Effects of aluminum stress on antioxidant enzyme activity in root tips of wheat genotypes differing in aluminum tolerance

The time-dependent effects of aluminum (Al) stress on root elongation, aluminum content, superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), malondialdehyde (MDA) and H₂O₂ in the root tips of Al-resistant (Jian-864) and Al-sensitive (Yangmai-5) genotypes of wheat (Triticum aestivum L.) were investigated by using hydroponics. Root elongation of both genotypes was greatly inhibited with the increasing exposure time to 30 μmol·L^-1 AlCl₃, but more inhibition of root elongation was observed in Yangmai-5. Total Al content in root tips increased as time passed by, with total Al content significantly higher in Yangmai-5 than that in Jian-864. The SOD, CAT and APX activities in root tips of both lines increased with increasing exposure time to Al. There was no significant difference in the 3 enzyme activities of both genotypes at 3 h exposure to Al. In contrast, SOD activity in Yanmgai-5 was distinctly higher than that in Jian-864, while CAT and APX activities in Jian- 864 were markedly higher than those in Yangmai-5 after 6 h exposure to Al. There was no remarkable difference in MDA content in both genotypes at 3 h exposure to Al, whereas MDA content in root tips of Yangmai-5 was significantly higher than that of Jian-864 after 6 h exposure to Al. Meanwhile, H2 O2 content was also enhanced with the increasing exposure time to Al treatment, with more accumulation in Yangmai-5. In conclusion, compared with Al-tolerant genotype (Jian-864), SOD activity in root tips of Al-sensitive genotype (Yangmai-5) was much higher and CAT and APX activities were relatively lower. As a result, H₂O₂ was excessively accumulated in Yangmai-5 and then leaded to oxidative stress and severe lipid peroxidation, thereby significantly inhibiting root elongation.