Physiological study of combined heavy metal stress on Hydrilla verticillata (l.f.) Royle

Evaluation of toxicity of Lead and Cadmium was done by using aquatic plant Hydrilla verticillata at different durations of 3 day and 7 day under combined concentration of metals during summer season. Inhibition of growth of aquatic plant was measured as reduction in fresh biomass due to toxic effect created by metals. Reduction in chlorophyll content, protein and in vivo NR activity was measured when exposed to higher concentration i.e. 20.0 ppm Pb + 5.0 ppm Cd for 3 day but reduction was more evident during 7 day exposure whereas increase in carotenoid and proline content was observed with increase in combined metal concentration for both 3 day and 7 day durations. Study showed that higher combined metal concentration caused toxic effect which was duration dependent also.