Superoxide dismutase and catalase activities in apple fruit during ripening and post-harvest and with special reference to ethylene

Oxidative stress is involved in many biological systems, among which are fruit ripening and senescence. Free radicals play an important role in senescence and ageing processes. Plants have evolved antioxidative strategies in which superoxide dismutase (SOD, EC 1.15.1.1) and catalase (CAT, EC 1.11.1.6) are the most efficient antioxidant enzymes, influencing patterns of fruit ripening. Variations in total SOD and CAT activities were determined at regular intervals during ripening and senescence in on-tree and cold-stored apple fruits of the cultivars Fuji and Golden Delicious. In all fruits, internal ethylene concentration was also measured. The results suggest that the onset of ripening, signalled by ethylene burst, is closely related to SOD and CAT activities. In on-tree fruits the climacteric peak in ethylene was associated with the peaks of SOD and CAT activity in both cultivars. Quite different results were obtained in cold-stored fruits: Ethylene concentration increased in both cultivars during the storage. CAT activity doubled in both cultivars. SOD activity decreased in Golden Delicious and peaked in Fuji.