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

Abstract

Barley (Hordeum vulgare L.) is a typical ammonium ( NH4 + )‐sensitive crop species and exhibits a futile‐ NH4 + 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 NH4 + efflux process of barley roots. Barley plants were cultivated in hydroponic solution with 1.0 mM NH4 + or 1.0 mM nitrate ( NO3 - ) 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 NH4 + efflux from barley roots was analyzed by scanning ion‐selective electrode technique. The results show that root and shoot growth was repressed by NH4 + nutrition when compared to NO3 - nutrition. Plasma membrane H+‐ATPase activity of barley roots under NH4 + nutrition was significantly higher than that under NO3 - nutrition. Methyl‐ammonium (MeA), a non‐metabolizable analog of NH4 + , had no significant effect on PM H+‐ATPase activity. The enhanced PM H+‐ATPase activity by NH4 + 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 NH4 + efflux from barley roots. Taken together, NH4 + nutrition stimulates PM H+‐ATPase activity, and this stimulation is possibly triggered by NH4 + assimilation in barley roots. NH4 + efflux from barley roots is associated with PM H+‐ATPase activity which could provide the driving force for NH4 + efflux. Ammonium efflux might be considered as a disposal strategy in barley roots which prevents NH4 + overloading the root cytoplasm.

Boron modulates the plasma membrane H+‐ATPase activity affecting nutrient uptake of Citrus trees

“…Uptake of inorganic‐N forms (nitrate and ammonium) by roots presented a close relationship with PM H + ‐ATPase activity (Alvarez‐Pizarro et al, 2014; Falhof et al, 2016; Hippler, Mattos Jr., Boaretto, & Williams, 2018; Zhang et al, 2018). Rice plants grown under N starvation exhibited an increment of root PM H + ‐ATPase activity when N was resupplied in a hydroponic condition (Sperandio, Santos, Bucher, Fernandes, & Souza, 2011).…”

“…Gene expression of nitrate transporters (NRTs) is strictly related to PM ATPase isoforms (Hippler, Mattos Jr., et al, 2018; Tavares et al, 2016). Nitrate taken up by such specific NRTs is more dependent on energy provided by the membrane electric potential produced by the PM H + ‐ATPase activity than N‐NH 4 + (Nikolic et al, 2012; Zhang et al, 2018). However, the quantification of the expression of genes encoding NRTs would be necessary to better characterise the induction of nitrate uptake in citrus rootstocks after B supply.…”

“…However, previous work has demonstrated that potassium (K) concentration in citrus trees increased with the increment of B applied to the soil (Mattos Jr. et al, 2017), likely related to the role of K in the maintenance of charge equilibrium in root cells (Shabala, 2017). The PM H + ‐ATPase activity has recently been correlated with K retention (Shabala, 2017), expanding its known role in the plant nutrition, also reported for absorption of nitrogen (N) (Luo et al, 2013; Zhang et al, 2018), phosphorus (P) (Yan, Zhu, Müller, Zörb, & Schubert, 2002) and iron (Fe) (Santi & Schmidt, 2009). Previously, it was found that B deficiency can decrease the vanadate‐sensitive ATPase activities and ATP‐dependent H + pumping in sunflower cells (Ferrol, Belver, Roldán, Rodriguez‐Rosales, & Donaire, 1993) and the expression of H + ‐ATPase in the PM of tobacco roots (Camacho‐Cristóbal & Gonzáles‐Fontes, 2007).…”

Plasma membrane H+-ATPase overexpression increases rice yield via simultaneous enhancement of nutrient uptake and photosynthesis

“…The H + efflux rates from the WT and OSA1 -ox rice roots were measured using the scanning ion-selective electrode technique (SIET System BIO-003A, Younger USA Science and Technology Corp., Applicable Electronics Inc., Science Wares Inc., Falmouth, MA, USA) (Supplementary Fig. 2f ) 15 , 21 . Briefly, seedlings were placed in 50 mL of growth solution with 2 mM NH 4 + for 12 h. Then, the rice roots of 7-day-old plants were washed with deionised water and equilibrated in the measuring solution for 10 min.…”

“…To use NH 4 + as an N source, rice roots require efficient uptake ability and corresponding assimilation capacity for NH 4 + . Conversely, high tissue accumulation of unassimilated NH 4 + is usually negatively correlated with plant growth 14 , 15 . The assimilation of NH 4 + in root cells requires a C skeleton as the substrate for the synthesis of amino acids through the glutamine synthetase (GS)/glutamate synthase (GOGAT) cycle.…”