Involvement of plasma membrane H+‐ATPase in the ammonium‐nutrition response of barley roots

Abstract

AbstractBarley (Hordeum vulgare L.) is a typical ammonium ()‐sensitive crop species and exhibits a futile‐ efflux from root cells. Plasma membrane (PM) H+‐ATPase is responsible for pumping H+ out of plant cells and providing the driving force for the transport of various substances. We hypothesized that PM H+‐ATPase is involved in this efflux process of barley roots. Barley plants were cultivated in hydroponic solution with 1.0 mM or 1.0 mM nitrate () as the sole nitrogen source. Plasma membrane vesicles were isolated from the root tips for analyses of the activity. Plasma membrane H+‐ATPase was tested by Western Blot. The transcription of PM H+‐ATPase genes was analyzed using qRT‐PCR. Proton and efflux from barley roots was analyzed by scanning ion‐selective electrode technique. The results show that root and shoot growth was repressed by nutrition when compared to nutrition. Plasma membrane H+‐ATPase activity of barley roots under nutrition was significantly higher than that under nutrition. Methyl‐ammonium (MeA), a non‐metabolizable analog of , had no significant effect on PM H+‐ATPase activity. The enhanced PM H+‐ATPase activity by nutrition was consistent with a higher abundance of PM H+‐ATPase protein and higher transcription levels of six PM H+‐ATPase genes. By using the pharmacological agents vanadate and fusicoccin, a close linkage was observed between H+ efflux and efflux from barley roots. Taken together, nutrition stimulates PM H+‐ATPase activity, and this stimulation is possibly triggered by assimilation in barley roots. efflux from barley roots is associated with PM H+‐ATPase activity which could provide the driving force for efflux. Ammonium efflux might be considered as a disposal strategy in barley roots which prevents overloading the root cytoplasm.