Calcium regulates K+/Na+ homeostasis in rice (Oryza sativa L.) under saline conditions

Abstract

To investigate the effects of Ca2+ on cation accumulation and K+/Na+ selectivity, in this study, two-week-old rice (Oryza sativa L.) plants were exposed to 25 or 125 mmol/L NaCl with or without 10 mmol/L CaCl2. At low salinity (25 mmol/L NaCl), Ca2+ significantly decreased Na+ accumulation in roots, increased K+ accumulation in shoots, and maintained higher K+/Na+ ratios in both roots and shoots of rice plants. At high salinity (125 mmol/L NaCl), however, Ca2+ did not have any effects on Na+, K+ accumulation and K+/Na+ ratios in plants. Further analysis showed that, at low salinity, the addition of Ca2+ significantly enhanced the selective absorption and transport capacity for K+ over Na+ in rice. Although Na+ efflux and Na+ influx were remarkably reduced by Ca2+ under both low and high salt stresses, their ratio was lowered only under low salt stress. In summary, these results suggest that Ca2+ could regulate K+/Na+ homeostasis in rice at low salinity by enhancing the selectivity for K+ over Na+, reducing the Na+ influx and efflux, and lowering the futile cycling of Na+.