Figure 6.

A schematic diagram illustrating a possible mechanism linking the Al-induced exudation of malate and changes in the properties of PM in Al-tolerant (ET8) and Al-sensitive (ES8) wheat lines. Exudation of malate via malate-permeable channels is accompanied by the hyperpolarization of zeta potential and the enhancement of H⁺-ATPase activity in Al-tolerant plants. In contrast, in Al-sensitive plants, more negative zeta potential than in Al-tolerant plants attracts more Al³⁺, causing the depolarization of zeta potential and the decrease in the pumping out of H⁺ through the PM. The activation of a malate-permeable channel and the H⁺-ATPase are indicated by arrows of increased thickness in the Al-tolerant plants.