Control by Ethylene of Arginine Decarboxylase Activity in Pea Seedlings and Its Implication for Hormonal Regulation of Plant Growth

Abstract

Activity of arginine decarboxylase in etiolated pea seedlings appears 24 hours after seed imbibition, reaches its highest level on the 4th day, and levels off until the 7th day. This activity was found in the apical and subapical tissue of the roots and shoots where intensive DNA synthesis occurs. Exposure of the seedlings to ethylene greatly reduced the specific activity of this enzyme. The inhibition was observed within 30 min of the hormone application, and maximal effect-90% inhibition-after 18 hours. Ethylene at physiological concentrations affected the enzyme activity; 50% inhibitory rate was recorded at 0.12 microliters per liter ethylene and maximal response at 1.2 microliters per liter. Ethylene provoked a 5-fold increase in the K,," of arginine decarboxylase for its substrate and reduced the V.w by 10-fold. However, the enzyme recovered from the inhibition and regained control activity 7 hours after transferral of the seedlings to ethylene-free atmosphere. Reducing the endogenous level of ethylene in the tissue by hypobaric pressure, or by exposure to light, as well as interfering with ethylene action by treatment with silver thiosulfate or 2,5-norbornadiene, caused a gradual increase in the specific activity of arginine decarboxylase in the apical tissue of the etiolated seedlings. On the basis of these findings, the possible control of arginine decarboxylase activity by endogenous ethylene, and its implication for the hormone effect on plant growth, are discussed.arises from the study of Bagni (5), who first reported that growth ofdormant Helianthus tuberosus was initiated when either auxin or one of the polyamines was added to the medium and that growth was accompanied by an increase in polyamine titer. There are now recorded instances of increased polyamine biosynthesis and titer in plants following application of each of the growthpromoting plant hormones: auxin (6), GA3 (13), and cytokinin (28). On the other hand, retardation ofgrowth by ABA has been shown to be accompanied by decreased polyamine biosynthesis (28). Consequently, the role of 'second messenger' mediating the effect of plant hormones has been proposed for polyamines (14).Ethylene has been shown to inhibit cell division, DNA synthesis, and growth in meristems of roots, shoots, and axillary buds of etiolated pea seedlings (1). In the shoot apex, cell division was almost completely annulled by ethylene and only 60% inhibition was observed in the root apex (1). The gas inhibits cell division by blocking a stage before prophase (1). In the subapical regions of the seedling, the hormone inhibited cell expansion and DNA synthesis (2). In the various parts of the seedling, a qualitative relationship was found between the inhibition of DNA synthesis, cell division, and growth caused by ethylene (1).In view of the above, a study was undertaken to pursue a possible involvement of polyamines in the effects of ethylene on plant growth. In this communication, we show that ethylene provokes a pronounced and reversible inhibition of ADC2 ac...

Ethylene-Induced Polyamine Accumulation in Rice (Oryza sativa L.) Coleoptiles

“…These findings contrast with the results from the deepwater rice system (3), where significant accumulation of spermidine was observed in response to ethylene, but putrescine showed only a relatively small increase. The observation that in etiolated pea seedlings polyamine biosynthesis is inhibited by ethylene shows even more of a contrast (1). Moreover, ethylene inhibits growth in pea, whereas it promotes growth in both types of rice.…”

“…In the experiment under sealed conditions, 10 seedlings were transferred into a 30-mL flask with 2 mL of 10' M Mes buffer solution (pH 5.5), and the flasks were sealed with silicone rubber caps. Ethylene treatment was administered by injecting 3 mL of 10 gL/L ethylene into the sealed containers to make a concentration of 1 Figure 2. In aerobic controls, putrescine concentra- tion increased gradually within the initial 2 d of treatment and decreased subsequently ( Fig.…”

“…Stresses such as oxygen deficiency (19-21), chilling (11), high saline, low pH, and K+ and Mg2+ deficiency (5,8,9) increase polyamine contents and their biosynthetic enzyme activities (5,8,9). Ethylene was also found to influence polyamine biosynthesis (1,3,6,12,13,22,24); however, whether the effect was inhibition or stimulation depended on the plant system (5). In 3 Abbreviations: ADC, arginine decarboxylase; ACC, 1-aminocyclopropane-1-carboxylic acid; DFMA, a-difluromethylarginine; DFMO, a-difluromethylornithine; MeOH, methanol; ODC, omithine decarboxylase; PMSF, phenylmethylsulfonylfluride; SAM, S-adenosylmethionine; SAMDC, S-adenosylmethionine decarboxylase; PCA, perchloric acid.…”

Polyamine Levels and Tomato Fruit Development: Possible Interaction with Ethylene

“…Free polyamines inhibited ethylene production in a variety of tissues (2,5,8,24) opposite effects in relation to fruit ripening and senescence (3,5,9,22,26). Because of this, polyamine and ethylene physiologies may be linked during fruit development.…”

Hormonal regulation of S-adenosylmethionine synthase transcripts in pea ovaries

“…Polyamines and ethylene biosynthetic pathways are competitive: when specific inhibitors are used to prevent either ethylene or spermidine biosynthesis, the flow of carbon atoms from SAM through the alternative pathway is favoured [20,39]. Still, exogenously applied polyamines inhibit the plant's ability to produce ethylene [1] and, conversely, exogenous ethylene suppresses the accumulation of polyamines [2]. It has been shown that polyamines have the potential to regulate ethylene biosynthesis by affecting the accumulation of ACC synthase transcripts [19].…”