Zinc alleviates cadmium-induced oxidative stress in Ceratophyllum demersum L.: a free floating freshwater macrophyte

The potential mechanism by which Zn antagonizes Cd toxicity was investigated in Ceratophyllum demersum L. (Coontail), a free floating freshwater macrophyte, to understand the interaction between two metals, one a micronutrient and another a toxic metal. C. demersum was treated with 10 μM Cd along with Zn (10, 50, 100 and 200 μM). Treatments with Zn only (10, 50, 100 and 200 μM) were also given to the plant material. Cd uptake was suppressed by Zn and simultaneously, Zn concentration also increased in the plant. Cd-induced strong oxidative stress as indicated by high levels of lipid peroxidation, electrical conductivity and lipoxygenase (LOX, E.C. 1.13.11.12) activity. Zn supplementation efficiently reduced this as observed by the decrease in these parameters. Zn-alone-treated plants, however, did not show any variation in the above parameters. The activity of antioxidant enzymes superoxide dismutase (SOD, E.C. 1.15.1.1), catalase (CAT, E.C. 1.11.1.6), ascorbate peroxidase (APX, E.C. 1.11.1.11) and guaiacol peroxidase (GPX, E.C. 1.11.1.7) showed a very high increase in activity in Cd + Zn-treated plants as compared to Cd- or Zn-alone-treated plants. This indicates the efficient antioxidative and reactive oxygen species scavenging activity by Zn against Cd-induced free radicals and oxidative stress. Plants treated with only Zn concentrations did not show very high Zn uptake or high antioxidant enzyme activity. These results suggest that Zn supplementation proved to be inhibitory for Cd-induced oxidative stress and beneficial for the plant’s survival.