Phytochelatins and antioxidant systems respond differentially during arsenite and arsenate stress in Hydrilla verticillata (L.f.) Royle.

Serious contamination of aquatic systems by arsenic (As) in different parts of the world calls for the development of an in situ cost-effective phytoremediation technology. In the present investigation, plants of Hydrilla verticillata (L.f.) Royle were exposed to various concentrations of arsenate (As(V)) (0-250 microM) and arsenite (AsIII) (0-25 microM) and analyzed for accumulation responses vis-à-vis biochemical changes. Total As accumulation was found to be higher in plants exposed to AsIII (315 microg g(-1) dw at 25 microM) compared to As(V) (205 microg g(-1) dw at 250 microM) after 7 d of treatment. Plants tolerated low concentrations of As(III) and As(V) by detoxifying the metalloid through augmented synthesis of thiols such as phytochelatins and through increased activity of antioxidant enzymes. While As(V) predominantly stimulated antioxidant enzyme activity, As(III) primarily caused enhanced levels of thiols. The maximum amount of As chelated by PCs was found to be about 39% in plants exposed to As(III) (at 10 microM) and 35% in As(V) exposed plants (at 50 microM) after 4 d. Only the respective highest concentrations of As(III) (25 microM) and As(V) (250 microM) proved toxic for normal plant growth after prolonged treatment. Thus, H. verticillata forms a promising candidate for the phytoremediation of As contaminated water.