Effects of cycloxydim on population growth, phagocytosis, contractile vacuole activity and antioxidant responses in the freshwater ciliate (Paramecium tetraurelia)

Abstract

The continuous contamination of the aquatic environments by numerous agricultural and industrial pollutants has triggered the need to identifying new models and bioassays for assessing water pollution and understanding toxic effects of these xenobiotics at different levels. In the present study, investigation was done on physiological changes and antioxidant responses of the freshwater ciliateParamecium tetraurelia exposed to a selective herbicide; Focus Ultra (a.i., cycloxydim: 100 g L–1). Our results revealed an inhibitory effect on the cell proliferation rate. The growth inhibitory concentration (IC50) was found to be 7.53 mg L–1. Thus, the number and the velocity of generation were decreased when the generation time was extended significantly at the higher concentration of Focus Ultra (12 mg L–1). The normal functioning of the contractile vacuole was also significantly affected at this concentration. Focus Ultra caused evenly a dose dependent stimulation of the phagocytic activity. Furthermore, monitoring biomarkers of oxidative stress showed a significant depletion in glutathione level (GSH) accompanied with a strong increase of glutathione S-transferase (GST) and catalase (CAT) activities reflecting the toxic effects of this herbicide on Paramecium tetraurelia cells.