Abstract: Effects of two wettable copper powders,cuprous oxide(Cu₂O)and cupic hydroxide[Cu(OH)₂)],varying in concentration on activity of antioxidases [superoxide dismutase(SOD),ascorbate (APX),and peroxidase (POD)],content of malondialdehyde(MDA) and content of chlorophyll in leaes of Vallisneria natans were studied.Results show that exposure to Cu₂O W.P.(0.15-1.5 mg·L^-1)for 7 days significantly increased specific activities of superoxide dismutase(SOD),ascorbate peroxidase (APX) and peroxidase (POD) in the leaves of the plant.In the treatment,highest in concentration of the pollutant (1.5 mg·L^-1),sapecific activities of the three anti-oxidative enzymes increased by 49.0%,77.0% and 39.0%,respectively,and content of MDA dramatically increased by 46.9%,but content of total chlorophyll decreased by 42.6%.After the plant was exposed to the toxicant for 14 days,the specific activities of the three anti-oxidative enzymes in the plant receded to a varying extent,the content of MDA returned to its normal level,and the content of chlorophyll somewhat recovered.When exposed to Cu(OH)₂ W.P.(01.-1.0 mg·L^-1 )for 7 days,the plant in the treatment highest in concentration (1.0  mg·L^-1)of the toxicant showed a similar trend in specific activities of anti-oxidative enzymes,MDA level and chlorophyll content.And when the exposure lasted for 14 days,the activities of anti-oxidative enzymes and the MDA level fell back to their normal ranges,and the content of total chlorphyll also went up.The above-listed findings indicate that at the early stage of the cupper stress caused by cuprous oxide and cupic hydroxide,activities of the anti-oxidative enzymes in Vallisneria natans ascend in respingse to oxidative stress,causing certain oxidative damage to membrane lipid and decline of chlorophyll content.But with duration of the exposure extending,the plant gradually gets adapted to the stress,with oxidative damage mitigated and chlorophyll content recovered.

Key words: cuprous oxide Cu₂O, cupic hydroxide[Cu(OH)₂)], Vallisneria natans, anti-oxidative enzyme, malondialdehyde(MDA), chlorophyll