Zinc protects Ceratophyllum demersum L. (free-floating hydrophyte) against reactive oxygen species induced by cadmium

Evidence for Zn protection against Cd-induced reactive oxygen species in the free-floating hydrophyte Ceratophyllum demersum L. is presented in this paper. Metal treatments of 10 μmol/L Cd, 10 Cd μmol/L supplemented with Zn (10, 50, 100 and 200 μmol/L) and Zn-alone treatments of the same concentrations were used. Using 5,5 dimethyl pyrroline-N-oxide as the spin-probe, electron spin resonance spectra indicated a drastic increase in hydroxyl radicals (OH) in Cd-10 μmol/L treatments, which was closely correlating with the enhanced formation of hydrogen peroxide (H2O2) and generation of superoxide radical (O2−) triggered by the oxidation of NADPH. The supplementation of adding Zn (10–200 μmol/L) to the Cd-10 μmol/L treatments significantly decreased the production of free radicals especially by eliminating the precursors of OH through inhibition of NADPH oxidation. Cd-enhanced ROS production which substantially increased the oxidative products of proteins measured as carbonyls was effectively inhibited by Zn supplementation.