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Gummosis in tulips under the influence of ethephon
Scientia Horticulturae, 40 (1989) 153-162
153
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Gummosis in Tulips Under the Influence of Ethephon W.J. DE MUNK ~and M. SANIEWSKI~
~Bulb Research Centre, Lisse (The Netherlands) "-Research Institute of Pomology and Floriculture, Skierniewice (Poland) (Accepted for publication 26 December 1988)
ABSTRACT De Munk, W.J. and Saniewski, M., 1989. Gummosis in tulips under the influence of ethephon. Scientia Hortic., 40: 153-162. The formation of gums and gum-like substances in bulb scales, stem tissue and perianth leaves of tulip cultivars 'Apeldoorn' and 'Oxford' was found to occur after the application of lanolin paste containing 1 or 5% 2-chloroethylphosphonic acid (ethephon), 0.2% indole-3-acetic acid (IAA) or both ethephon and IAA. The composition of the gums induced by ethephon in 'Apeldoorn' bulbs was analysed after hydrolysis. Xylose and arabinose were mainly found with traces of glucose, mannose and uronic acid. Keywords: auxin; carbohydrates; ethephon; gum; tulips. Abbreviations: ethephon = 2-chloroethylphosphonic acid; IAA = indole-3-acetic acid.
INTRODUCTION
The formation of gums in tulip bulbs is a well-known disorder that can be induced by ethylene (Kamerbeek et al., 1971; Kamerbeek and De Munk, 1976; Bergman et al., 1983). Ethylene concentrations as low as 0.05 ltl l-1 are effective, and wounding or mechanical damage of the bulb tissue promotes the extrusion of the substance. Also ethephon, applied to bulbs as a source of ethylene, can cause gummosis and other disorders in tulips similar to ethylene disorders (Anonymous, 1972; Moe and Hagness, 1975; Moe, 1980; De Hertogh et al., 1980 ). It is also known that tulip bulbs infected by the fungus Fusariurn oxysporum f. tulipae can produce considerable quantities of ethylene, enough to cause gummosis in diseased and healthy bulbs stored in the same storage room (De Munk, 1972; Swart and Kamerbeek, 1976, 1977). Gums are mainly found inside the outer bulb scale some cell layers below the
0304-4238/89/$03.50
© 1989 Elsevier Science Publishers B.V.
154 epidermis, but in certain cultivars they will also occur in the basal plate, from which they can be extruded into the central core of the bulb. This paper describes some special forms of gum formation in the stem and the flower bud, which occur after the administration of plant growth regulators in lanolin paste on different organs. Furthermore, the composition of the gums from bulb scales has been analysed. MATERIALS AND METHODS E x p e r i m e n t s on g u m p r o d u c t i o n a n d a n a l y s i s M a t e r i a l . - Tulip bulbs of cultivar 'Apeldoorn' (12-cm circumference) were
derived from a commercial stock at the end of June and stored at 18-22 ° C. G u m p r o d u c t i o n . - For the production of gums the dry tunics were removed from the bulbs and a lanolin paste containing 5% ethephon ( w / w ) was applied at the basal side of the scales. Treated bulbs were kept at a temperature of 1822°C. A n a l y s i s . - Gums from ethephon-treated 'Apeldoorn' bulbs were collected by
hand and hydrolysed in I N H2SO4in glass vials in boiling water for 8 h. Subsequently the solution was neutralized with Ba (CO~)2. For the separation of free sugars, descending paper chromatography was used. Chromatograms were developed for 30-40 h in the upper phase of the following solvent: ethyl acetate - acetic acid - water ( 3 : 1 : 3 v / v / v ) . Sugars were detected by spraying the chromatograms with anisidine phthalate (0.1 M solution of p-anisidine and 0.1 M phthalamic acid in 96% ethanol) and a few minutes heating at 90 ° C. E x p e r i m e n t s with growth regulation Material. - Tulip plants were raised from bulbs ( 12-cm circumference ) of com-
mercial stocks of 'Apeldoorn' after precooling for 12 weeks at 5 ° C, and of cultivar 'Oxford' after storage in planted condition for 12 months at - 2 °C ('ice tulips'). The plants were forced at 17 °C under artificial lighting by fluorescent tubes Philips T L 44 for 12 h day -1 (5.3 W m -2 or 17.7 mol s - l m - 2 ) . T r e a t m e n t s . - The experiments involved the excision of the leaves (defoliation), the flower bud (decapitation) or the shoot below the basal leaf, when the stems reached a length of 10-20 cm. After the excision a lanolin paste was applied containing 1 or 5% ethephon (w/w), 0.2% IAA ( w / w ) or both ethephon and IAA. The paste was applied to the cut surface of the stem, or to intact plants ringlike to the stem just under the flower bud (see also Saniewski and De Munk, 1981 ).
155 Morphological observations were conducted during the development of the plants after the experimental treatments; lengths of stem internodes were measured when the stems had reached their maximal length. Length determinations were statistically evaluated by analysis of variance and the KruskalWallis test (Kruskal and Wallis, 1952). RESULTS The application of lanolin paste containing 5% ethephon around the basal plate of 'Apeldoorn' bulbs at the beginning of July, caused strong gummosis. Large bursting blisters were formed and gums were excreted (Fig. 1). In the case of small blisters, gums were found inside the tissue of outer bulb scales about 5 cell layers below the epidermis; the cell layers abaxial of the gum blister did not contain starch granules, in contrast to the parenchyma cells at the other side (Fig. 2). Chromatographic analysis showed that samples of hydrolysed gums contained mainly xylose and arabinose; only traces of glucose, mannose and uronic acid were found (Fig. 3). The application of lanolin paste containing 5% ethephon to intact plants around the stem, just below the flower bud, resulted in the formation of gum blisters at the basal end of the perianth leaves (Fig. 4). The outflow of gums and hardening of the substance, earlier described by Bergman et al. ( 1983 ) for bulb-scale tissue, was achieved when the perianth base was wounded with a needle. Also in the absence of blisters this outflow occurred after wounding.
Fig. 1. Extrudedgum on the outer scalesofbulbs 'Apeldoorn'treated with lanolinpaste containing 5% ethephon on 7 July; photographedon 30 July.
156
Fig. 2. Cross section through a tulip bulb scale showing ruptured tissue forming a lumen filled with gum. The cells around and the cell layers abaxial of the gum blister do not contain starch granules in contrast to the internal parenchyma cells. EP = epidermis, L = lumen with gum.
O
g •
S
e
U
e
e
s
Fig. 3. Paper chromatogram of free sugars obtained after hydrolysis for 8 h in 1 N + H2SO4 at 100°C of ethephon-induced gum (see Fig. 1 ). s=standard sugars; e=sample of hydrolysed gum in different amounts; x--- xylose; a=arabinose; g=glucose; m=mannose; u--uronic acid. (Identification of x, g and u on account of data from other chromatograms not shown in this paper.) Application of lanolin paste containing 1 or 5% ethephon on the cut surface of the stem after excision of the shoot below the basal leaf resulted in the extrusion of a gumlike substance from the wounded area within 4 days (Fig. 5). In cases where spontaneous extrusion was not obvious, a small transverse
157
Fig. 4. Flower bud of 'Oxford'tulip showinggum formation after the application of lanolin paste containing5% ethephon around the stemjust belowthe flowerbud. Blisters at the site of perianth insertion filledwith gum.
Fig. 5. Gum formation at the cut surface of the basal internode after excision of the shoot of 'Apeldoorn'tulips and the applicationof lanolin paste containing 1% ethephon. incision in the stem tissue led to the appearance of the gum-like substance (Fig. 6) Simultaneous administration of 0.2% IAA and 5% ethephon at the top of the stem after defoliation and decapitation resulted in the extrusion of a viscous gum-like substance from the leaf axils. The extrusion was maximal at the upper node (Fig. 7). This phenomenon was not observed when IAA or ethephon was applied alone. The latter kind of gummosis coincided with an effect on stem growth by IAA and ethephon (Table 1 ). IAA restored the elongation growth of the stem after
158
Fig. 6. Excised basal internodes of 'Oxford' tulips showing the extrusion of gum from a transverse incision in the tissue after excision of the shoot and the application of plain lanolin (upper segment) or lanolin paste containing 5 % ethephon (lower segment). The incision was made 4 days after the application of the lanolin. Basal end at the left side.
Fig. 7. Extrusion of a viscous gum-like substance from the leaf axil of an 'Apeldoorn' tulip after the application of lanolin paste containing 5% ethephon and 0.2% IAA to the cut surface of the decapitated and defoliated stem.
159 TABLE 1 Elongation growth of the stem internodes of tulip 'Apeidoorn', precooled at 5°C, after decapitation, defoliation and the application of plain lanolin or lanolin paste containing IAA, ethephon or both substances to the cut surface of the stem Treatment
Untreated intact plants Flower bud and leaves removed Plain lanolin 0.2% IAA 5% ethephon
0.2% IAA+5% ethephon
Final length of internodes ~ (cm) 1st (basal)
2nd
3rd
4th
Total stem length
9.8 ~
7.0b
7.3 ¢
28.8 ¢
52.9 ~
10.6a 10.2~ 10.9~
3.9~ 5.6 a 5.0 a
1.8a 5.7c 2.4a
2.2~ 25.1 c 2.7~
18.5 b 46.6 c 21.0 h
10.7a
4.7a
3.8 b
18.7b
37.9 d
Other morphological symptoms
Beginning of flowering 16 December
Loss of turgor in stem tissue, yellowing of top internode Exudation of brown viscous sap from top internode and the axils of the leaves
1The lengths of the internodes at the moment of application of lanolin paste were: first (basal) internode 6-11 cm; second internode 2-4 cm; third internode 1-2 cm; top internode 1-2 cm. Means in the same column followed by the same superscript do not differ at the 5% level of significance.
Fig. 8. Splitting and outward curling of stem segments of basal internodes of 'Apeldoorn' tulips after excision of the shoots and the application of from left to right: plain lanolin paste; lanolin paste containing 5% ethephon; 0.2% IAA; 5% e t h e p h o n + 0.2% IAA.
160
decapitation and defoliation, while simultaneous administration of 0.2% IAA and 5% ethephon led to suppression of the IAA-stimulated elongation growth. In this respect, the upper internode was most reactive; the elongation growth of the basal internode was not significantly affected, because the elongation was almost complete at the time of the experiment. Finally, splitting and outward curling of stem tissue of 'Apeldoorn' tulips was observed after excision of the shoot below the basal leaf. This curling effect was strengthened or abolished, after administration on the cut surface of lanolin paste with 5% ethephon or 0.2% IAA, respectively. After simultaneous administration of 0.2% IAA and 5% ethephon curling was not observed (Fig. 8). This might be an indication that curling symptoms that occur without administration of ethephon are caused by endogenous ethylene released after wounding. DISCUSSION
The chemical composition of gums in stone-fruit trees and their fruits has been widely analysed (Boothby, 1983). Some authors have noted that gum formation is accompanied by the disappearance of starch grains, suggesting that gum originates from starch (Boothby, 1983; Gedalovich and Fahn, 1985 ). Nair et al. (1980) suggest that degradation products of starch grains and cell walls contribute to gum production in the bark of Azadirachta indica. The coincidental disappearance of starch, that we observed during the formation of gums in tulip bulbs, is in accordance with these suggestions. The appearance of the pentose sugars xylose and arabinose and traces of glucose, mannose and uronic acid after hydrolysis of gums induced by ethephon in tulip bulbs, might be a further indication that the carbohydrate metabolism is strongly involved in the production of gums. It is well known that in scales of tulip bulbs, starch and fructosans are the main storage carbohydrates (Algera, 1947; Aung et al., 1973; Moe and Wickstrom, 1973; Haaland and Wickstrom, 1975) and it is possible that fructosans and cell-wall material, especially from the middle lamellae, participate in gum formation. This requires further study. We found that a high percentage of ethephon inhibited internode elongation induced by IAA, when these substances were applied together (Table 1 ). Gilford and Rees ( 1973 ) showed that elongation is almost entirely caused by elongation of cells produced in an earlier phase of the development. This means that ethephon exerts its influence upon cell elongation induced by exogenously applied auxin. Ethephon applied below the flower bud in intact plants, in higher concentrations, caused flower-bud blasting. Consequently, auxin production by and transportation from the gynoecium will ultimately stop. On the other hand, it is known that ethylene inhibits basipetal transport of auxin in many plants or their organs (Abeles, 1973 ). So the inhibitory effect of ethephon on stem elongation can be explained by decreasing concentrations of endogenous auxin in
161
the stem tissue. However, a direct inhibitory effect of ethephon on cell elongation in the presence of auxin cannot be excluded. It cannot be said in what way ethephon exerts its influence in our experiments. It is particularly interesting that ethephon induced gummosis not only in bulb scales but also in the base of the perianth and in stem tissue. The ability of the various tissues of the plant to produce gums points to a general feature of gum formation, although it cannot yet be said that the composition of all gums is similar. From tissue-culture work it is known that high concentrations of auxins in the medium reduce the uptake of sugars by cells from that medium, while low auxin concentrations enhance starch accumulation in suspension cultures and reduce cell division (P.C.G. van der Linde, personal communication, 1988). We found that both auxin and ethephon have an effect on the development of the shoot. Interaction between auxin and ethylene is a wellknown phenomenon (Abeles, 1973). The administration of ethephon, inhibiting the growth and development of the shoot might result in a reduced uptake of carbohydrates, while the remobilization of storage carbohydrates continues or will even be enhanced. In that case gummosis is a process to redress a balanced condition within the tissues in terms of sinks and sources. ACKNOWLEDGEMENT
We wish to thank Dr. B.H.H. Bergman for preparing and photographing a cross section of a gum blister in the bulb scale of a tulip.
REFERENCES Abeles, R.B., 1973. Ethylene in Plant Biology. Academic Press, New York, NY, 302 pp. Algera, L., 1947. Over den invloed van de temperatuur op de koolhydraat-stofwisseling en ademhaling bij de tulp en de hyacinth en de beteekenis daarvan voor de ontwikkeling der plant. Meded. Landbouwhogesch. Wageningen, 48: 85-183. Anonymous, 1972. To determine the effects of ethephon, a chemical growth regulator, on the growth and flowering of tulip. Kirton Experimental Horticulture Station, Ninth Report, Part I. Bulbs, pp. 76-82. Aung, L.H., Tognoni, F. and De Hertogh, A.A., 1973. Changes in the carbohydrates of tulip bulbs during development. HortScience, 8: 207-208. Bergman, B.H.H., Eijkman, A.J., Muller, P.J., Slogteren, D.H.M. van and Weststeijn, G., 1983. Ziekten en afwijkingen bij bolgewassen. Deel I, Liliaceae. Laboratorium voor Bloembollenonderzoek, Lisse, 181 pp. Boothby, D., 1983. Gummosis of stone-fruit trees and their fruits. J. Sci. Food Agric., 34: 1-7. De Hertogh, A.A., Dilley, D.R. and Blakely, N., 1980. Response variation of tulip cultivars to exogenous ethylene. Acta Hortic., 109: 205-210. De Munk, W.J., 1972. Bud necrosis, a storage disease of tulips, III. The influence of ethylene and mites. Neth. J. Plant. Pathol., 78: 168-178. Gedalovich, E. and Fahn, A., 1985. Ethylene and gum duct formation in citrus. Ann. Bot., 56:571577.
162 Gilford, J.Mc.D. and Rees, A.R., 1973. Growth of the tulip shoot. Scientia Hortic., 1: 143-156. Haaland, E. and Wickstrom, A., 1975. The effect of storage temperature on carbohydrate interconversion in tulip bulbs. Acta Hortic., 47: 371-376. Kamerbeek, G.A. and De Munk, W.J., 1976. A review of ethylene effects in bulbous plants. Scientia Hortic., 4: 101-115. Kamerbeek, G.A., Verlind, A.L. and Schipper, J.A., 1971. Gummosis of tulip bulbs caused by ethylene. Acta Hortic., 23: 167-172. Kruskal, W.H. and Wallis, W.A., 1952. Use of ranks in one-criterion variance analysis. J. Am. Stat. Assoc., 47: 584-618. Moe, R., 1980. The use of ethephon for control of plant height in daffodils and tulips. Acta Hortic., 109: 197-204. Moe, R. and Hagness, A.K., 1975. The influence of storage temperature and 2-chloroethylphosphonic acid (ethephon) on shoot elongation and flowering in tulips. Acta Hortic., 47: 307-318. Moe, R. and Wickstr~m, A., 1973. The effect of storage temperature in shoot growth, flowering and carbohydrate metabolism in tulip bulbs. Physiol. Plant., 28: 81-87. Nair, M.N.B., Patel, K.R., Shah, J.J. and Pandalai, R.C., 1980. Effect of ethephon (2-chloroethylphosphonic acid) on gummosis in the bark of Azadirachta indica. Indian J. Exp. Bot., 18: 500-503. Saniewski, M. and De Munk, W.J., 1981. Hormonal control of shoot elongation in tulips. Scientia Hortic., 15: 363-372. Swart, A. and Kamerbeek, G.A., 1976. Different ethylene production in vitro by several species and formae speciales of Fusarium. Neth. J. Plant Pathol., 82: 81-84. Swart, A. and Kamerbeek, G.A., 1977. Ethylene production and mycelium growth of the tulip strain of Fusarium oxysporum as influenced by shaking of and oxygen supply to the culture medium. Physiol. Plant., 39: 38-44.
153
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Gummosis in Tulips Under the Influence of Ethephon W.J. DE MUNK ~and M. SANIEWSKI~
~Bulb Research Centre, Lisse (The Netherlands) "-Research Institute of Pomology and Floriculture, Skierniewice (Poland) (Accepted for publication 26 December 1988)
ABSTRACT De Munk, W.J. and Saniewski, M., 1989. Gummosis in tulips under the influence of ethephon. Scientia Hortic., 40: 153-162. The formation of gums and gum-like substances in bulb scales, stem tissue and perianth leaves of tulip cultivars 'Apeldoorn' and 'Oxford' was found to occur after the application of lanolin paste containing 1 or 5% 2-chloroethylphosphonic acid (ethephon), 0.2% indole-3-acetic acid (IAA) or both ethephon and IAA. The composition of the gums induced by ethephon in 'Apeldoorn' bulbs was analysed after hydrolysis. Xylose and arabinose were mainly found with traces of glucose, mannose and uronic acid. Keywords: auxin; carbohydrates; ethephon; gum; tulips. Abbreviations: ethephon = 2-chloroethylphosphonic acid; IAA = indole-3-acetic acid.
INTRODUCTION
The formation of gums in tulip bulbs is a well-known disorder that can be induced by ethylene (Kamerbeek et al., 1971; Kamerbeek and De Munk, 1976; Bergman et al., 1983). Ethylene concentrations as low as 0.05 ltl l-1 are effective, and wounding or mechanical damage of the bulb tissue promotes the extrusion of the substance. Also ethephon, applied to bulbs as a source of ethylene, can cause gummosis and other disorders in tulips similar to ethylene disorders (Anonymous, 1972; Moe and Hagness, 1975; Moe, 1980; De Hertogh et al., 1980 ). It is also known that tulip bulbs infected by the fungus Fusariurn oxysporum f. tulipae can produce considerable quantities of ethylene, enough to cause gummosis in diseased and healthy bulbs stored in the same storage room (De Munk, 1972; Swart and Kamerbeek, 1976, 1977). Gums are mainly found inside the outer bulb scale some cell layers below the
0304-4238/89/$03.50
© 1989 Elsevier Science Publishers B.V.
154 epidermis, but in certain cultivars they will also occur in the basal plate, from which they can be extruded into the central core of the bulb. This paper describes some special forms of gum formation in the stem and the flower bud, which occur after the administration of plant growth regulators in lanolin paste on different organs. Furthermore, the composition of the gums from bulb scales has been analysed. MATERIALS AND METHODS E x p e r i m e n t s on g u m p r o d u c t i o n a n d a n a l y s i s M a t e r i a l . - Tulip bulbs of cultivar 'Apeldoorn' (12-cm circumference) were
derived from a commercial stock at the end of June and stored at 18-22 ° C. G u m p r o d u c t i o n . - For the production of gums the dry tunics were removed from the bulbs and a lanolin paste containing 5% ethephon ( w / w ) was applied at the basal side of the scales. Treated bulbs were kept at a temperature of 1822°C. A n a l y s i s . - Gums from ethephon-treated 'Apeldoorn' bulbs were collected by
hand and hydrolysed in I N H2SO4in glass vials in boiling water for 8 h. Subsequently the solution was neutralized with Ba (CO~)2. For the separation of free sugars, descending paper chromatography was used. Chromatograms were developed for 30-40 h in the upper phase of the following solvent: ethyl acetate - acetic acid - water ( 3 : 1 : 3 v / v / v ) . Sugars were detected by spraying the chromatograms with anisidine phthalate (0.1 M solution of p-anisidine and 0.1 M phthalamic acid in 96% ethanol) and a few minutes heating at 90 ° C. E x p e r i m e n t s with growth regulation Material. - Tulip plants were raised from bulbs ( 12-cm circumference ) of com-
mercial stocks of 'Apeldoorn' after precooling for 12 weeks at 5 ° C, and of cultivar 'Oxford' after storage in planted condition for 12 months at - 2 °C ('ice tulips'). The plants were forced at 17 °C under artificial lighting by fluorescent tubes Philips T L 44 for 12 h day -1 (5.3 W m -2 or 17.7 mol s - l m - 2 ) . T r e a t m e n t s . - The experiments involved the excision of the leaves (defoliation), the flower bud (decapitation) or the shoot below the basal leaf, when the stems reached a length of 10-20 cm. After the excision a lanolin paste was applied containing 1 or 5% ethephon (w/w), 0.2% IAA ( w / w ) or both ethephon and IAA. The paste was applied to the cut surface of the stem, or to intact plants ringlike to the stem just under the flower bud (see also Saniewski and De Munk, 1981 ).
155 Morphological observations were conducted during the development of the plants after the experimental treatments; lengths of stem internodes were measured when the stems had reached their maximal length. Length determinations were statistically evaluated by analysis of variance and the KruskalWallis test (Kruskal and Wallis, 1952). RESULTS The application of lanolin paste containing 5% ethephon around the basal plate of 'Apeldoorn' bulbs at the beginning of July, caused strong gummosis. Large bursting blisters were formed and gums were excreted (Fig. 1). In the case of small blisters, gums were found inside the tissue of outer bulb scales about 5 cell layers below the epidermis; the cell layers abaxial of the gum blister did not contain starch granules, in contrast to the parenchyma cells at the other side (Fig. 2). Chromatographic analysis showed that samples of hydrolysed gums contained mainly xylose and arabinose; only traces of glucose, mannose and uronic acid were found (Fig. 3). The application of lanolin paste containing 5% ethephon to intact plants around the stem, just below the flower bud, resulted in the formation of gum blisters at the basal end of the perianth leaves (Fig. 4). The outflow of gums and hardening of the substance, earlier described by Bergman et al. ( 1983 ) for bulb-scale tissue, was achieved when the perianth base was wounded with a needle. Also in the absence of blisters this outflow occurred after wounding.
Fig. 1. Extrudedgum on the outer scalesofbulbs 'Apeldoorn'treated with lanolinpaste containing 5% ethephon on 7 July; photographedon 30 July.
156
Fig. 2. Cross section through a tulip bulb scale showing ruptured tissue forming a lumen filled with gum. The cells around and the cell layers abaxial of the gum blister do not contain starch granules in contrast to the internal parenchyma cells. EP = epidermis, L = lumen with gum.
O
g •
S
e
U
e
e
s
Fig. 3. Paper chromatogram of free sugars obtained after hydrolysis for 8 h in 1 N + H2SO4 at 100°C of ethephon-induced gum (see Fig. 1 ). s=standard sugars; e=sample of hydrolysed gum in different amounts; x--- xylose; a=arabinose; g=glucose; m=mannose; u--uronic acid. (Identification of x, g and u on account of data from other chromatograms not shown in this paper.) Application of lanolin paste containing 1 or 5% ethephon on the cut surface of the stem after excision of the shoot below the basal leaf resulted in the extrusion of a gumlike substance from the wounded area within 4 days (Fig. 5). In cases where spontaneous extrusion was not obvious, a small transverse
157
Fig. 4. Flower bud of 'Oxford'tulip showinggum formation after the application of lanolin paste containing5% ethephon around the stemjust belowthe flowerbud. Blisters at the site of perianth insertion filledwith gum.
Fig. 5. Gum formation at the cut surface of the basal internode after excision of the shoot of 'Apeldoorn'tulips and the applicationof lanolin paste containing 1% ethephon. incision in the stem tissue led to the appearance of the gum-like substance (Fig. 6) Simultaneous administration of 0.2% IAA and 5% ethephon at the top of the stem after defoliation and decapitation resulted in the extrusion of a viscous gum-like substance from the leaf axils. The extrusion was maximal at the upper node (Fig. 7). This phenomenon was not observed when IAA or ethephon was applied alone. The latter kind of gummosis coincided with an effect on stem growth by IAA and ethephon (Table 1 ). IAA restored the elongation growth of the stem after
158
Fig. 6. Excised basal internodes of 'Oxford' tulips showing the extrusion of gum from a transverse incision in the tissue after excision of the shoot and the application of plain lanolin (upper segment) or lanolin paste containing 5 % ethephon (lower segment). The incision was made 4 days after the application of the lanolin. Basal end at the left side.
Fig. 7. Extrusion of a viscous gum-like substance from the leaf axil of an 'Apeldoorn' tulip after the application of lanolin paste containing 5% ethephon and 0.2% IAA to the cut surface of the decapitated and defoliated stem.
159 TABLE 1 Elongation growth of the stem internodes of tulip 'Apeidoorn', precooled at 5°C, after decapitation, defoliation and the application of plain lanolin or lanolin paste containing IAA, ethephon or both substances to the cut surface of the stem Treatment
Untreated intact plants Flower bud and leaves removed Plain lanolin 0.2% IAA 5% ethephon
0.2% IAA+5% ethephon
Final length of internodes ~ (cm) 1st (basal)
2nd
3rd
4th
Total stem length
9.8 ~
7.0b
7.3 ¢
28.8 ¢
52.9 ~
10.6a 10.2~ 10.9~
3.9~ 5.6 a 5.0 a
1.8a 5.7c 2.4a
2.2~ 25.1 c 2.7~
18.5 b 46.6 c 21.0 h
10.7a
4.7a
3.8 b
18.7b
37.9 d
Other morphological symptoms
Beginning of flowering 16 December
Loss of turgor in stem tissue, yellowing of top internode Exudation of brown viscous sap from top internode and the axils of the leaves
1The lengths of the internodes at the moment of application of lanolin paste were: first (basal) internode 6-11 cm; second internode 2-4 cm; third internode 1-2 cm; top internode 1-2 cm. Means in the same column followed by the same superscript do not differ at the 5% level of significance.
Fig. 8. Splitting and outward curling of stem segments of basal internodes of 'Apeldoorn' tulips after excision of the shoots and the application of from left to right: plain lanolin paste; lanolin paste containing 5% ethephon; 0.2% IAA; 5% e t h e p h o n + 0.2% IAA.
160
decapitation and defoliation, while simultaneous administration of 0.2% IAA and 5% ethephon led to suppression of the IAA-stimulated elongation growth. In this respect, the upper internode was most reactive; the elongation growth of the basal internode was not significantly affected, because the elongation was almost complete at the time of the experiment. Finally, splitting and outward curling of stem tissue of 'Apeldoorn' tulips was observed after excision of the shoot below the basal leaf. This curling effect was strengthened or abolished, after administration on the cut surface of lanolin paste with 5% ethephon or 0.2% IAA, respectively. After simultaneous administration of 0.2% IAA and 5% ethephon curling was not observed (Fig. 8). This might be an indication that curling symptoms that occur without administration of ethephon are caused by endogenous ethylene released after wounding. DISCUSSION
The chemical composition of gums in stone-fruit trees and their fruits has been widely analysed (Boothby, 1983). Some authors have noted that gum formation is accompanied by the disappearance of starch grains, suggesting that gum originates from starch (Boothby, 1983; Gedalovich and Fahn, 1985 ). Nair et al. (1980) suggest that degradation products of starch grains and cell walls contribute to gum production in the bark of Azadirachta indica. The coincidental disappearance of starch, that we observed during the formation of gums in tulip bulbs, is in accordance with these suggestions. The appearance of the pentose sugars xylose and arabinose and traces of glucose, mannose and uronic acid after hydrolysis of gums induced by ethephon in tulip bulbs, might be a further indication that the carbohydrate metabolism is strongly involved in the production of gums. It is well known that in scales of tulip bulbs, starch and fructosans are the main storage carbohydrates (Algera, 1947; Aung et al., 1973; Moe and Wickstrom, 1973; Haaland and Wickstrom, 1975) and it is possible that fructosans and cell-wall material, especially from the middle lamellae, participate in gum formation. This requires further study. We found that a high percentage of ethephon inhibited internode elongation induced by IAA, when these substances were applied together (Table 1 ). Gilford and Rees ( 1973 ) showed that elongation is almost entirely caused by elongation of cells produced in an earlier phase of the development. This means that ethephon exerts its influence upon cell elongation induced by exogenously applied auxin. Ethephon applied below the flower bud in intact plants, in higher concentrations, caused flower-bud blasting. Consequently, auxin production by and transportation from the gynoecium will ultimately stop. On the other hand, it is known that ethylene inhibits basipetal transport of auxin in many plants or their organs (Abeles, 1973 ). So the inhibitory effect of ethephon on stem elongation can be explained by decreasing concentrations of endogenous auxin in
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the stem tissue. However, a direct inhibitory effect of ethephon on cell elongation in the presence of auxin cannot be excluded. It cannot be said in what way ethephon exerts its influence in our experiments. It is particularly interesting that ethephon induced gummosis not only in bulb scales but also in the base of the perianth and in stem tissue. The ability of the various tissues of the plant to produce gums points to a general feature of gum formation, although it cannot yet be said that the composition of all gums is similar. From tissue-culture work it is known that high concentrations of auxins in the medium reduce the uptake of sugars by cells from that medium, while low auxin concentrations enhance starch accumulation in suspension cultures and reduce cell division (P.C.G. van der Linde, personal communication, 1988). We found that both auxin and ethephon have an effect on the development of the shoot. Interaction between auxin and ethylene is a wellknown phenomenon (Abeles, 1973). The administration of ethephon, inhibiting the growth and development of the shoot might result in a reduced uptake of carbohydrates, while the remobilization of storage carbohydrates continues or will even be enhanced. In that case gummosis is a process to redress a balanced condition within the tissues in terms of sinks and sources. ACKNOWLEDGEMENT
We wish to thank Dr. B.H.H. Bergman for preparing and photographing a cross section of a gum blister in the bulb scale of a tulip.
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