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 active sodium uptake. We previously revealed that variation in the expression of OsHKT2;1 underlies the variation in sodium accumulation between a low-sodium-accumulating indica cultivar, IR64, and a high-sodium-accumulating japonica cultivar, Koshihikari. In the present study, we evaluated IR64 and its near-isogenic line IR64-K carrying OsHKT2;1 and neighboring genes inherited from Koshihikari for grain yield. 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 the potassium fertilizer. IR64-K also showed a slightly higher grain yield than IR64 when grown in a paddy field without applying the potassium fertilizer. These results suggest that enhanced sodium uptake ability improves the grain yield of rice plants under low-potassium-input conditions.