FIGURE 10.

Mg alleviation of Al-induced photoinhibition via increasing IAA content and transport. Under Al stressed condition, (A) application of Mg increases IAA synthesis and transport in cells; (B) the accumulation of protons produced from water-splitting activity of PSII and from the electron transfer via Cyt b₆f cause lumen acidification; (C) IAA promotes, on the one hand, CEF activity and H⁺-dependent ATP synthesis by activating ATP synthase in thylakoid accompanying with H⁺ transfer from lumen to stoma, leading to decrease ΔpH_pmf between lumen and stroma. The increased CEF and decreased ΔpH_pmf help to sustain electron transport from PSII to PSI and NADPH generation, increasing CO₂ fixation under excess Al stress; (D) on the other hand, IAA and Mg increase PM H⁺-ATPase activity, which enhances H⁺ transfer from stoma to cytoplasm, further decreases the ΔpH_pmf between the lumen and stroma, and balances H⁺ between intracellular and extracellular.