Plasma membrane ATPase and H+ transport activities of microsomal membranes from wheat roots under Ni deficiency conditions as affected by exogenous histidine

Abstract ATPase activity and ATP-dependent H + transport have been analyzed in membrane vesicles isolated from a winter wheat cultivar ( Triticum aestivum cv. Back Cross Rushan) which was exposed to different concentrations of nickel (Ni) and histidine (His). Seedlings were grown in a modified Johnson nutrient solution and then exposed to the uptake solution containing 10 μM Ni to which either 100 μM His or no amino acid was added. Control plants were transplanted to nutrient solutions free of Ni and His. According to our results, using Ni alone or together with His enhanced the activity of plasma membrane (PM) H + -ATPase and resulted in a higher pH gradient across the plasma membrane. The highest initial rate of H + -pumping by PM H + -ATPase also achieved in the Ni alone treatment which was roughly 2.2 times higher than the control treatment. His applied together with Ni to the nutrient solution resulted in higher Ni uptake but lower H + -ATPase activity. Our results suggest that the (PM) H + -ATPase in wheat roots plays an important role in Ni uptake but using His in combination with Ni can moderate the pump activity. Undissociated Ni-His may directely taken up via His transporters which seems to be less dependent on ATPase activity.