Biosynthesis of Wound Ethylene 1

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Untreated mung bean hypocotyls produced very little C2H4 but, upon treatment with 10 millimolar Cu2+ or 10 millimolar Cu2+ + 10 millimolar Ca2+, C2H4 production increased 20- and 40-fold, respectively, within 6 hours. This increase in C2H4 production was preceded and paralleled by an increase in 1-aminocyclopropanecarboxylic acid (ACC) content, but the level of S-adenosylmethionine (SAM) was unaffected, suggesting that the conversion of SAM to ACC is a key reaction in the production of wound-induced C2H4. This view was further supported by the observation that application of aminoethoxyvinylglycine, a known inhibitor of the conversion of SAM to ACC, eliminated the increases in ACC formation and in C2H4 production. A significant increase in C2H4 production was observed in the albedo tissue of orange in response to excision, and it was paralleled by an increase in ACC content. In columella tissue of unripe green tomato fruit, massive increases in the C2H4 production rate (from 0 to 12 nanoliters per gram per hour), in ACC content (from 0.05 to 12 nmoles per gram), and in ACC synthase activity (from 0 to 6.4 units per milligram protein) occurred during the 9-hour incubation period following excision. Infiltration with 0.1 millimolar cycloheximide, an inhibitor of protein synthesis, completely blocked wound-induced C2H4 production, ACC formation, and development of ACC synthase activity. These data indicate that wounding induces the synthesis of ACC synthase, which is the rate-controlling enzyme in the pathway of C2H4 biosynthesis and, thereby, causes accumulation of ACC and increase in C2H4 production.

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