Lipoxygenase (LOX) activity was assayed in various parts of tomato (Lycoperiscon esculentum cv. Caruso) fruits, after harvest and at different stages of ripening. Lipoxygenase activity reached a peak at the turning stage of ripeness in the pericarp and radical pericarp tissue. The changing pattern of C_2H_4 production in different tomato fruit tissues at different stages of ripeness closely followed that of LOX activity. Application of linolenic acid and linolenic acid to tissue slices of tomato fruit promoted ethylene production. This effect was specific to unsaturated fatty acids which serve as substrates for lipoxygenase action, and did not occur following similar treatments with saturated fatty acids (palmitic acid and stearic acid). Two major lipoxygenase pathway metabolites, including jasmonic acid and traumatic acid, also promoted ethylene production by tomato fruits. Treating fruits with lipoxygenase inhibitors (n-propyl gallate, nordihydroguariaretic acid), inhibited ethylene production. These results suggest that lipoxygenase activity and jasmonates were involved in the ripening of tomato fruits. The possible way in which LOX is involved in ethylene biosynthesis is discussed.
展开▼
