Uptake of cesium by rice plants and its accumulation in brown rice

Abstract

Uptake of K and Cs from roots is competitive, because Cs⁺ is absorbed by K transporters. Uptake of Cs by rice is mainly mediated by a high affinity K transporter, OsHAK1, in the roots. Under low soil-K conditions, Cs uptake is higher due to competition between K⁺ and Cs⁺. Increased expression of OsHAK1 in roots under low soil-K conditions also promotes the uptake of Cs. In the aboveground parts of the rice plant, Cs distribution changes dynamically after the heading stage. During the ripening process,cesium is translocated from the leaf blades and accumulates mostly in the uppermost internode. As yet, no Cesium transporters have been reported in the aboveground parts. The proportion of radiocesium accumulated in brown rice to that in the whole aboveground parts increases under low soil-K conditions. Sufficient K application is needed to prevent the accumulation of radiocesium in brown rice by regulating both the uptake from the roots and the rate of accumulation in the brown rice. Changes in available K and radiocesium in the soil should also be considered, because they vary with soil type and plant growth.