ETHYLENE SENSITIVITY OF APPLE AND TOMATO FRUIT DURING THEIR DEVELOPMENT

Apple and tomato fruits were analysed for changes in sensitivity to et hylene during the later stages of their development. Dose-response stu dies were conducted by measuring in vivo activity of ACC-oxidase and C O2-production after treating the fruit with increasing concentrations of ethylene. ACC-oxidase activity of apple fruits was increasingly sti mulated by ethylene as fruit development progressed. Ethylene-stimulat ed respiration (CO2-production) on the other hand was hardly affected by the stage of fruit development. In contrast to apple fruits tomatoe s do not seem to undergo a significant change in their ethylene sensit ivity as far as the activity of ACC-oxidase and autocatalytic ethylene production is concerned. The ethylene concentration required for half maximal stimulation of ACC-oxidase activity and CO2-production was ca lculated to be 0.8 and 1.3 mul . l-1, respectively, and was almost ide ntical for apple and tomato fruits. The results are discussed in relat ion to several hypotheses of receptor-dependent phytohormone sensitivi ty.