Catalase enzyme activity is related to tolerance of mandarin fruits to chilling

The effect of a postharvest hot-water dip treatment (HWT) at 53 degrees C for 3 min and a 3-day heat-conditioning treatment at 37 degrees C with air (HAT) at 90-95% RH on chilling tolerance and catalase (CAT) activity was compared in 'Fortune' mandarins. The HWT treatment increased CAT activity in the fruit, but after they were removed from high temperature to cold storage a rapid decline in CAT activity was associated with increased chilling injury. Greater chilling tolerance and CAT activity was induced when fruits were conditioned for 3 days at 37 degrees C and 90-95% RH. The CAT activity in fruits exposed to HAT was higher than in the dipped and the non-heated fruits over the storage period at 2 degrees C. An inhibitor of CAT activity, 3-amino-1,2,4-triazole (AT), caused peel damage in HAT 'Fortune' mandarins and in the chilling-tolerant 'Clementine' and 'Clemenules' cultivars stored at 2 degrees C but not at 12 degrees C (non-chilling temperature). CAT activity was reduced about two to three times by AT upon cold storage in the cultivars studied. Little difference was found in the activity of ascorbate peroxidase (APX), glutathione reductase (GR) and superoxide dismutase (SOD) between AT-treated and non-treated fruits. The data indicate that CAT may be a major antioxidant enzyme involved in the defence mechanism of mandarin fruits against chilling stress. Our results also suggest that the different effectiveness of the heat-conditioning treatments in increasing chilling tolerance of 'Fortune' mandarins may be related to induction of CAT activity during heating and on its persistence during cold storage. (C) 2000 Elsevier Science B.V. All rights reserved.