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.