Wound ethylene production

Plants under water stress are known to produce increased amounts of ethylene, show a rise in ABA and a decline in endogenous cytokinins (52,53). Other plant hormones are also probably involved in the response to water stress and other stress and wounding actions. The surge of ethylene production upon stress may therefore represent a response to a disturbance of the hormonal balance in tissues. The dampened oscillation curve for wound ethylene production may reflect the dynamic return of the disturbed hormonal system to a proper hormonal balance under the new tissue conditions, and thus may also reflect a healing phenomenon. 

Fig. 1. Ethylene biosynthesis. The numbered enzymes are (1) methionine adenosyltransferase, (2) ACC (l-aminocyclopropane-l-carboxylic acid) synthase, (3) ethylene forming enzyme (EFE), (4) 5 -methylthio-adenosine nucleosidase, (5) 5 -methylthioribose kinase. Regulation of the synthesis of ACC synthase and EFE are important steps in the control of ethylene production. ACC synthase requires pyridoxal phosphate and is inhibited by aminoethoxy vinyl glycine EFE requires 02 and is inhibited under anaerobic conditions. Synthesis of both ACC synthase and EFE is stimulated during ripening, senescence, abscission, following mechanical wounding, and treatment with auxins.

Fig. 4. Ethylene production by wounded leaves and ripening fruit of normal tomato plants and those transformed with EFE (pTOM 13) antisense genes. A, Ethylene production by wounded leaves of plants with none ( ), 1 (O), or 2 ( ) antisense genes B, ethylene production by ripening fruit from plants with none ( ), 1 (O), or 2 ( ) antisense genes (after Hamilton et al., 1990).

Figure 6. Profile of ethylene production by wounded stems of etiolated pea seedlings. The profile shows kinetic changes suggesting dampened oscillation (from Saltveit and Dilley (50))...

Immunochemical and fluorographic analysis of in vitro translation products of mRNAs from fresh and wounded tissues of winter squash mesocarp [59] and tomato pericarp [60,164] clearly provide evidence for the transcriptional control of ACC synthase. Translatable mRNA for ACC s3mthase is not detectable in fresh tissue, but increases dramatically after wounding with a lag period of a few hours. Time course profiles of ethylene production after wounding, ACC synthase activity and the relative abundance of the mRNA after wounding are well correlated with each other. 

An important characteristic of ACC synthase in plant tissues is its lability. It has been well recognized that when ethylene production in plant tissues is induced by lAA treatment or by various stresses [33], ethylene production declines rapidly following induction, and this decline is accompanied by a corresponding decline in ACC content. Two mechanisms are responsible for this rapid decline in ethylene production one is the conjugation of ACC into MACC catalyzed by ACC malonyltransferase resulting in a reduced ACC level in the tissue, and the other is the inactivation of ACC synthase. The apparent half-life of ACC synthase in wounded green tomato pericarp and in lAA-treated mungbean hypocotyls has been estimated to be 30-50 min, based on the decay kinetics of the enzyme activity extracted from induced tissues in the presence of cycloheximide which blocks the new synthesis of the enzyme [1, 36]. 

Although these data call into question ethylene s present position as the do it in almost all plant hormone, there is no denying the manifold effects of applied ethylene in plant growth and development. For many years ethylene itself has been used commercially to elicit some of these effects, for example, fruit ripening. Compounds which initiate ethylene responses by inducing the plant to produce its own ethylene (a wound response) have been used in the field. Cycloheximide application, for example, stimulates abscission of citrus by stimulating ethylene production at the button [15]. The possibilities for harnessing ethylene responses in... 

Wounding is assumed to exert its effect at the step where SAM (=S-adenosylmethionine) is converted into ACC (1-aminocyclopropane-l-carboxylic acid), the direct precursor of ethylene. Normally this step, regulated by the enzyme ACC synthase, is rate-limiting in the cascade of events leading to ethylene production (Yang and Hoffman 1984). By means of stress the rate can be increased... 

Worm end products, 18 646 Worsted wool-processing system, 26 383-384, 385-386 Worsted yarn, 11 178 Wort, 3 563, 564, 574, 575, 583 separation, 3 578-579 Wound closure, suture size and, 24 216 Wound closure biomaterials, 24 205. See also Sutures Wound dressings cotton smart, 3 31 ethylene oxide polymers in, 10 687 hydrogels in, 13 751-752 Woven fabrics, 11 178 dyeing, 9 170-171 Woven flax fibers, 11 594 Woven plastic bags, 18 12 Wovens... 

JA and ethylene act synergistically in response to wounding.199 Arimura et al200 found that lima bean plants infested with two-spotted spider mites ( T. urticae) showed emission of ethylene. Synergistic effects of ethylene on JA-induced volatile production in lima bean leaves are reported.2 1... 

Aminocyclopropane carboxylic acid (6) has been detected in several plant tissues a procedure for preparing 6 from agricultural wastes, by extraction with a diluted solution of sulfosalicylic acid, has been described . 6 was established to be an intermediate product in ethylene biosynthesis " . Ethylene acts as a phytohormone which is involved in many metabolic processes in plants, e.g. in ripening, in stress situations or after wounding (see review and references cited therein). Natural 6 is formed from methionine via sulfonium salt (640) only S,S-(640) acted as a substrate for aminocyclopropanecarbo-xylate synthase, the S,R and R,R isomers of 640 were inactive as substrates . 6 can be... 

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. 

Polymers used in nontoxic sterilizable items, such as tubing, artificial organs, and wound coverings, must be able to withstand sterilization by ethylene oxide, steam autoclave, or gamma radiation. For medical products sterilized by gamma irradiation, only plastics that do not degrade or discolor on exposure to radiation, such as polyester and polycarbonates, can be used. 

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