Aluminum-induced plasma membrane surface potential and H+-ATPase activity in near-isogenic wheat lines differing in tolerance to aluminum

This study aims to clarify the effect of aluminum (Al) on the surface potential and the plasma membrane (PM) H+-ATPase activity, as linked to exudation of organic acid anions, using near-isogenic Al-tolerant (ET8) and Al-sensitive (ES8) wheat (Triticum aestivum) lines. We examined the surface potential (zeta potential) and H+-ATPase activity of PM vesicles obtained from the root tips (10 mm) and the region distal to the root tip of wheat treated with Al either in vivo or in vitro. After 4-h in vivo treatment with Al (2.6 mum), H+-ATPase activity and H+ transport rate were decreased and zeta potential was depolarized in PM vesicles from root tips of Al-sensitive ES8 but not of Al-tolerant ET8. In vivo treatment with 50 mum malate alleviated deleterious Al effects on H+-ATPase activity and the zeta potential in PM vesicles isolated from root tips of ES8. In PM vesicles from root tips, in vitro treatment with 10 mum Al had a greater inhibitory effect on H+-ATPase activity of ES8 than that of ET8. However, in vitro Al treatment did not influence the H+-ATPase activity in PM vesicles prepared from the region distal to the root tip in the two wheat lines. Al-induced exudation of malate, as a basis for the mechanism of Al tolerance, is accompanied by changes in PM surface potential and the activation of H+-ATPase.