Aluminum-induced lipid peroxidation and lignin deposition are associated with an increase in H2O2 generation in wheat seedlings

Wheat (Triticum aestivum cv. Kalyansona) seedlings were exposed to 0, 10, 50, and 100 mu M Al in a 250 mu M CaCl2 solution for 24 h at pH 4.5. Root elongation decreased gradually, while the Al content markedly increased with increasing supply of Al in the solution. The generation of H2O2 during Al stress was investigated biochemically and histochemically, as well as other events related to the decomposition of H2O2. After 24 h treatment, root elongation inhibition was detected at all the concentrations of Al. The level of lipid peroxidation at 10 mu M Al after 24 h treatment was similar to that of the control, while a significant increase in lipid peroxidation was detected at 50 and 100 mu M Al. H2O2 generation was higher at 50 and 100 pm Al than that at 10 mu M Al. These results suggest that Al-inducible lipid peroxidation may require excessive yield of H2O2 Time course experiment, with 10 mu M Al indicated that there is a strongly positive correlation between root elongation inhibition and cellular H2O2, yield. There were no significant changes in the activities of catalase (CAT) and ascorbate peroxidase (APX) in roots at 10 mu M Al after 24 h treatment. However, a significant decrease in the activities of CAT and APX and a large increase in the activities of oxalate oxidase (OXO), guaiacol peroxidase (GPX), and coniferyl alcohol peroxidase (CA-POX) as well as lignin deposition were observed at 100 mu M Al. These results suggest the possible involvement of OXO in the production of a large amount of H2O2 under severe Al stress, whereas GPX and CA-POX may be involved in the degradation of H2O2 leading to lignin deposition.