chlorophyll-a and dichlorprop

The effect of heavy metal toxicity on the environment is usually linked to changes in the glutathione redox cycle and oxidative damage as causative events. However, it is unknown whether changes in the glutathione redox cycle are a cause or result of Cu(II) toxicity. Herein, a new chiral perturbation strategy involving a chiral herbicide, dichlorprop (DCPP), as a perturbation factor was used. According to the dose-response fitting curve of DCPP and the combination with Cu(II), 40 μM (R)-DCPP and (S)-DCPP, whose toxicities were low enough to not significantly perturb the Cu(II) toxicity, were selected as the chiral perturbation factor. When Scenedesmus obliquus was incubated with the chiral perturbation factor and 10 μM Cu(II), chiral perturbation was observed in the chlorophyll content and the PAM chlorophyll fluorescence. Then, the role of the glutathione redox cycle in the toxicity of Cu(II) was evaluated with the chiral perturbation approach. The results revealed that the GSH differences in algae cells exposed to (R)-DCPP or (S)-DCPP were well correlated with the differences in the production of reactive oxygen species (ROS) after exposure to the two enantiomers. When (R)-DCPP or (S)-DCPP was added with Cu(II) to the algae culture, treatment with (R)-DCPP-Cu resulted in a decrease in the GSH content in algae cells compared to the control, whereas treatment with (S)-DCPP-Cu resulted in an increase in the GSH. The GSH/GSSG ratio and GR activity also showed similar enantioselectivities. The enantioselectivities would not exist if the changes of in glutathione redox cycle were the cause. Therefore, these data provide indirect evidence that ROS induced cell toxicity of Cu is a causative event, which results in the response of the glutathione redox cycle. These results also provided an implication that before sustainable detoxification strategies for heavy metal pollutants were proposed, it is better that the roles of ROS production and glutathione redox cycle are elucidated. In this case, the chiral perturbation strategy may be a good choice.

Topics: 2,4-Dichlorophenoxyacetic Acid; Chlorophyll; Copper; Environmental Monitoring; Glutathione; Herbicides; Oxidation-Reduction; Oxidative Stress; Photosynthesis; Reactive Oxygen Species; Scenedesmus; Stereoisomerism; Water Pollutants, Chemical

Reactive oxygen species (ROS) are considered to be the key players in cell toxicity. However, cross talk between the enantioselective toxicity of pesticides, heavy metals, and ROS is poorly understood. To decipher the puzzle, the effects of copper (Cu) on the enantioselective ecotoxicity of the chiral pesticide dichlorprop (DCPP) to Scenedesmus obliquus were investigated. The results showed that the presence of DCPP and Cu, both individually and in combination, caused a sudden increase of ROS. This in turn stimulated the response of antioxidant defenses, impaired subcellular structure and physiological function, and finally resulted in cell growth inhibition. In the absence of Cu, ROS production after exposure to the herbicidally active (R)-enantiomer was higher than that of the (S)-enantiomer, suggesting a preference for an (R)-enantiomer-induced production of ROS. When DCPP and Cu were both added to algae simultaneously, (R)-DCPP preferentially induced production of ROS was observed. However, the enantioselective induced production of ROS was reversed when DCPP was mixed with Cu for 24 h prior to addition to the algae solution. It was also found that the generation of ROS, antioxidant response, and growth inhibition rate in Scenedesmus obliquus were all (R)-enantiomer preferentially induced. These findings implied that ROS play a primary role in chemical contaminant toxicity, and interactions between contaminants can tune the enantioselectivity of chiral herbicides, which should be considered in future risk assessment.

Topics: 2,4-Dichlorophenoxyacetic Acid; Antioxidants; Cell Membrane Permeability; Chlorophyll; Copper; Herbicides; Malondialdehyde; Oxidative Stress; Pesticide Synergists; Reactive Oxygen Species; Scenedesmus; Stereoisomerism