Paraquat (PQ) is a toxic chemical that is widely used as herbicide in developing countries. This has led to extensive contamination of the environment, foods and food products. Therefore, this study investigated possible occurrence of PQ residues in some commonly consumed vegetables and the mode by which some of them were able to withstand oxidative stress condition associated with PQ toxicity. Levels of PQ residues and constituent antioxidant enzymes activities were determined spectrophotometrically. Paraquat residue concentrations in all vegetables were in the range of 0.04 to 0.27 ppm. A significant (p<0.05) increase in the activities of catalase, peroxidase and superoxide dismutase were observed in PQ-treated Amaranthus caudatus, Celocia argentea and Chorchorus olitorius as compared to the control groups during the first week of growth. Vegetables treated with 0.50 mM PQ showed initial signs of wilting without necrotic lesions. A progressive increase in malondialdehyde (MDA) content of PQ-treated vegetables compared to the control was observed. The chlorophyll content of the treated vegetables decreased with increased PQ concentrations. These results did not only revealed that these vegetables showed differential sensitivity to PQ, but also suggested that elevated antioxidant enzyme activities, especially during early stage of growth, is one of the likely mechanistic basis for the observed tolerance withholding capacity of these vegetables to PQ.
Key words: Paraquat, mode of action, leafy vegetables, antioxidant enzymes.
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