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 were 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 activity of glutathione reductase (GR). The differences in the activities afforded by the heat treatment were, in general, maintained during cold storage. However, SOD levels in nonconditioned Fortune fruits exhibiting CI were similar 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 fruits stored for 6 weeks at 2 degrees C was found. The data indicate that CAT may be a major antioxidant enzyme operating in the heat-induced chilling tolerance of cold-stored Fortune mandarin fruits.