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 O2 ˙- , 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 [CuCl2 , N, N' -dimethylthiourea (DMTU) and catalase] and NOX inhibitors [ZnCl2 and diphenyleneiodonium (DPI)], while H2 O2 promoted PM H+ -ATPase activity at lower concentrations. Repressing effects of Ca+2 antagonists (La+3 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.