Regulation by carbon dioxide of wound-induced ethylene biosynthesis in tomato pericarp and winter squash mesocarp tissues

The effects of CO₂ treatment on wound-induced ethylene biosynthesis were investigated in excised pericarp and mesocarp tissues of tomato (Lycopersicon esculentum Mill. cv. TVR-II) and winter squash (Cucurbita maxima Duch. cv. Ebisu) respectively. Wounding caused increase in ethylene production rate, the levels of 1-aminocyclopropane-1-carboxylic acid (ACC) and 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC) and the activities of ACC synthase and ACC oxidase. The increase in the rate of ethylene production and ACC synthase activity were suppressed by CO₂ treatment and was dependent on CO₂ concentration. CO₂ treatment also suppressed wound-induced increase in ACC level irrespective of the CO₂ concentration. The presence of 10% CO₂ had no effect on ACC conjugation to MACC induced by wounding while 60% CO₂ suppressed almost completely ACC conjugation. CO₂ promoted and inhibited induction of ACC oxidase activity in excised tomato and winter squash tissues respectively. These results suggest that CO₂ inhibits wound-induced ethylene biosynthesis by reducing the availability of ACC through repression of ACC synthase synthesis and/or inhibition of its activity. Also endogenous ethylene produced in response to wounding may play a role in the regulation of wound-induced ethylene production.