Effect of arsenic toxicity on peroxidase, superoxide dismutase activity and total phenol content in alfalfa (Medicago sativa L.)

Arsenic is a non-essential metalloid with high toxicity potential for all organisms such as plants, which can accumulate in the environment naturally or by anthropogenic activities. Arsenic enters food chains and can cause serious risk to human health after absorbing by plants. In different plant species, arsenic causes oxidative stress by stimulating ROS generation. Therefore, this study was conducted in order to assess antioxidant defense response of alfalfa to oxidative stress due to the application of different concentrations of arsenic (0, 10, 15 and 20 ppm). Contents of total phenol and malondialdehyde as lipid peroxidation index, as well as POD, SOD activities of root and shoot in control and treated plants were measured. The results indicated that MDA content increased about 1.14 times in roots in presence of 10 ppm, and 1.50 times in shoots in presence of 10 and 15 ppm of arsenic compared to control (p≤0.05). As well as, in roots POD activity in all treatments and SOD activity in the highest level showed higher values. In shoots, both enzymes showed significantly decreased activity (p≤0.05) in all treatments. Total phenol content increased in all concentrations and the highest increase was shown in treated plants by 20 and 15 ppm of arsenic in shoots and roots, respectively. Regarding acquired results, it can be concluded that alfalfa partially moderated oxidative stress by altering in antioxidant system activity