at 12 h and then decreases up to the dry seed values in the following imbitition times (Fig. 2). These and previous results confirm the presence of all the GABA-shunt enzymes in the wheat embryo (GALLESCHI et al. 1976, 1978). The presence of GABA-shunt enzymes has been also demonstrated for dry and germinating Lupinus albus seeds (ANDRES et al. 1973); the pathway is also operative in Sinapsis alba seeds during germination (VANDEWALLE and OLSSON 1983). In conclusion, the GABA-shunt seems to be a metabolic pathway present in seeds of Dicotyledons and Monocotyledons, in which it would be operative during early imbibition and the following germination, as it has been confirmed by the pattern of some enzymatic activities and by the experiments which utilize labeled precursors (VANDEWALLE and OLSSON 1983). However, other work to demonstrate this exciting hypothesis is needed. Aclrnowledgements The authors wish to thank Mr. F. SAVIOZZI for technical assistance and Mrs. P. ANDOLFI for typing the manuscript. This work was supported by Consiglio Nazionale delle Ricerche, Roma (n. 84.00737.04).
References ANDRES, 1., GONZALES, P., and SANTOS-RuIZ, A.: The presence and the influence of germination on the y-aminobutyrate pathway in Lupinus albus seeds. Physiol. Chern. and Physics 5, 357-364 (1973). BALDY, P.: Metabolisme de l'acide y-aminobutyrique dans les carpophores d' Agaricus bisporus LGE. Etude preliminaire de la y-aminobutyrate: a-cetoglutarate aminotransferase et de la semialdehyde succinate: NADP(P) oxydoreductase. C.R. Acad. Sc. Paris 275, 2877-2880 (1972). BALDY, P.: Metabolisme du y-aminobutyrate chez Agaricus bisporus LGE. II La y-aminobutyrate: a-cetoglutarate aminotransferase. Planta 130, 275-281 (1976). BENSADOUM, A., and WEISTEIN, D.: Assay of proteins in the presence of interfering materials. Anal. Biochem. 70,241-250 (1976). DIXON, R. O. D., and FOWDEN, 1.: y-aminobutyric acid metabolism in plants. Part. 2. Metabolism in higher plants. Ann. Bot. 25, 513-530 (1961). GALLES CHI, L., FLORIS, C., MELETTI, P., and COZZANI, 1.: On the location of glutamate decarboxylase in the caryopsis of hard wheat (Triticum durum) and its activity during early germination. Experientia 31, 28-29 (1975). GALLES CHI, L., SGARRELLA, F., FLORIS, C., TOZZI, M. G., and COZZANI, 1.: Inhibition by ATP and other regulatory properties of glutamate decarboxylase from wheat embryos. Bull. Mol. BioI. Med. 1, 107-118 (1976). GALLESCHI, L., TOZZI, M. G., COZZANI, 1., and FLORIS, C.: Succinic semialdehyde dehydrogenase of wheat grain. Planta 142, 175-180 (1978). GALLESCHI, L., FLORIS, C., and MELETTI, P.: Succinic semialdehyde dehydrogenase activity in durum wheat during physiological phases of seed ripening. Biochem. Physiol. Pflanzen 175, 87-90 (1980). INATOMI, K., and SLAUGHTER, J. F.: The role of glutamate decarboxylase and y-aminobutyric acid in germinating barley. J. Exp. Bot. 22, 561-571 (1971). RIJVEN, A. H. G. C.: On the utilization of y-aminobutyric acid by wheat seedlings. Australian J. BioI. Sci. 13, 132-141 (1960).
GABA Transaminase in Wheat
633
ROBERTS, E., and BREGOFF, H. M. : Transamination of y-aminobutyric acid and B-alanine in brain and liver. J. BioI. Chern. 201, 393-398 (1953). SCOTT, E. M., and JAKOBY, W. B.: Soluble y-aminobutyric-glutamic transaminase from Pseudomonas fluorescells. J. BioI. Chern. 234, 932-936 (1959). STREETER, J. G., and THOMPSON, J. F.: In vivo and in vitro studies on y-aminobutyric acid metabolism with the radish plant (Raphanus sativus L.). Plant Physiol. 49, 579-584 (1972). VANDE WALLE, 1., and OLSSON, R.: The y-aminobutyric acid shunt in germinating Sinapsis alba seeds. Plant Sci. Lett. 31, 269-273 (1983).
Received April 18, 1985; accepted May 13, 1985 Author's address: L. GALLES CHI, Dipartimento di Scienze Botaniche, Universita di Pisa, Pisa, Ita.Iia.
Biochem. Physiol. Pflanzen 180, 633 - 635 (1985)
Buchbesprechungen MENGEL, KONRAD: Ernahrung und Stoffwechsel der Pflanz e. 6. iiberarb. Auflage. 431 Seiten, 158 Abbildungen, 16 teils farbi ge Tafeln, 97 Tabellen. VEB Gustav Fischer Verlag, Jena 1984. Preis : L einen DDR 34,00 M; Ausland 39,00 Dl'IL Auch die vorliegende 6. Auflage des " Mengel" behalt die bisherige Dreiteilung des Stoffgebietes bei, namlich in 1. Biochemic wichtiger Stoffwechselvorgange, 2. Erniihrungs- und Ertragsphysiologie und 3. Spezielle Wirkung und Bedeutung der einzelnen Pflanzennahrstoffe. Der 1. Teil behandelt zunachst chemische Bindung, Sorption und enzymatische Reaktionen, urn danach auf dieser Grundlage Energie- und Kohlenhydratstoffwechsel, Lipidstoffwechsel sowie den Stoffwechsel der NVcrbindungen zu bcschreiben. Er wurde gegeniiber der 5. Auflage am stiirksten iiberarbeitet. Dies betrifft nicht nur die Anwendung der IUPAC-Nomenklatur, sondern auch die Einordnung bestimmt er, in der vorigen Auflage selbst andig ausgewiesener Teilgebiete. So wird die Abrufung der genetischen Information beim N-Stoffwechscl besprochen, wahrend der Feinbau der Zelle sowie die Phytohormone und Wirkstoffe jetzt im Teil 2 (Ernahrungs- und Ertragsphysiologie) erscheinen. 1m 2. Tail widmet sich der Autor zunachst der Charakterisierung der Pflanzennahrstoffe, dem Boden als Nahrmedium der hiiheren Pflanze und der Stoffaufnahme bzw. dem Stofftransport. Es foJ gen Abschnitte iiber Wuchsstoffe, Wachstumsregulatoren und Biozide sowie iiber die Beziehungen zwischen Erniihrung bzw. Diingung einerseits und Ertragsbildung bzw. Qualitat pflanzlicher Produkte andererseits. Neu aufgenommen wurden Teilabschnitte iib er Wurzelwachstum und -morphologie, Rhizosphare und Mykorrhiza sowie Nitrifikationsinhibitoren. Der 3. Teil befaBt sich mit den fiir Pflanzen bedeutsamen chemischen Elementen. Es werden im einzelnen Vorkommen, Kreislauf in der Natur (soweit Kenntnisse vorhanden), Aufnahme und Vert eilung bei Pflanzen sowie Fragen der Ernahrung und Diingung besprochen. Der Verfasser nimmt