Antioxidative Response of Hydrilla verticillata (L.f.) Royle under Short Term Exposure to Mercuric Chloride

Hydrilla verticillata (L.f.) Royle twigs were subjected to HgCl2 (10, 50, 100 and 200 mg/L) for 3 h under light and dark conditions. There was significant loss in total chlorophyll, soluble protein and ascorbic acid contents in the twigs with increased Hg concentrations in the medium. Superoxide dismutase (SOD) activity increased in a concentration dependant manner indicating the increased protection against superoxide radical under Hg stress but at the same time the generation of higher amount of H2O2 as dismutation product was also favoured. At lower concentration, there was increase in catalase (CAT) activity but it declined significantly towards higher concentrations of Hg as a result the protection against H2O2weakened. Even though there was increase in peroxidase (POX) activity, it could not be attributed to efficient H2O2 scavenging. Malondialdehyde (MDA) content in the tissues increased which suggested that there was imposition of oxidative stress due to Hg. The addition of antioxidant (ascorbate) to the medium reduced the toxic effects. The results suggest that the Hg induced oxidative stress was probably due to alterations in the activities of key antioxidative enzymes viz SOD, CAT and POX. Therefore, increased antioxidant efficiency could increase the tolerance of the plant to the metal and thereby it could be a better candidate for Hg bioaccumulation in polluted water bodies.