Rice Na+ absorption mediated by OsHKT2;1 affected Cs+ translocation from root to shoot under low K+ environments

137 Cs diffused into the environment due to a nuclear power plant accident has caused serious problems for safe crop production. In plants, Cs + is similar in its ionic form to K + . Cs + is absorbed and transported mainly by the K + transport mechanism. However, the full picture of the genes contributing to Cs + transport and the transport mechanism of rice is still unclear. This study focused on OsHKT2;1, a candidate Cs + transporter under low K + conditions. To verify the ability of OsHKT2;1 to transport Cs + , the OsHKT2;1 mutant ( hkt2;1 ) was grown in a 137 Cs-contaminated paddy field in Fukushima. The 137 Cs concentration in hkt2;1 aboveground was higher than in the wild type (WT), and the K concentration in these samples did not change between WT and hkt2;1 , whereas the Na concentration was lower in hkt2;1 . Uptake experiments with radioactive tracers ( 22 Na + , 43 K + , and 137 Cs + ) in hydroponic systems with different elemental compositions showed a negative correlation between Na + and Cs + accumulation in rice shoot cultivated under low K + conditions. These results indicated that OsHKT2;1 does not directly contribute to Cs + uptake but is an important factor in regulating Cs + translocation by controlling Na + accumulation. This indicates the possibility of controlling rice Cs content by regulating the Na + environment during cultivation.