Rhizosphere pH difference regulated by plasma membrane H+-ATPase is related to differential Al tolerance of two wheat cultivars

Aluminum (Al)-tolerance of different cultivars shows considerable differences. Elevation of rhizosphere pH is an external Al-resistant mechanism of plants. To elucidate the correlation between Al tolerance and the capacity of plants to modify the rhizosphere pH at different Al-tolerant levels, a comparative study on the wheat (Triticum aestivum L.) cultivars ET8 (Al-tolerant) and ES8 (Al-sensitive) was performed. Rhizosphere pH of ET8 was much higher than that of ES8 under the same treatment, significant correlations were obtained among all the data of rhizosphere pH and relative root elongation (R2 = 0.9209**), or Al content in root apex (R2 = 0.9321**), which indicated that Al tolerance may be related to pH changes in the rhizosphere. The elevation of rhizosphere pH was inhibited by H+-ATPase specific inhibitor DCCD (dicylcohexylcarbodiimide, 25 mmol). Relative PM (plasma membrane) H+-ATPase activity of ET8 was significantly higher than that of ES8 under the same treatment. Significant correlation between all the data of relative PM H+-ATPase activity and rhizosphere pH (R2 = 0.8319**) were obtained. Taken together, these results suggest that PM H+-ATPase was involved in regulating rhizosphere pH. Under Al stress, the Al-tolerant line showed a stronger capacity of up-regulating rhizosphere pH by PM H+-ATPase than the Al-sensitive line, which may explain the observed differences in Al tolerance between the two wheat cultivars.