[Effects of exogenous betaine on physiological responses of peach tree under water stress]

With four-year-old potted Prunus persica L. cv. Qingfeng as test material, this paper studied the change pattern of its leaf betaine content under water stress, and its physiological responses under effects of foliage-spraying exogenous betaine. The results showed that under normal water supply, the betaine content in Qingfeng' s leaf was 75.9-80.5 microg x g(-1) FM, which was increased with increasing water stress, and up to 278.9 microg x g(-1) FM on the 16th day after cutting off the water supply. The leaf plasma membrane permeability was 8.06% - 8.61% under normal water supply, but increased to 28.62% under water stress. When 100 and 500 mg x L(-1) of betaine were applied exogenously, the plasma membrane permeability was 26.25% and 21.79% after 16 days, respectively. The hydrogen peroxide (H2O2) content increased from 27.2-32.5 micromol g(-1) FM to 76.4 micromol x g(-1) FM in the course of water stress, and decreased to 73.2 and 68.5 micromol x g(-1) FM after spraying 100 and 500 mg betaine x L(-1), respectively. During the period of intensified water stress, the peak value of ascorbate peroxidase (AsA-POD) activity was 0.435 mg x g(-1) FM, and up to 0.490 mg x g(-1) FM when treated with exogenous betaine. When the peach tree was subjected to water stress, the contents of free proline and soluble sugar accumulated dramatically, but produced on approximately decrease in 500 mg x L(-1) endogenous betaine application on the 16th day which was slightly less than that of control and 100 mg x L(-1) betaine application. There was a gradual decline in the content of soluble protein under water stress, and an increment of 20. 3% was observed when betaine was applied exogenously. These results strongly suggested that foliage-spraying exogenous betaine could increase the drought resistance of peach tree through decreasing its leaf plasma membrane permeability and H2O2, free proline and soluble sugar contents and increasing its leaf AsA-POD activity and soluble protein content.