Effects Of Zinc Sprays On Phytohormones Concentration And Activities Of Sugar Metabolism Enzymes In Apple Fruits

Experiments were conducted in 2013 and 2014 using 14-year-old Fuji apple trees(Malus×domestica Borkh. Red Fuji/M. hupehensis Rehd.) in an orchard in chaoquan(latitude 36°14’N; longitude 116°50’E), Feicheng County, Tai’an, Shandong Province, China. Normal tree and Zn-deficient trees(‘rosette tree’) under the same growth conditions and the same management level were selected and were sprayed 2% Zn concentration before budbreak. Four kinds of mineral elements content and sugar content of developing fruits were measured. The responses of phytohormones for zinc sprays were studied and we explored their influence on carbohydrate metabolism-related enzyme activity, in order to illuminate the physiological mechanism of zinc on apple fruit quality. The main results are as follows:(1) Spraying Zn on normal and rosette trees both increased the Zn concentration in fruit. Spraying Zn on apple trees significantly increased the Zn concentration of young fruit in 2013 year. While the 2014 data showed that fruit Zn concentration significantly improved in the whole developmented process excepted 105 DAFB. Spraying Zn on apple trees reduced the iron content in young fruit. Spraying Zn on normal and rosette trees both increased the Ca concentration in mature fruit. Results showed that spraying Zn on apple trees had no significant effect on fruit in potassium content.(2) Spraying Zn significantly improved the IAA content of seeds and flesh of apple fruits. The concentration of IAA was significantly improved at 15, 105, and 165 DAFB of apple seeds while this of apple flesh of was significantly increased at 45, 105, and 165 DAFB after spraying Zn in 2014 years. Results showed that spraying Zn on apple trees significantly increased the GA3 concentration at 45 DAFB, which promoted the growth of young fruit. The ABA concentration was decreased in young fruit and increased at 135 and 165 DAFB, while the effect of spraying Zn on the ABA content of flesh was showed at full-ripening stage.(3) Activities of carbohydrate metabolic enzymes in apple fruits were affected by spraying zinc. The effects on the activities of sucrose synthase-cleave(SS-c) and acid invertase of spraying Zn were showed in young fruit and promoted the decomposition of sucrose to hexose for young fruit growth. Spraying Zn improved the activity of sucrose phosphate synthase in matrue fruit and promoted sucrose synthetase in fruit. The effect on the activity of sorbitol oxidase showed at young fruit stage, and for sorbitol dehydrogenase, spraying Zn improved the activity of SDH at enlargement and mature fruit stages.(4) Spraying Zn on normal and rosette trees both increased the fruit soluble sugar content. The soluble sugar content was increased significantly at at fruit enlargement and mature stages in 2013 year, while in 2014 year, spraying Zn significantly improved the fruit soluble sugar content in the whole developmented process. For frucose and reducing sugar, spraying Zn increased the content of frucose and reducing sugar at fruit enlargement and mature stages. Fruit glucose content was significantly improved in young furit and mature fruit by spraying zinc in 2013 year. After spraying zinc with two consecutive years, fruit glucose concentration was significantly improved the at all the development stages but the 45 DAFB. For sucrose, the fruit frucose content at enlargement and mature stages was increased with spraying zinc. Results showed that RT+Zn significantly decreased the fruit strach concentration at all the development stages.(5) These correlations between concentrations of phytohormones and activities of sugar metabolic enzymes indicated that IAA, GA3 and ABA concentration could control sucrose and sorbitol turnover through the regulation of SS-c, AI, and SOX at fruit early stage. IAA, ABA concentration and SPS, SDH activities were positively correlated indicating that an increase in sucrose synthesis and sorbitol transforming to fructose at fruit expansion stage. A highly significant positive correlation was observed between ABA concentration and SDH, SOX activity, indicating that a high level of ABA significantly increased SDH and SOX activity and promoted sorbitol turnover at fruit mature stage.(6) The weight of single fruit, soluble solids and anthocyanin content wrer significantly increased, and the titratable acidity and fruit firmness decreased by spraying zinc. There was no significant effect on fruit Vc concentration with spraying Zn. The effect of spraying Zn two consecutive years on improving fruit quality compared with that of one year was obvious.