Increased PM H⁺-ATPase activity induces the Al hypersensitivity of sal1. A, B) Effect of vanadate (VA) A) or FC B) supply on Al resistance during the first and/or second 24-h treatment. Five-day-old seedlings of WT and sal1 were exposed to a 0.5 mM CaCl₂ solution (pH 4.5) containing 0 or 20 µM Al and with or without 250 µM Na₃VO₄ or 1 µM FC for 24 and/or 48 h, and root elongation was calculated for the evaluation of Al resistance. C, D) Knockdown of OSA7 by RNAi rescues the Al-hypersensitive phenotype of sal1. C) Decreased expression of OSA7 in three OSA7-RNAi lines with sal1 background. D) Comparison of Al-resistance phenotype in WT, sal1, and three OSA7-RNAi lines with sal1 background. E, F) Overexpression of OSA7 increases Al sensitivity. Scale bar = 2 cm. E) Increased expression of OSA7 in three pZmUBQ:OSA7 overexpression lines with WT background. F) Comparison of Al-resistance phenotype in WT, sal1, and three OSA7 overexpression lines. Geminated seeds were exposed to a 0.5 mM CaCl₂ solution (pH 4.5) containing 0 or 20 µM Al for 5 d, and the root length was measured for the evaluation of Al resistance. Scale bar = 2 cm. Values are means ± SD of 10 (A, B, D, and F) or 3 (C and E) biological replicates. In all bar graphs of this figure, means with different letters are significantly different (P < 0.05, analysis of variance test followed by Tukey's test).