ADAPTATION OF ACTIVE PROTON-PUMPING AND PLASMALEMMA ATPASE ACTIVITY OF CORN ROOTS TO LOW ROOT MEDIUM PH. (VOL 117, PG 311, 1998)

Corn (Zen mays L.) root adaptation to pH 3.5 in comparison with pH 6.0 (control) was investigated in long-term nutrient solution experiments . When pH was gradually reduced, comparable root growth was observed i rrespective of whether the pH was 3.5 or 6.0. After low-pH adaptation, H+ release of corn roots in vivo at pH 5.6 was about 3 times higher t han that of control. Plasmalemma of corn roots was isolated for invest igation in vitro. At optimum assay pH, in comparison with control, the following increases of the various parameters were caused by low-pH t reatment: (a) hydrolytic ATPase activity, (b) V-max and K-m, (c) activ ation energy of H+-ATPase, (d) H+-pumping activity, (e) H+ permeabilit y of plasmalemma, and (f) pH gradient across the membranes of plasmale mma vesicles. In addition, vanadate sensitivity remained unchanged. It is concluded that plasmalemma H+-ATPase contributes significantly to the adaptation of corn roots to low pH. A restricted net H+ release at low pH in vivo may be attributed to the sleeper pH gradient and enhan ced H+ permeability of plasmalemma but not to deactivation of H+-ATPas e. Possible mechanisms responsible for adaptation of plasmalemma HC-AT Pase to low solution pH during plant cultivation are discussed.