An Assessment of Oxidative Stress and Antioxidant System Activity in Alfalfa Plants Treated with Different Forms of Mineral Arsenic

Arsenic (As), a metalloid and unnecessary element, is highly toxic to living organisms. It can be accumulated in the environment and enter the food chains through uptake by plants. The present study was designed to assess the response of antioxidant defense system of alfalfa to As (As0, As3+ and As5+) induced oxidative stress at four rates (0, 100, 200, and 300 µM) as a completely randomized design with three replications in the laboratory conditions. Tukey test was used for data analysis. The 90-day seedlings after harvesting, were used to evaluate MDA and H2O2 contents, antioxidant system, including SOD, POD, APX, CAT activities, contents of phenol, flavonoids and anthocyanin. According to the results, root and shoot H2O2 contents of As3+-treated plants, were the highest at the rate of 300 µM and the MDA contents were the highest at the rates of 200 and 300 µM in root and shoot, respectively. However, in 200 µM of As0-treated plants, the MDA content showed a significant decline (P≤ 0.05). The antioxidant responses varied with different treatments. Increased free radical scavenging activity was only observed at lower rates of As5+ in the shoot. Consequently it can be concluded that all of three forms of As, induced oxidative stress, which As3+ (300 µM) was more toxic than As0 and As5+. Nonetheless, the alfalfa plant mitigated As-induced oxidative stress by manipulating the activity of their antioxidant system through increasing contents of total phenol, flavonoids, anthocyanin and changing antioxidant enzymes activities, in different types and rates of As.