Effect Of High-temperature And Excessive-light Stresses On Antioxidant Capacity In Apple Fruits

Apple fruit sunburn, a common physiological disorder, happens widely in main apple-producing areas in the world and results in a huge loss annually. With gradual popularization of dwarf rootstocks adaptable to native conditions in China, dwarf and compact culture will become a general trend of apple production inevitably. Coupled with the seriously prevailing tendency of global warming day by day, it could be expected that the injury caused by high temperatures and excessive light will be aggravated in the near future, and this disorder will become a severe problem which undoubtedly affects the apple industry in China, and thus it is necessary to intensify the studies on the prevention and the mechanism of fruit sunburn in advance.Using the principles of resistance physiology and advanced technologies in laboratories and field trials, the project was undertaken to reveal the patterns of antioxidant properties of exogenous antioxidants on the anti-fruit oxidation characteristics, the responses of Fuji apples to the stresses caused by high temperature and excessive light. As a consequence, the features of sunburn occurrence and the effect of different exogenous chemical application on antioxidant capability have been documented. The main results are as follows:1 Browning fruit had a higher relative conductivity and LOX activity compared to the normal fruit, and browning fruit also had higher antioxidant (AsA and GSH) contents and higher activities of antioxidant enzymes (APX, GR, and MDHAR). The ratio of AsA / DHA with browning fruits was significantly smaller than that with normal ones. The fruits enclosed with plastic bags, compared with the fruits covered with double-layer paper bags, had a higher electrolyte leakage and LOX activity and also had higher antioxidant contents and antioxidant enzyme activity.2 The relative conductivity, LOX activity, antioxidant content and antioxidant enzyme activities in the fruit peels were responsive to heat stress extents. At 35℃, the antioxidant contents and antioxidant enzymes activity were significantly higher than the control, and with time prolonged, there was a decline trend. At 45℃heat treatment, only for 1h various antioxidants and antioxidant enzymes increased , followed by a rapid decline of antioxidants, significantly lower than the control. There was no significant difference between heat treatment and the control. It was suggested that 35℃heat treatment was favorable to the improvement of heat resistance induced by fruit.3 With respect to different exposures on a canopy and different fruit surfaces, the antioxidant contents and antioxidant enzyme activities were quite different. Among eight different exposures on a canopy, the fruits in the southwest direction at 14:00 had the highest relatively conductivity and LOX activity, and fruits in southwestern direction also had higher antioxidant contents and higher activities of antioxidant enzymes.4 Different types of exogenous antioxidants had a stimulating effect on improving the antioxidant capacity of membranes in fruit surface cells, and they can effectively improve the activity of protective enzymes and endogenous antioxidant contents and reduce the electrolyte leakage and LOX activity. It was proven that the treatments with CaCl2 and VE showed an insignificant improvement.