Inhibitory effect of Ca added to the medium on Cs absorption by plants

Accidents at nuclear facilities result in the release of radiocaesium (¹³⁷Cs) into the environment. Therefore, a major challenge is to assess and reduce the internal exposure derived from the crops grown in contaminated soil. To solve this problem, we have developed a method to inhibit ¹³⁷Cs absorption by supplying calcium (Ca) to plant roots. At potassium concentrations above 100 μM, Cs absorption is mainly mediated through voltage insensitive cation channels (VICCs). the transport activity of VICCs is inhibited by Ca at millimolar concentrations. Therefore, we hypothesized that Ca might effectively inhibit ¹³⁷Cs absorption. We grew Arabidopsis thaliana on a medium containing 0.1 mM stable Cs and 0.5-3 mM Ca, and measured the concentration of stable Cs in the plants using inductively coupled plasma mass spectrometry. Rice (Oryza sativa) were then grown in a culture medium containing 0.01 μM stable Cs and 0.2-10 mM Ca, and the cesium concentration at the shoots was measured as in Arabidopsis. The results showed that the stable Cs concentration in both plants decreased with increasing Ca concentration in the medium. Similar results were also obtained in an experiment in which Arabidopsis was grown in the presence of 150 Bq of ¹³⁷Cs and 3 or 10 mM Ca. This suggests that Ca has an inhibitory effect on the absorption of ¹³⁷Cs. (author)