THE MECHANISM INVOLVED IN ETHYLENE-ENHANCED ETHYLENE SYNTHESIS IN CARNATIONS

The plant hormone ethylene triggers and enhanced ethylene synthesis in certain ripening fruits and senescing flowers. Unlike most carnation (Dianthus caryophyllus L.) cultivars exhibiting climacteric rise in et hylene production at the onset of senescence, cv. Sandrosa does not sh ow this phenomenon naturally. In order to understand the mechanism of autocatalytic ethylene production, we exposed carnation flowers cv. Sa ndrosa to ethylene which resulted in an enhanced capacity for ethylene synthesis in the petals. A short time response of one hour was measur ed for an increase in ACC oxidase activity, about five hours in advanc e of an increase in ACC synthase activity and ethylene production. The observed enhancement was dependent on the presence of exogeneous ethy lene, and could be partially inhibited by prior treatment of the petal s with a-amanitin or cycloheximide. The results of the present study s uggest that in response to ethylene, activation of an existing enzyme is taking place first. This is followed by an increase in expression o f ACC oxidase and ACC synthase mRNAs.