José M. Sala

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

Abstract The effect of a postharvest hot-water dip treatment (HWT) at 53°C for 3 min and a 3-day heat-conditioning treatment at 37°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°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°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°C but not at 12°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.

Effect of specific and non-specific stimuli on the visual and motor cortex of the rat.

Summary In order to study the possible simultaneous influences of light and darkness, and mobility and restraint on the visual and motor areas of the cortex, we have studied the visual and motor cortex of 4 groups of rats raised under the following conditions: (1) in normal light conditions and large cages; (2) in normal light conditions and cages small enough to restrain the movement of the animals; (3) in total darkness and large cages and (4) in total darkness and small cages. They were kept in these conditions from weaning until they were 90 days old. At this time they were killed and their brains stained following the rapid Golgi procedure. The spines along the apical shaft of the pyramidal neurons of layer V of the visual and motor cortex (a total of 20–25 cells/group) were counted. The results were processed in a PDP 11/40 computer. While darkness produced a decrease in the mean number of dendritic spines of only the visual cortex, restraining the animal produced a significant decrease in the mean number of spines in both cortices, motor and visual. Furthermore, the influence of restraining was found so strong on the visual cortex that it masked the effect of darkness. There was no significant difference between the mean number of spines per shaft of animals held restrained and in light, versus animals held restrained and in darkness. These results indicate that movement itself is very important for the correct development of dendritic spines in the visual cortex.