| Four-year-old potted peachs "Prunus persica L.cv.Qingfeng"were adopted. The change of betaine content in the leaves of peach and the effects of exogenous betaine on physiological effect of peach were researched under water-stress. The main results were as follows: There was some content of betaine in the leaves of peach under natural water supply, and betaine in the leaves could accumulated under water-stress. With water-stress intensifying, the betaine content of the leaves of peach increased gradually under water-stress. Under water-stress, MDA content ,plasma mambrane permeality and the content of O2-and H2O2 in the leaves increased, and the activities of SOD,AsAPOD in the leaves changed. After spraying betaine in the leaves under water-stress, MDA content and plasma mambrane permeality in leaves could be decreased, and the activities of SOD,AsAPOD in the leaves could be increased, and the contents of O2-,H2O2 in the leaves could be decreased, in the end the damage to peach could be alleviated, and the drought resistance of peach was strengthened. The net photosynthetic rate of peach leaves declined under water-stress, the role of the stomatal limitation and the nonstomatal limitation leaded to the decline of Pn. The stomatal limitation was the main factor of the decline of Pn in the early period of stress , and the nonstomatal limitation was the main factor of the decline of Pn in the late period of stress. Pn of the peach leaves in the early period of stress was increased by spraying betaine in the leaves, and the time of the stomatal limitation was prolonged. The content of soluble sugar in the leaves was increased in the early period of stress and decreased in the late period of stress by spraying betaine in the leaves under water-stress. The drought resistance of peach was strengthened and the damage to peach could be alleviated by spraying betaine in the leaves under water-stress. And effect of 500 mg/L betaine was better than effect of 100 mg/L betanine.
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