Effect of oxyfluorfen and diuron alone and in mixture on antioxidative enzymes of Scenedesmus obliquus

Oxyfluorfen and diuron, herbicides commonly used in champagne vineyards, are known to generate reactive oxygen species (ROS) which induce a shift of the balance between prooxidative and antioxidative reactions. Against this oxidative stress, plants have developed enzymatic defenses such as superoxide dismutase, peroxidases, and catalase to limit lipid peroxidation, DNA damage, and protein degradation. These antioxidative enzyme activities were used as biomarkers in the present study to evaluate the toxic effect of oxyfluorfen and diuron on the microalgae Scenedesmus obliquus. Enzymatic activities were measured in the presence of these compounds alone and in mixture after a 24-h exposure to analyze the interactions between these herbicides. Catalase, ascorbate peroxidase, glutathione reductase, and glutathione S-transferase activities were investigated after the exposure of the microalgae to herbicide concentrations responsible for 25, 50, and 75% of growth inhibition. Antioxidative enzymes were significantly stimulated by oxyfluorfen, while no significant variation of catalase and ascorbate peroxidase activity was observed with diuron. However, this herbicide stimulated glutathione reductase and glutathione S-transferase of Scenedesmus obliquus. Growth inhibition test with oxyfluorfen and diuron in mixture showed an antagonistic interaction. At the enzyme level, antagonism was observed only with catalase. According to our data, diuron effect was not caused by an increased stimulation of algal antioxidative enzymes by the photosystem II herbicide.