Congruence between PM H-ATPase and NADPH oxidase during root growth: a necessary probability.

Plasma membrane (PM) H-ATPase and NADPH oxidase (NOX) are two key enzymes responsible for cell wall relaxation during elongation growth through apoplastic acidification and production of ˙OH radical via O˙, respectively. Our experiments revealed a putative feed-forward loop between these enzymes in growing roots of Vigna radiata (L.) Wilczek seedlings. Thus, NOX activity was found to be dependent on proton gradient generated across PM by H-ATPase as evident from pharmacological experiments using carbonyl cyanide m-chlorophenylhydrazone (CCCP; protonophore) and sodium ortho-vanadate (PM H-ATPase inhibitor). Conversely, H-ATPase activity retarded in response to different ROS scavengers [CuCl, N, N' -dimethylthiourea (DMTU) and catalase] and NOX inhibitors [ZnCl and diphenyleneiodonium (DPI)], while HO promoted PM H-ATPase activity at lower concentrations. Repressing effects of Ca antagonists (La and EGTA) on the activity of both the enzymes indicate its possible mediation. Since, unlike animal NOX, the plant versions do not possess proton channel activity, harmonized functioning of PM H-ATPase and NOX appears to be justified. Plasma membrane NADPH oxidase and H-ATPase are functionally synchronized and they work cooperatively to maintain the membrane electrical balance while mediating plant cell growth through wall relaxation.