The Relationship Among Zinc Absorption, Translocation, Distribution And Organic Acids In Apple Tree Under Zinc Stress

Zinc (Zn) is an essential microelement in plants, playing an important role in many biochemical processes. Apple is one of the four major fruits in the world and is sensitive to Zn deficency. Zinc deficiency and Zn toxicity could disorder carbon metabolism of apple tree, which affected the yield and quality of apple. Organic acids are not only intermediate products of carbon metabolism, but also can participate in the absorption and distribution of mineral elements in the form of energy, structure and ligands substance. However, apple tree is characteristic of perennial growth and successive nutritional storage. As the carbon metabolism mechanism is complicated, the problem of how organic acids influence Zn uptake, translocation and distribution in apple tree under Zn stress is unclear currently.'Fuji'of full fruiting period in the field, two-year-old sand cultivar'Fuji'and water cultivar Malus hupehensis (Pamp.) were selected as materials to explore the influence and relationship among Zn uptake, translocation, distribution and organic acids under Zn stress in apple tree. The main results were as follows:1. Zn and organic acids concentrations were mostly higher in root of rosette tree than that of normal tree at budding stage. However, at florescence stage, Zn and organic acids concentrations were mostly higher in root of normal tree than that of rosette tree. At physiological fruit dropping stage, Zn concentration of root was higher in rosette tree than that in normal tree. Organic acids concentrations in thin roots decreased in rosette tree while increased in normal tree, but in thick roots increased in rosette tree while decreased in normal tree. Zn concentrations were significantly correlated with organic acid concentrations at the three stages.2. According to further verification of pot experiment, Zn deficiency significantly increased the contents of oxalic acid, malic acid and tartaric acid in absorbing roots and tartaric acid in extensive roots in two-year-old'Fuji'. High Zn stress increased the tartaric acid content in absorbing roots and decresed the tartaric acid and malic acid content in extensive roots. It illustrated that Zn deficiency and toxicity resulted in root organic acids contents changed in apple tree.3. Short-term Zn deficiency decreased the hydroponical Malus hupehensis (Pamp.) Zn contents of roots and increased tartaric acid, malic acid and oxalic acid concentrations in roots and stems. Zinc concentration in protoplasts of root was not changed. Correlation analysis showed that zinc and organic acid concentrations were significantly negatively related at this time. Zinc deficiency also resulted in organic acids distribution in root increase. With the prolong of growth time, root length and root area increased, root to shoot ratio, root secretion of tartaric acid and malic acid concentrations increased, Zn uptake rate elevated.4. Long-term Zn deficiency stress reduced Zn concentrations in roots, stems and leaves of hydroponical Malus hupehensis (Pamp.), net photosynthetic rate, and internal organic acids decreased. Root length, root area, root diameter and number of tips decreased significantly.5. Under the condition of short-term Zn toxicity stress, the hydroponical Malus hupehensis (Pamp.) roots, stems and leaves of Zn concentrations were significantly increased, tartaric acid and malic acid concentrations in roots, stems and leaves and oxalic acid concentration in roots increased, Zn concentrations in the vacuole and cell wall increased. Correlation analysis showed that organic acid levels were significantly positively correlated with Zn levels, while significantly negatively correlated with Zn transfer factor at this time. At the same time Zn toxicity promoted the organic acids allocation in root, with the prolong of growth time, root length, root area, root to shoot ratio increased, root secretion of malic acid content increased, Zn uptake rate increased, but Zn transfer factor decreased.6. Long-term Zn toxicity stress increased Zn concentrations of each organ in the hydroponical Malus hupehensis (Pamp.), tartaric acid, malic acid and oxalic acid concentrations of roots and leaves decreased, root diameter and number of tips significantly reduced, Zn transfer factor decreased.7. Exogenous organic acids promote the hydroponical Malus hupehensis (Pamp.) Zn absorption and translocation under Zn deficiency and reduced the root accumulation under Zn toxicity.