Nonosmotic Inhibition by Sugars of the Ethylene-Forming Activity Associated with Microsomal Membranes from

The activity of the membrane-bound ethylene-forming enzyme, previously reported in carnation (Dianthus caryophyllus L. cv White Sim) petals (Mayak, Legge, Thompson 1981 Planta 153: 49-55), is inhibited by sugars. Of the various sugars tested, sorbitol was the most effective and glucose the least. The effect of sugars was also evaluated on solubilized ethylene-forming enzyme activity, obtained by the use of 0.6% Nonidet NP-40 detergent. Similar to the membrane-bound activity, the solubilized activity was also inhibited. Kinetic studies revealed that the inhibition by sugars is reversible, and that inhibition by sucrose is uncompetitive while that by sorbitol is competitive. During senescence of petals, a decline in sugar content and climacteric like increase in ethylene occurs. Hence, the physiological relevance of sugar inhibition and its possible involvement in the regulation of ethylene biosynthesis is suggested. Interrelationships between sugars and ethylene have been widely reported. Ethylene application was found to affect sucrose distribution in carnation flower parts (16), and exogenous sucrose application has been shown to reduce the sensitivity of flowers toward ethylene (12). In addition, sucrose content of petals declines toward senescence which is accompanied by a climacteric-like burst of ethylene production (15), and exogenous sucrose delays senescence and the associated rise in ethylene production (7).