Ascorbate and glutathione contents in duckweed, Lemna minor, as biomarkersof the stress generated by copper, folpet and diuron

Glutathione and ascorbate are essential components of the general antioxida tive strategy to overcome oxidative stress due to environmental constraints such as pollution. The variation of glutathione and ascorbate contents in duckweed (Lemna minor) was investigated after a 48 h exposure to copper, di uron and folpet under laboratory conditions in order to determine whether c hanges in their level could serve as suitable and early biomarkers of pollu tion. One could observe that diuron and folpet caused the glutathione level to increase, its redox status remaining unchanged, while copper led to a d epletion of this antioxidant and to an increase in its oxidation rate. When duckweed was contaminated by folpet and the metal, an increase of the asco rbate pool size occurred from concentrations as low as 1 mg l(-1) and 50 mu g l(-1) respectively. While the ascorbate pool became more oxidized becaus e of exposure to copper concentrations less than or equal to 200 mu g l(-1) , folpet caused an increase in its reduction rate. Diuron was responsible f or depletion of ascorbate, the redox status of which remained unchanged. Be cause it is an adaptation to stress and a defence process, the increase in the antioxidant pool size was proposed as a biomarker of exposure to an uns afe environment. Since depletion of antioxidant and an increase in its oxid ation rate weakened cellular defences and indicated a precarious state, the y could constitute early indicators of toxicity. So they were proposed as p otential biomarkers of toxicity. It was concluded that the antioxidant cont ent in duckweed might serve as a useful biomarker for monitoring water qual ity.