ETHYLENE SENSITIVITY OF APPLE AND TOMATO FRUIT DURING THEIR DEVELOPMENT

Apple and tomato fruits were analysed for changes in sensitivity to ethylene during the later stages of their development. Dose-response studies were conducted by measuring in vivo activity of ACC-oxidase and CO2-production after treating the fruit with increasing concentrations of ethylene. ACC-oxidase activity of apple fruits was increasingly stimulated by ethylene as fruit development progressed. Ethylene-stimulated respiration (CO2-production) on the other hand was hardly affected by the stage of fruit development. In contrast to apple fruits tomatoes do not seem to undergo a significant change in their ethylene sensitivity 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 calculated to be 0.8 and 1.3 mul . l-1, respectively, and was almost identical for apple and tomato fruits. The results are discussed in relation to several hypotheses of receptor-dependent phytohormone sensitivity.