Magnesium deficiency-induced magnesium uptake revealed by radiotracer studies

Ogura T1, Kobayashi NI1, Suzuki H2, Iwata R3, Nakanishi TM1 and Tanoi K1,4

  1. Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
  2. National Institute of Radiological Sciences, National Institutes for Quantum and Radiological Science and Technology, 4-9-1 Anagawa, Inage-ku, Chiba-city, Chiba 263-8555, Japan.
  3. Cyclotron and Radioisotope Center, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8578, Japan.
  4. PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.

It has been hypothesized that plants regulate the membrane transport of Mg2+ to maintain the optimum concentration in cells for growth. However, some studies suggest that gene expression of Mg2+ transporters does not increase in response to low Mg2+condition. To investigate the mechanism of Mg2+ transport, we tried to elucidate whether and how Mg2+ uptake responds to environmental changes. To investigate Mg2+ uptake rate in root, we prepared 1-week-old Arabidopsis plants and performed Mg2+uptake experiments using agarose plates with 28Mg as a radiotracer. The Mg2+ uptake rate in root increased in response to low Mg2+ condition for 24 h, however, this increase was not observed in the Mg2+ transporter mutants atmrs2-4 and atmrs2-7. In addition, AtMRS2-4 and AtMRS2-7 gene expression in wild-type Arabidopsis did not increase in low Mg2+ condition. In wild-type Arabidopsis, Mg2+ uptake rate increased within 30 minutes at earliest. The low-Mg2+-induced increase was repressed within 5 minutes when Mg2+ was resupplied. An additional experiment to investigate Mg2+ uptake inhibition with other cations under Mg2+sufficient condition showed that the Mg2+ uptake system was sensitive to a number of divalent and trivalent cations, but not to K+.