Metal micronutrients in xylem sap of iron-deficient barley as affected by plant-borne, microbial, and synthetic metal chelators

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Abstract
A greenhouse experiment was conducted to study the effects of phytosiderophore (PS), deferriferrioxamine B (Desferal), and ethylene diamine tetraacetic acid (EDTA) on the concentrations of copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) in the xylem sap of Fe-deficient barley (Hordeum vulgare L. cv. Minorimugi) plants grown in 1/2-strength modified Hoagland-Arnon nutrientsolution. Iron-deficient plants (14 d after transfer) were treated with 25, µM metal chelators for 3 h after which the xylem sap was collected for 3 h. Treated plants were compared with Fe-sufficient and untreated Fe-deficient plants. The concentration and translocation of PS, Mn, and Zn increased, while those of Fe decreased in xylem sap of the Fe-deficient plants compared to the Fe-sufficient plants. The concentrations of PS, Cu, Fe, Mn, and Zn in the xylem sap of the Fe-deficient plants increased by the application of PS to the nutrient solution. This fact suggested that PS solubilized the metal micronutrients in the root tissues and/or root apoplast and contributed to the loading of the nutrients to the xylem tubes, thereby leading to a higher nutrient absorption from the rhizosphere of Fe-deficient plants. On the other hand, Fe-deficient plants treated with EDTA showed a decrease in the PS, Cu, Fe, Mn, and Zn concentrations in the xylem sap. Application of Desferal to the nutrient solution slightly increased only the Fe concentration in the xylem sap of the Fe-deficient plants. Organic acids in the xylem sap of the Fe-deficient plants were in the order of succinate > malate > citrate based on the concentrations, and did not appear to be related to the translocation of metal micronutrients.