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

Abstract

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.

Keywords: Ammonium; Plasma membrane H(+)-ATPase; Potassium; Proton extrusion; Rice; Root.