| Bagging is an effective measure to improve fruit appearance quality and it has been popularized recently in main apple-producing areas of China. However, the enclosed fruits, due to a considerable transition of microenvironments where they grow with higher temperature and humidity as well as poor ventilation, are subjected to a more stressed environmental condition. As a result, some severe physiological disorders arise, such as sunburn, black dots and superficial cracking, among which fruit sunburn (or precisely heat-related injury) in bags or after bag removal becomes the commonly vulnerable problem which usually takes place on the fruit epidermal tissues.By means of modern biological principles and methods, the present experiment was conducted to examine the characteristics of various microenvironments and antioxidative responses of fruit to those stresses with Red Fuji apples (Malus domestica Borkh.). The main results are as follows:1 Under natural conditions, the differences in solar radiation reception by the fruits and other ecological factors around them on different canopy exposures led to an obvious variation in fruit antioxidative capability. In sunny days during growing season, daily maximum fruit surface temperature appeared on the fruits from south exposure, 8.8℃ higher than the average of those from north, northeast, east and northwest exposures. However, the bagged fruits, influenced by their microenvironments, had a fruit surface temperature 10.3℃ higher than those from north, northeast, east and northwest exposures. The experiments also showed that the maximal fruit temperatures, regardless of bagged of naked fruits, appeared on the southwest quadrant canopy owing to more reception of solar radiation, so that a severer stress could be expected, exhibiting a marked rise in (V and MDA contents as well as SOD and POD activities. It was proved that the surface temperatures of fruits with bags were consistently higher than those from the control. Enclosed fruits stressed by high temperatures and other ecological factors had a higher level of O2: and MDA contents, thus being responsible for a rise of SOD and POD activity within a certain range.2 Different types of bags could create various microenvironments for apples so that some significant differences were found in both fruit temperatures and light reception. Themaximum fruit temperature was detected with black paper bags and the minimum with newspaper bags. Meanwhile, there was almost no light within double-layered bags, very weak light with black paper bags, lower-intensity light with red and newspaper bags, and intense light (approximately close to natural light) with white and yellow plastic bags. The activities of 5'-nucleotidase, SOD and POD as well as the contents of O2 and MDA varied with different types of fruit bags with maximal contents of both O2 and MDA and minimum activities of SOD and POD accompanied with white plastic bags. However, higher activities of SOD and POD and lower contents of O2 and MDA were found with double-layered bags possibly because of their better performance of holding warmth, poor exchange of heat between interior and exterior environments and relatively stable temperatures so that fruit could get somewhat acclimation within bags.3 The effect of temperature fluctuations on fruit oxidative capability varied with different modes of temperature changes. As the treatments with a temperature rising of either 25℃→30℃→40℃→ 48 ℃ or 24℃→45℃→25℃→48℃ were designed to increase fruit temperatures slowly and gradually so that fruit might get acclimated, the SOD and POD activities in fruit peel tissues rose significantly with a corresponding decline in Or and MDA contents. Whereas the treatment of temperature rising from 25 ℃ directly to 48 ℃ in a short period of time resulted in the highest levels of O2- and MDA, even though SOD and POD activities increased slightly.4 Application of exogenous AOS agents could alter the contents of endogenous activated oxygen species contents in fruit peel...
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