CADMIUM REGULATED NITRATE REDUCTASE-ACTIVITY IN HYDRILLA-VERTICILLATA(1F) ROYLE

The study was conducted to evaluate the suitability of nitrate reducta se activity and the level of some metabolites as an in vivo test syste m for cadmium toxicity in submerged macrophyte Hydrilla verticillata. Cadmium (Cd) concentrations ranging from 0.01-80 mu M affected nitrate reductase activity in a differential way. It had stimulatory effect u p to 1.0 mu M Cd, while higher concentrations inhibited the enzyme act ivity significantly. The protein synthesis inhibitor cycloheximide inh ibited Cd- stimulated nitrate reductase activity during in vivo and in vitro essays. However, the effect of Cd on NR activity under ii? vitr o assay was more pronounced. Although low Cd exposures had no effect, higher metal exposures augmented nitrate uptake. This Cd-induced NO3- uptake did not result in recovery of inhibited enzyme activity in vivo . It appears that nitrate reductase activity is more sensitive to Cd t oxicity than the eventual products of nitrate assimilation such as tot al organic nitrogen and soluble proteins. There was a differential res ponse of chlorophyll levels to Cd; lower concentrations enhanced the p igment level while higher ones reduced it. Cadmium exposure always enh anced the levels of carotenoids. Results showed that nitrate reductase activity could serve as an useful bioassay for Cd contamination using H. verticillata.