P-type H⁺ ATPases mediate active H⁺ efflux from plant cells. They generate a proton motive force across the plasma membrane, providing the free energy to drive the transport of other solutes, partly by coupling to H+ influx. Wegner & Shabala (2020) recently suggested that passive H⁺ influx can exceed pump-driven efflux due to ‘active buffering’, that is, cytosolic H⁺ scavenging and apoplastic H⁺ generation by metabolism (‘biochemical pH clamp’). Charge balance is provided by K⁺ efflux or anion influx. Here, this hypothesis is extended to net H⁺ efflux: even though H⁺ pumping is faster than backflow via symporters and antiporters, a progressive increase in the transmembrane pH gradient is avoided. Cytosolic H⁺ release is associated with bicarbonate formation from CO₂. Bicarbonate serves as substrate for the PEPCase, catalyzing the reaction from phosphoenolpyruvate to oxaloacetate, which is subsequently reduced to malate. Organic anions such as malate and citrate are released across the plasma membrane and are (partly) protonated in the apoplast, thus limiting pump-induced acidification. Moreover, a ‘biophysical pH clamp’ is introduced, that is, adjustment of apoplastic/cytosolic pH involving net H⁺ fluxes across the plasma membrane, while the gradient between compartments is maintained. The clamps are not mutually exclusive but are likely to coexist.

Item Type:	Refereed Article
Keywords:	pH clamp, plasma membrane, H+ ATPase pump
Research Division:	Biological Sciences
Research Group:	Plant biology
Research Field:	Plant physiology
Objective Division:	Plant Production and Plant Primary Products
Objective Group:	Other plant production and plant primary products
Objective Field:	Other plant production and plant primary products not elsewhere classified
UTAS Author:	Shabala, S (Professor Sergey Shabala)
ID Code:	147845
Year Published:	2021
Web of Science® Times Cited:	14
Deposited By:	Agriculture and Food Systems
Deposited On:	2021-11-18
Last Modified:	2022-04-08
Downloads:	0