Ethylene production abscisic acid

When subjected to drought stress, excised wheat Triticum aestivum L.) leaves increase ethylene production as a result of an increased synthesis of ACC 71 and an increased activity of the ethylene-forming enzyme (EFE) which catalyzes the conversion of ACC 71 to ethylene. Rehydratation to relieve water stress reduces EFE activity to levels similar to those in non-stressed tissue. Pretreatment of the leaves with N-benzyladenine (BA) 75 or indole-3-acetic acid lAA 76 prior to drought stress caused further increase in ethylene production. Conversely, pretreatment of wheat leaves with abscisic acid ABA 77 reduced ethylene production to levels of non-stressed leaves, accompanied by a decrease in ACC 71 content, Eq. (29). 

Among the most noticeable findings from the research on plant hormones, the identification of receptors and receptor genes must be emphasized. In the last decade, since the publication of the previous edition of the book Comprehensive Natural Products Chemistry,5 the receptors and the receptor genes for ethylene, BRs, cytokinins, auxins, GAs, and abscisic acid have been identified, as described in the section for each plant hormone. 

Auxins (67), gibberellins (68), cytokinins (69), and abscisic acid (67) can enhance the production of ethylene if added in concentrations that are generally considered stronger than tissue levels. Paradoxically, ethylene was one of the first chemicals identified as a potent defoliant (70), and now it has been shown to be a natural product of plant tissues that seems to regulate abscission (68, 71) as well as an influence on a host of other physiological reactions (7). 

PLD plays important roles in the response to wounding and other stresses through mediating the actions and production of stress hormones [140]. PLDa is specifically involved in the actions of abscisic acid and ethylene in plant senescence and in the control of water loss [140, 141]. Different stresses in plants lead to different expression patterns for PLD isozymes. 

These variations in behavior indicate that harvesting melons at different stages of maturity causes subsequent biochemical events involved in amino acid accumulation to follow markedly different pathways. Recent work shows that melon fhiit harvested up to ten days before commercial maturity exhibits climacteric behavior with respect to ethylene production showing that at least this aspect of ripening is not completely inhibited by premature separation from the plant(P). However, the amount of ethylene produced is dependent on maturity at harvest and fruit harvested five days prematurely generated only about half of the amount of ethylene produced by fruit harvested two days before maturity. Also the lag time required to initiate ethylene production after harvest depended on maturity and was longer for prematurely harvested fruit. Changes in the content of the phytohormone abscisic acid were also correlated with that of ethylene. However whether the different maturity related metabolic responses observed above result from the action of these or other plant hormones awaits further study. 

Thus, cell enlargement, for instance, depends upon auxin and involves the uptake of water, extension of the cell membrane and protein synthesis. The auxin dose-response curve consists of two peirts promotion by low concentrations and inhibition by higher concentrations via the formation of ethylene. Cytokinins and abscisic acid may possibly induce also, under special conditions, the production of ethylene. Many publications deal with effects of these plant hormones, especially of auxin, on ethylene biosynthesis in plants which occurs after a lag phase of 30 - 60 minutes and is specifically blocked by rhizobitoxin as well as by inhibitors of ENA and protein synthesis indicating that a continuous synthesis of protein is required for high rate of ethylene production (Eef. 20). 

Andreae WA, Venis MA, Jursic E, Dumas T (1968) Does ethylene mediate root growth inhibition by indole-3-acetic acid Plant Physiol 43 1375-1379 Anker L (1973) The auxin production of the physiological tip of the Avena coleoptile and the repression of tip regeneration by indoleacetic acid (not by naphthylacetic acid and 2,4-dichlorophenoxyacetic acid). Acta Bot Neerl 22 221-227 Anker L (1975) Auxin-synthesis inhibition by abscisic acid, and its reversal by gibberellic acid. Acta Bot Neerl 24 339-347... 

Friedberg SH, Davidson D (1970) Duration of S phase and cell cycles in diploid and tetraploid cells of mixoploid meristems. Exp Cell Res 61 216-218 Fuchs Y, Lieberman M (1968) Effects of kinetin, lAA, and gibberellin on ethylene production, and their interactions in growth of seedlings. Plant Physiol 43 2029-2036 Gaither DH, Lutz DH, Forrence LE (1975) Abscisic acid stimulates elongation of excised pea root tips. Plant Physiol 55 948-949... 

Hiraki Y, Ota Y (1975) Relationship between growth-inhibition and ethylene production by mechanical stimulation in Lilium longiflorum. Plant Cell Physiol 16 185-189 Hiron RWP, Wright STC (1973) The role of endogenous abscisic acid in the response of plants to stress. J Exp Bot 24 769-781... 

Kohler K-H, Dorfler M, Goring H (1980) The influence of light on the cytokinin content of Amaranthus seedlings. Biol Plant 22 128-134 Kondo K, Watanable A, Imaseki H (1975) Relationships in actions of indoleacetic acid, benzyladenine and abscisic acid in ethylene production. Plant Cell Physiol 16 1001-1007... 

Letham DS (1971) Regulators of cell division in plant tissues. XII. A cytokinin bioassay using excised radish cotyledons. Physiol Plant 25 391-396 Libbenga KR, Xorrey JG (1973) Hormone-induced endoreduplication prior to mitosis in cultured pea root cortex cells. Am J Bot 60 293-299 Lieberman M, Kunishi AX (1971) Abscisic acid and ethylene production. Plant Physiol 47, Suppl, p 22... 

Mayak S, Dilley DR (1976) Regulation of senescence in carnation Dianthus caryophyl-lus) Effect of abscisic acid and carbon dioxide on ethylene production. Plant Physiol 58 663-665... 

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