Abstract: Zn was sprayed on thirteen-year-old‘Fuji’apple trees at different developmental stages. The effects of Zn on Zn contents of fruits，reducing sugar content and activities of carbohydrate metabolism-related enzymes were investigated. The results showed that the Zn treatments significantly increased the Zn contents and the reducing sugar in fruits at mature stage. The activity of sorbitol dehydrogenase（SDH）was significantly higher in the fruit of apple trees treated prior to bud break and at three weeks after bloom than the control at young fruit stage. The SDH activity of the fruit treated when the spring shoots stopped growth was higher than the control during fruit expansion period. The fruit treated at fruit expanding stage showed higher SDH activity than the control during fruit mature stage. The sorbitol oxidase（SOX）activity of all the treatments was not significantly different compared with the control. The Zn treatment did not show significant effects on sorbitol oxidase（SOX）activity of fruits. The Zn treatments before bud break and at three weeks after blooming significantly increased the activities of sucrose synthase（SS）and acid inverse（AI）at young fruit stage. The Zn treatments at fruit expanding stage significantly increased the activity of AI at mature stage，while there were no effects on the activity of neutral inverse（NI）. Our results showed Zn treatments enhanced the biofortification of fruit Zn，which resulted in the higher activities of carbohydrate metabolism-related enzymes and the accumulation of sugar in fruits.

Key words: apple, Zn, reducing sugar, sorbitol metabolism enzymes, sucrose lyase