Effects of improved sodium uptake ability on grain yields of rice plants under low potassium supply

Sodium uptake is a factor that determines potassium use efficiency in plants as sodium can partially replace potassium in plant cells. Rice ( Oryza sativa ) roots usually exclude sodium but actively take it up when the plant is deficient in potassium. In rice roots, a sodium transporter OsHKT2;1 mediates the active sodium uptake. We previously revealed that variation in the expression of OsHKT2;1 underlie the variation in sodium uptake between a low-sodium-uptake indica cultivar, IR64, and a high-sodium-uptake japonica cultivar, Koshihikari. In the present study, we evaluated IR64 and its near-isogenic line IR64-K that carrying OsHKT2;1 and neighboring genes inherited from Koshihikari for grain yields. IR64-K had a greater average grain yield and harvest index than IR64 in a pot culture experiment with three levels of potassium fertilizer. The differences were most significant under treatment without potassium fertilizer. IR64-K also showed a slightly higher grain yield than IR64 when grown in a paddy field without potassium fertilizer application. These results suggest that the enhanced ability of sodium uptake improves grain yields of rice plants under low-potassium-input conditions.