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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.

The effects of applying ethylene (2 microL x L(-)(1)) during cold storage of Fortune mandarins on the development of chilling-induced peel damage and on changes in the activities of the enzymes of the antioxidant system, superoxide dismutase, catalase (CAT), ascorbate peroxidase, guaiacol peroxidase, and glutathione reductase, and on phenylalanine ammonia-lyase (PAL) have been investigated. Chilling damage was reduced by applying ethylene during fruit storage at 1.5 degrees C. PAL activity increased in response to cold stress and was higher in fruit held under ethylene than under air during the whole storage period, whereas CAT was temporarily higher in ethylene-treated fruit. In contrast, the activities of the other enzymes were not increased by ethylene. The global results suggest that the ethylene-induced chilling tolerance in Fortune mandarins might be due to increased PAL and CAT activities.

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Changes in the content and chemical composition of epicuticular wax of susceptible and non-susceptible ' Navelina' orange and non-susceptible 'Satsuma' mandarin fruits to rindstaining, growing in the area of Valencia (Spain), were studied. The epicuticular wax content of the susceptible Navelina fruits increases with ripening from 30 pg in July to 110 pg cnrZ in January. The epicuticular wax content of the non-susceptible Navelina fruits was similar to that of the susceptible ones. The epicuticular wax content of the Satsuma mandarin fruits was lower than that of Navelina orange fruits; it changed from 20 pg in July to 40 pg cm-z in January. In this study, no correlation between epicuticular wax content and susceptibility to rindstaining of the orange fruits was found. In general, alkanes, aldehydes and fatty acids are the major wax constituents, whereas the primary alcohols and the triterpenoids are the minor ones. The maximum incidence of rindstaining occurs at the end of October and the beginning of November, immediately after the major rate of increase of the fruit surface. Such an increase also concurs with the major hardening and facility of cracking of the wax layer.