Magnesium uptake characteristics in Arabidopsis revealed by Mg tracer studies.

The Mg uptake system in Arabidopsis roots is Gd- and Fe-sensitive, and responds to a changing Mg concentration within 1 h with the participation of AtMRS2 transporters. Magnesium (Mg) absorption and the mechanism regulating its activity have not been clarified yet. To address these issues, it is necessary to reveal the characteristics of Mg uptake in roots. Therefore, we first investigated the Mg uptake characteristics in roots of 1-week-old Arabidopsis plants using Mg. The Mg uptake system in roots was up-regulated within 1 h in response to the low Mg condition. This induction was inhibited in Arabidopsis "mitochondrial RNA splicing 2/magnesium transport" mutants atmrs2-4/atmgt6 and atmrs2-7/atmgt7, while the expression of AtMRS2-4/AtMGT6 and AtMRS2-7/AtMGT7 genes in the Arabidopsis wild-type was not responsive to Mg conditions. In addition, the Mg deficiency-induced Mg uptake system was shut-down within 5 min when Mg was resupplied to the environment. An inhibition study showed that the constitutive mechanism functioning in Mg uptake under Mg sufficient conditions was sensitive to a number of divalent and trivalent cations, particularly Gd and Fe, but not to K.