Photosynthetic responses of Lemna minor exposed to xenobiotics, copper, and their combinations.

The effects on the photosynthetic process of copper and pesticides, used in vineyards, and their combinations, were investigated by measuring different chlorophyll fluorescence parameters in Lemna minor. Cu and flumioxazin had a severe impact on duckweed since a decrease in their photosynthetic capacity was detected after 24h of exposure to 200 and 1 microg.L(-1), respectively. However, fungicides used to control Botrytis cinerea (procymidone, pyrimethanil, and fludioxonil) seem to have no marked effects on duckweed even at very high concentrations (50 mg.L(-1)). Analysis of the combinations between copper (200 microg.L(-1)) and pesticides revealed different patterns of response: a synergistic effect was observed when Cu(2+) was added to flumioxazin (1 microg.L(-1)). In contrast, an antagonism was detected when duckweed was exposed to a mixture of Cu(2+) and fludioxonil or procymidone. However, these interactions always tended toward additivity when pesticide concentrations increased. Additivity was also observed for the Cu(2+)-pyrimethanil mixture at each fungicide concentration.