Assessment of cobalt accumulation effect on growth and antioxidant responses in aquatic macrophyte Hydrilla verticillata (L.f.) Royle

Cobalt is an essential trace metal and plays a pivotal role in the growth of all living organisms. The exposure of cobalt in the aquatic environment is ubiquitous via both natural and anthropogenic activities. The present study was carried out to investigate the accumulation response of macrophyte Hydrilla verticillata (L.f.) Royle towards the cobalt exposure at different concentrations (1, 25, 50, 75 and 100 µM) for seven days. The results showed that the cobalt accumulation increased in treated H. verticillata (L.f.) Royle with increase in concentration. The Bioconcentration factor (BCF) values were high in plants exposed to higher concentration of cobalt. Increase in growth (shoot length) and pigments (chlorophyll a, b and total chlorophyll) were detected at 25 µM cobalt concentration, whereas the growth and pigments were declined in 50, 75 and 100 µM. There was no significant difference in the carotenoid content between control and treated plant. Antioxidant enzymes (superoxide dismutase, catalase, and peroxidase) were increased at higher concentrations of cobalt. The results indicated that the decline in growth and pigments, and an increase in antioxidant enzyme activities, were triggered by the accumulation of cobalt in the plant. These observations suggest that H. verticillata (L.f.) Royle is well equipped to accumulate low concentration of cobalt in tissues to increase its growth and detoxify ROS generation. The BCF results indicate the efficiency of using H. verticillata (L.f.) Royle as a phytostabilizer.