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Aims: The mechanisms underlying magnesium (Mg) uptake by plant roots remain to be fully elucidated. In particular, there is little information about the effects of Mg deficiency on Mg uptake activity. A Mg uptake kinetic study is essential for better understanding the Mg uptake system. Methods: We performed a Mg uptake tracer experiment in rice plants using Mg. Results: Mg uptake was mediated by high- and low-affinity transport systems. The K value of the high-affinity transport system was approximately 70 μM under Mg-deficient conditions. The Mg uptake activity was promoted by Mg deficiency, which in turn fell to the basal level after 5- min of Mg resupply. The induced uptake rate was inhibited by ionophore treatment, suggesting that an energy-dependent uptake system is enhanced by Mg deficiency. Conclusions: The Mg uptake changes rapidly with Mg conditions in rice, as revealed by a Mg tracer experiment. This technique is expected to be applicable for Mg uptake analyses, particularly in mutants or other lines. [ABSTRACT FROM AUTHOR]

The time course of Mg uptake and release using intact rice plants and Mg as a tracer is presented. Since there is no conventional Mg tracer available, Mg was produced via Al(α, 3p)Mg reaction using a cyclotron. Using the purified Mg tracer, it was found that the uptake amount of Mg by the rice plants increased linearly during 30 min of application. After Mg treatment for 90 min, the roots were sequentially washed with iced solution for 120 min. Within about 10 min, almost all of the Mg, that was thought to be weakly bound to the apoplast, was washed away. [ABSTRACT FROM AUTHOR]