SUPEROXIDE-DISMUTASE ACTIVITIES IN SENESCING APPLE FRUIT (MALUS-DOMESTICA BORKH)

Total superoxide dismutase (SOD:superoxide: superoxide oxidoreductase; EC 1.15.1.1) activity and individual activities of its three different metalloenzymes, CuZn-SOD, Fe-SOD, and Mn-SOD, were investigated during senescence of apples (Malus domestica Borkh.). Total SOD activity and relative activities of its three forms varied greatly among cultivars. Activities underwent considerable change during senescence of fruit, but changes were different among cultivars. Whether fruit senesced at 0 degrees C or 20 degrees C had little effect on SOD activities, and application of the antioxidant diphenylamine (DPA) did not alter activities. SOD activities increased with occurrence of the physiological disorder ''senescent breakdown,'' but did not increase with occurrence of the disorder ''superficial scald.'' In a given apple cultivar, changes in total SOD activity generally paralleled activities of the different SOD forms. Such activity may reflect changes affecting food and nutritive quality of the fruit.