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⁺.