RELATIONSHIP BETWEEN STRESS ETHYLENE PRODUCTION INDUCED BY GAMMA-IRRADIATION AND RIPENING OF CHERRY TOMATOES

Changes in ACC metabolism induced by gamma irradiation have been studied during ripening of cherry tomatoes (Lycopersicon esculentum L. cv. Sweet 100) treated at the mature-green stage. Irradiation caused a sharp and transient dose-dependent increase in ethylene production during the first 24 hours that was associated with an increase in ACC synthase activity. The activity of ethylene-forming enzyme (EFE) was also stimulated but was never limiting. Nine days following irradiation, ACC metabolism was more active in irradiated fruits, with ACC being mainly directed to ethylene [80% at 3 kilogray (kGy; 1 Gray = 100 Rad = 1 J.kg-1)] rather than to malonyl ACC (MACC). As a consequence, fruit ripening was accelerated. For doses < 1 kGy, the time required for 50% of the fruits to reach breaker stage (the onset of climacteric ethylene production) was inversely correlated with radiation dose and the amount of stress ethylene produced during the first 24 hours. At doses > 1 kGy, in spite of a continuous stimulation of stress ethylene production, no additional acceleration of ripening occurred. At 3- to 5-kGy doses, fruit ripening was impaired transiently with a fast subsequent recovery. As a result, a significant synchronization of fruit ripening (presumed to be caused by enhanced ethylene production) was observed. Chemical names used: I-amino-cyclopropane-1-carboxylic acid (ACC).