Zinc Distribution Characteristics And Influence Of Organic Acid On Zinc Distribution In Apple Tree Under Zinc Stress

Zinc (Zn) is an essential micronutrient for various physiological and metabolic processesin plants. The apple is sensitive to Zn stress which can limit apple yield and nutritional quality.Root high proportion of unavailable Zn may relate to Zn subcellular distribution and chemicalforms in apple tree. The organic acid was the intermediate products of carbon metabolism,and mainly as ligand substances involved in the absorption and distribution of heavy metals inplants. The apple tree is a perennial woody plant. The organ has characteristics of developingevery other year and successive nutritional storage. The nutritional metabolic processes arecomplex. It is important to study the relationship between organic acid and Zn distribution forZn regulation mechanism in apple tree under Zn stress.Apple cultivar field of prosperous ‘Fuji’, Malus hupehensis Rehd and Malus xiaojinensisCheng et Jiang were selected which were cultured with distilled water as materials to study thecharacteristics of Zn distribution in every organ and influence of organic acid on Zndistribution under Zn stress and explore the relationship between organic acid and Zndistribution in apple tree. The main results were as follows:(1) The Zn concentrations in the rosette roots and the normal roots were significantlydifferent: the rosette roots showed a rise-and-fall pattern, but the normal roots kept Znconcentrations at a litter high stable level. Zn concentrations of the rosette roots reached thelowest point of the whole year at spring-shoot growth stopping stage, but were higher than thenormal roots in most phenophase periods.(2) Organic acid concentrations of all apple roots gradually increased in the early stageand showed the highest level at autumn-shoot fast growing stage, and then immediately fell toa stable level. There was a higher organic acid concentration in the rosette roots than thenormal roots in all phenophase periods; Zn and organic acid concentrations showed asignificantly negative correlation at spring-shoot growth stopping stage, but a positive correlation in other phenophase periods and was the most closely related to the malate.(3) The subcellular distribution of apple thin roots was significant different annually,while relatively stable in the thick roots. Zn concentration and relative proportion in the cellwall and the vacuole were the highest in most phenological periods annually. Zn in rosettethin roots was mainly located in the vacuole, followed by the cell wall in the early stage. Znconcentration in the cell wall was significantly higher than that of the vacuole in the late stage.Zn in the normal thin roots was mainly in the cell wall in early stage and in the vacuole in latestage. Zn concentration in the thick roors was higher than the thin roots. Zn concentration ofthe cell wall was higher than the vacuole in rosette roots annually.(4) The subcellular fraction of Zn-containing tissues in Malus hupehensis Rehd showedZn mainly located in the cell wall and least in the vacuole. In Malus xiaojinensis, most of Znwas isolated in the cell wall and the vacuole of roots and stems. However, in Malusxiaojinensis leaves, Zn was mostly located in the vacuole. The chemical forms results showedthat the NaCl-extractable Zn and the distilled water-extractable Zn were the most in Malushupehensis Rehd aerial parts. But in Malus hupehensis Rehd roots, the NaCl-extractable Znwas the most under Zn deficiency while the HAc-extractable Zn was the most under Zntoxicity. While in Malus xiaojinensis, the HAc-extractable Zn was the main Zn form, and theethanol-extractable Zn and distilled water-extractable Zn were the second main Zn forms.(5) The malate and oxalate concentration achieved the highest level in the first day oftreatment in Malus hupehensis Rehd under different Zn deficiency stress. The malate andoxalate were negatively related to Zn, and significantly positive correlation between oxalateand malate. Applying organic acid was significantly increased Zn concentration in roots, notchanged significantly in aerial parts and the highest concentration of Zn was in roots whenorganic acid and Zn molar ratio of1:2. Applying organic acid significantly enhanced organicacid concentration and Zn subcellular distribution in every organ. But the effect to everyorgan of organic acid concentration and Zn concentration was different.