Abstract
The objective of this study was to investigate the effect of IAA on Al distribution in plant and cell and its mechanism in alfalfa. Seedlings of two alfalfa varieties, WL525 (Al-resistant) and WL440 (Al-sensitive), were exposed to 0 (−Al) or 100μML−1 AlCl3, and were foliar sprayed with water or 6mgL−1 IAA during 3-d treatment. The results showed that Al contents in shoots, root tips and cell wall (CW) were significantly lower in WL525 than in WL440. WL440 had higher Al accumulation in HC1, and WL525 had higher Al accumulation in pectin compared to each other. Exogenous application of IAA significantly reduced Al contents in root tips, CW and pectin fractions, and decreased pectin methylesterase activity (PME) and Al3+ adsorption under Al3+ condition. In addition, exogenous application of IAA alleviated the Al3+-induced damage of cell structure and arrangement in root tips, increased plasma membrane H+-ATPase activity and acidification of rhizosphere. These results indicate that IAA-induced reduction of Al accumulation in cell wall can be associated with decreases in Al3+ binding ability in pectin by increasing H+ secretion to rhizosphere and balancing H+ level between internal and external cells.
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