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 (As۰, As۳+ and As۵+) induced oxidative stress at four rates (۰, ۱۰۰, ۲۰۰, and ۳۰۰ µM) as a completely randomized design with three replications in the laboratory conditions. Tukey test was used for data analysis. The ۹۰-day seedlings after harvesting, were used to evaluate MDA and H۲O۲ contents, antioxidant system, including SOD, POD, APX, CAT activities, contents of phenol, flavonoids and anthocyanin. According to the results, root and shoot H۲O۲ contents of As۳+-treated plants, were the highest at the rate of ۳۰۰ µM and the MDA contents were the highest at the rates of ۲۰۰ and ۳۰۰ µM in root and shoot, respectively. However, in ۲۰۰ µM of As۰-treated plants, the MDA content showed a significant decline (P≤ ۰.۰۵). The antioxidant responses varied with different treatments. Increased free radical scavenging activity was only observed at lower rates of As۵+ in the shoot. Consequently it can be concluded that all of three forms of As, induced oxidative stress, which As۳+ (۳۰۰ µM) was more toxic than As۰ and As۵+. 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.

Keywords:

oxidative stress , arsenic , enzymatic antioxidant , non-enzymatic antioxidant , Medicago sativa.