Zinc sulfate spray increases activity of carbohydrate metabolic enzymes and regulates endogenous hormone levels in apple fruit

- Zinc spray before bud break changed the content of some kinds of sugar in fruit.
- The treatment improved some carbohydrate metabolic enzymes in fruit.
- The treatment increased indole acetic acid and gibberellin content in fruit seeds.

The application of zinc sulfate (ZnSO4) were conducted during two years on fourteen-year-old 'Fuji' apple trees before budbreak. The effects of zinc sulfate application on Zn contents, activities of carbohydrate metabolism enzymes, contents of endogenous hormones and carbohydrate in apple fruit at different development stages were investigated. The treatment significantly increased the Zn contents of fruit. The treatment significantly decreased sucrose content of fruit at fruit expansion stage and increased its content of fruit at fruit mature stage; the treatment significantly increased fructose content and glucose at fruit expansion stage and mature stage; the treatment decreased sorbitol at young fruit stage and expansion stage significantly. The activities of sucrose synthase (SS), sorbitol dehydrogenase (SDH) and acid inverts (AI) in fruit of trees treated were significantly higher than the control at young fruit stage and expansion stage. Sucrose phosphate synthase (SPS) activities in fruit of treated trees were significantly higher than that of the control during fruit mature stage. The treatment increased the content of indole acetic acid (IAA) and gibberellin (GA3) in fruit seeds significantly at young fruit stage. The treatment significantly reduced the contents of abscisic acid (ABA) in seeds of fruit at young fruit stage and significantly increased ABA content during fruit mature stage. Spraying ZnSO4 enhanced the fruit Zn content, which resulted in the higher activities of carbohydrate metabolism-related enzymes (SDH, AI, SS, SPS) and regulated IAA, GA3 and ABA levels, contributing to the accumulation of carbohydrate in fruit.