Effect of Arsenic Toxicity on Chlorophyll Content and Antioxidative Enzymes Activities in Rice Seedlings

Abstract

Aims: Arsenic (As) contamination in rice is at alarming level as majority of rice growing regions in India are As contaminated. Present investigation is designed to study the better understanding of the physiological and biochemical mechanisms in the amount of chlorophyll change and antioxidative enzymes activity under arsenic stress on rice variety IET-4786 (Shatabdi). Study Design: Completely Randomized Design. Place and Duration of Study: The experiment was carried out in the departmental laboratory of Plant Physiology, Bidhan Chandra Krishi Viswavidyalaya (BCKV), Mohanpur, Nadia,West Bengal during the year 2017-18. Methodology: Two classes of inorganic arsenic- As(V) in the form of Sodium arsenate (Na2HAsO4.7H2O, M. W. = 321.01) and As(III) in the form of Sodium arsenite (NaAsO2, M.W. =129.91) were added to the modified Hoagland nutrient solution@ 2.5, 5.0, 7.5, 10.0, 12.5,15.0 mg L-1concentration. After 20 days of treatment, rice seedlings under arsenate/arsenite treatments were analyzed for change in total chlorophyll content and antioxidative enzymes activity such as superoxide dismutase (SOD: EC 1.15.1.1), catalase (CAT: EC 1.11.1.6), ascorbate peroxidase (APX: EC1.11.1.11) and peroxidase (POD: EC 1.11.1.7). Results: A noticeable decrease in total chlorophyll content was observed with arsenic treatments as compared to control. Various antioxidative enzymes showed significant variable response upon exposure to As(III) and As(V). SOD activities increased at low arsenic exposure up to 7.5 mg L-1 but decreased with further increase in arsenic treatments.  APX and POD activities were increased with increase in arsenic concentrations while CAT activity displayed decreasing trend. Conclusion: The results are suggestive of differential metabolism of As(III) and As(V) in rice and could exert harmfulness in the early development stage of rice at inappropriate concentrations.