Under stress condition, leaf SOD activity increased significantly (1.7-fold) in the treated plants, while activity of the H2O2-decomposing enzyme APX remained unchanged. Compared Ponatinib buy with control plants, activity of MDAR, GR and DHAR enzymes increased significantly in treated plants. MDAR and GR exhibited an approximately 1.8-fold and 1.6-fold increase in their activity, respectively, while more than the 2-fold increase was measured for DHAR under As-treatment. CAT activity, however, declined by 2-fold, while GPX level increased 5-fold over control value under As treatment [Table 1]. DISCUSSION Cell membrane stability is often related to As tolerance in plants, and the conductance measurement of EL from leaf cells is usually used as an indicator of membrane damage in As-treated plants.
 Change in cell membrane integrity is closely linked with extensive membrane lipid peroxidation in plants.[41,42,43] There is significant evidence that exposure to inorganic As species results in the generation of ROS in plants[20,44] through the conversion of arsenate to highly toxic arsenite within plants. ROS, namely superoxide radicals induce the degradation of phospholipids and the resulting polyunsaturated fatty acids released by such a breakdown are then peroxidised. In the present investigation, marginal increase in tissue MDA content under As exposure indicated non-significant change in rate of lipid peroxidation. Presumably, this helped the plant to maintain membrane integrity as evidenced from the percentage of EL in the treated plant as per control level.
However, higher level of membrane lipid peroxidation and subsequent leakage due to heavy metal-induced generation of ROS was reported in leaves of several common medicinal plants.[12,47] Metal loading of herbal plant parts is of great concern as it can alter the potency of medicinal plants.[47,48] Regulation of cellular redox state is a crucial factor when a plant experiences As-induced oxidative stress. The production of different classes of ROS including H2O2 under different environmental stresses triggers the synthesis of enzymatic antioxidants within the plant cells.[42,43,45] In the present study, increased SOD activity helped the Wedelia plant to quench superoxide radicals under As treatment. However, as has frequently been pointed out, that activity of SOD converts one ROS to another ROS (H2O2).
H2O2 is a predominant oxidant within cell, and its over-accumulation cannot be allowed in an environment where thiol-regulated enzymes Drug_discovery are functioning.[31,33,43] Increased SOD activity coupled with the unchanged level of APX activity and low CAT level might be responsible for higher accumulation of H2O2 in leaves of As-treated Wedelia plants than control plants. Although a positive correlation was usually found between H2O2 accumulation and lipid peroxidation as an obvious indication of oxidative stress, no such relationship was evidenced in the present study.