Differential Responses of Anti-Oxidative Enzymes to Aluminum Stress in Tolerant and Sensitive Soybean Genotypes

Seedlings of two soybean genotypes, BX10 [aluminum (Al)-tolerant] and BD2 (Al-sensitive), were treated with Al to evaluate the relative root growth (RRG), callose content, Al-sensitive zone, lipid peroxidation, and the anti-oxidative enzyme activities by histochemical and biochemical assays. Under Al toxicity, the RRG reduction of BD2 was more significant than that of BX10, while callose content displayed a contrary trend. The 2-5 mm zone of root apex was the main Al-sensitive zone for soybeans. The activities of superoxide dismutase ( SOD), peroxidase ( POD), catalase ( CAT), and ascorbate peroxidase (APX) were found to be higher in the two genotypes under Al toxicity than that of the controls. The SOD, POD, and CAT activities of BX10; however, were significantly lower than those of BD2. These results implied that producing low quantity of ROS may be one aspect of the Al-tolerant mechanism for soybeans, which in turn helps them adapt to Al stress.