Potassium alleviates ammonium toxicity in rice by reducing its uptake through activation of plasma membrane H+-ATPase to enhance proton extrusion

Potassium (K+) has been reported to alleviate ammonium (NH4+) toxicity in rice through some underlying mechanisms, but it still not clear. In addition, K+ is an important cation for activation of plasma membrane (PM) H+-ATPase activity. Here, we hypothesized that K+ alleviated NH4+ toxicity by mediating PM H+-ATPase function in rice root. In this study, rice plants were cultivated in hydroponic solution with various concentrations of K+ and NH4+. By concurrently supplying K+ with NH4+ or re-supplying K+ after NH4+ toxicity, we found that high K+ concentration reduced the NH4+ uptake rate, enhanced the H+ extrusion rate by the roots, and alleviated rice NH4+ toxicity. The gene expression levels of PM H+-ATPase members (OsA1, 3, 7, 8, and 9) were upregulated by application of increasing concentrations of K+ under NH4+ toxicity. The PM H+-ATPase activity and protein expression in rice roots were also enhanced. Furthermore, the enhancement of PM H+-ATPase activity by a specific stimulator (fusicoccin) rescued rice seedlings from NH4+ toxicity. Taken together, these results indicate that K+ can alleviate NH4+ toxicity, possibly by activating PM H+-ATPase to extrude more H+ and inhibit NH4+ uptake by root. Our results may enhance understanding of the strategy of applying K+ fertilizer to mitigate crop NH4+ toxicity in agriculture.