Components of antioxidative system in Allium cepa as the toxicity monitor of trichloroethylene (TCE)

Abstract

Trichloroethylene (TCE) is a potent hepatocarcinogen (National Cancer Institute, USA) and is widely used as a metal degreasing agent. Concentration-dependent effect of TCE exposure on Allium cepa (onion) bulbs for 48 h was determined on the activities of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), glutathione-S-transferase (GST), glutathione peroxidase (GPx), ascorbate peroxidase (APx), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR). Levels of hydrogen peroxide (H2O2), ascorbate (ASC), and glutathione (GSH) were also measured in onion homogenates to monitor TCE-induced oxidative stress. At 200 ppm TCE concentration, the activities of GST and GR in exposed onion bulbs exhibited roughly three-fold induction compared with control, whereas reduction in activities at higher levels of TCE concentration was recorded. A two-fold induction of CAT with a simultaneous and significant induction in activities of APx, GPx, and MDHAR at increasing TCE concentrations was observed at 150 ppm of TCE exposure. Minimum level of induction was observed for SOD (79%) and DHAR (63%) at 250 and 300 ppm of TCE, respectively. Results indicate that GST, GR, APx, and CAT in A. cepa system could serve as potential indicators of TCE-induced enzymatic perturbations.