REGULATION OF THE PLANT PLASMA-MEMBRANE H+-ATPASE ACTIVITY

The plasma membrane H+-ATPase plays a central role in many vital plant cell functions. This enzyme belongs to the P type family of cationtranslocating pumps and generates the proton-motive force that drives nutrient uptake across the plasma membrane. It also determines the extracellular acidification associated with elongation growth. The activity of the plasma membrane H+-ATPase is rapidly altered after exposure of plant tissues to plant growth factors such as hormones, light and pathogens. However, very little is at present known about the mechanisms that regulate plasma membrane H+-ATPase activity in the intact cell. The identification of an auto-inhibitory domain in the C-terminus of the plant plasma membrane H+-ATPase implies that there are several possible means by which the enzyme could be regulated. The inhibitory interaction between the inhibitory domain and the catalytic site and/or a proton binding site may thus be regulated by a variety of means, such as the binding of effector molecules, phosphorylation, partial proteolysis, or removal of the inhibitory domain at the gene level. In addition, proton pumping across the plasma membrane could be regulated by changes in the transcriptional activity of H+-ATPase genes or by differential expression of pump isoforms varying in their C-terminal domain.