The effects of silver and arsenic on antioxidant system in Lemna paucicostata: Different effects on glutathione system

Ag+ (AgNO3) and As3+ (As2O3) exposures resulted in dose-dependent decreases in the growth rate of Lemna paucicostata with IC50 values of 0.101±0.004 mg/mL and 0.753±0.127 mg/mL, respectively. Both Ag+ and As3+ caused dose-dependent increases in lipid peroxidation, a key oxidative damage marker. Additionally, Ag+ and As3+ caused increases in some components of antioxidant system, namely, ascorbate content and peroxidase activities such as ascorbate peroxidase, glutathione peroxidase, and guaiacol peroxidase. However, notable differences between Ag+ and As3+ were found in their effects on the glutathione (GSH) system. Ag+ caused significant decreases in the GSH content and activities of glutamate cysteine ligase (GCL) and glutathione reductase (GR), the enzymes involved in the GSH synthesis and redox recycling, respectively. In contrast, As3+ caused increases in the GSH content and GCL activity. Our results suggest that the Ag+-induced decrease in GSH content accompanied by the decreases in its synthesis and redox recycling is a critical component that further predisposes L. paucicostata to Ag+ toxicity.