Chemiosmotic circuits of plant cells are driven by proton

(H+) gradients that mediate secondary active transport of

compounds across plasma and endosomal membranes. Furthermore,

regulation of endosomal acidification is critical for endocytic

and secretory pathways. For plants to react to their

constantly changing environments and at the same time maintain

optimal metabolic conditions, the expression, activity and interplay

of the pumps generating these H+ gradients have to be

tightly regulated. In this review, we will highlight results on the

regulation, localization and physiological roles of these H+-

pumps, namely the plasma membrane H+-ATPase, the vacuolar

H+-ATPase and the vacuolar H+-PPase.

2007 Federation of European Biochemical Societies. Published

by Elsevier B.V. All rights reserved.