The analysis of magnesium transport system from external solution to xylem in rice root

We report the characterization of magnesium (Mg) transport from external solution to xylem by using xylem fluid analysis in rice (Oryza sativa L. Nipponbare). It was indicated that Mg uptake and/or xylem loading was mediated by two transport systems, a saturable and a linear component. The Km value of the saturable component was approximately 20 mu M, and the saturated concentration was calculated to be 1.5 mM. Using a multi-compartment transport box with excised roots, the transfer from external solution to xylem was shown to be inhibited by hexaamminecobalt(III) {[Co(III)(NH3)6], Co-Hex}, a selective inhibitor of CorA-mediated influx of Mg2+, suggesting that the MRS2/MGT genes that belong to the superfamily of CorA-type membrane proteins are involved in the Mg transport system.