Catalase in the heat-induced chilling tolerance of cold-stored Hybrid Fortune mandarin fruits

Hybrid Fortune mandarins developed chilling injury (CI) upon cold storage, unless the fruits were conditioned at 37 degrees C for 3 days before they w ere held at low temperature. This heat treatment induced 2.5-, 1.2-, and 1. 4-fold increases in the activities of catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD), respectively, and reduced the activi ty of glutathione reductase (GR). The differences in the activities afforde d by the heat treatment were, in general, maintained during cold storage. H owever, SOD levels in nonconditioned Fortune fruits exhibiting CI were simi lar to those of conditioned fruits stored for 0 or 6 weeks at 2 degrees C. No difference between APX activity in the conditioned and nonconditioned fr uits stored for 6 weeks at 2 degrees C was found. The data indicate that CA T may be a major antioxidant enzyme operating in the heat-induced chilling tolerance of cold-stored Fortune mandarin fruits.