Chemiluminescent examination of watercress oxidative stress and trophic level assessment of water quality using the mustard beetle

Watercress is an aquatic plant that readily bioaccumulates heavy metals that may be found in contaminated aquatic systems. Toxic effects of contaminants on plant physiological processes cause changes in oxidase enzymatic activity, which can be measured using a luminometer. The luminometer makes use of the luminescent reaction produced when peroxidases break down hydrogen peroxide into water and an oxygen radical. The resulting oxyradical binds to and oxidizes phenolic groups producing measureable luminescence. Watercress plants were collected from the springs on Tennessee State University campus and were used in root exposure experiments to three different concentrations of heavy metals including lead, nickel, copper, and manganese for 24, 48, and 72 hour exposures. In addition, luminescent measurements were performed on plants exposed to E85, an 85% ethanol and 15% gasoline blend, 99% pure ethanol, and gasoline in root exposure experiments. Whole plants were macerated in order to liberate oxidases, and a one gram sample from each treatment was placed in the luminometer. Aquatic exposure to heavy metals and E85 caused an increase in oxidative enzyme production although gasoline and ethanol caused no significant changes in oxidase concentrations. However, in leaf exposure experiments, volatile effects of E85, gasoline, and ethanol caused increases in oxidase production due to plant stress. Fluorometric and morphometric measurements were also conducted as plant stress comparisons to oxidative enzyme analyses. Fluorometric measurements performed on plants stressed with heavy metals revealed no significant increases in oxidative enzymes. Morphometric measurements of root length showed decreased root growth from all metal exposures except lead and increases in root growth at some concentrations of fuels. In addition to examining plant stress, trophic level effects of contaminates were observed through feeding trials using the mustard beetle (Phaedon viridis). Several metals including copper interfere with the myrosinase enzyme system responsible for watercress allelopathic defense. The mustard beetle is a specialist herbivore that has evolved a detection system that is stimulated by the products of the glucosinolate-myrosinase system. Because copper interferes with myrosinase, adult mustard beetles exhibited a statistically significant preference for uncontaminated plants