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 f or 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 com pared in 'Fortune' mandarins. The HWT treatment increased CAT activity in t he fruit, but after they were removed from high temperature to cold storage a rapid decline in CAT activity was associated with increased chilling inj ury. Greater chilling tolerance and CAT activity was induced when fruits we re conditioned for 3 days at 37 degrees C and 90-95% RH. The CAT activity i n fruits exposed to HAT was higher than in the dipped and the non-heated fr uits 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 act ivity was reduced about two to three times by AT upon cold storage in the c ultivars 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 differen t effectiveness of the heat-conditioning treatments in increasing chilling tolerance of 'Fortune' mandarins may be related to induction of CAT activit y during heating and on its persistence during cold storage. (C) 2000 Elsev ier Science B.V. All rights reserved.