PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

OJIP chlorophyll a fluorescence measurements to assess the effect of pesticide-copper mixtures on duckweed photosynthesis. Philippe EULLAFFROY^*,1, Cécile FRANKART¹, Sylvie BIAGIANTI¹, ¹ University of Reims, Reims cedex 2, France

ABSTRACT- Analysis of the fast chlorophyll fluorescence rise O-J-I-P which reflect the photosystem II photochemistry was carried out to assess toxicity effect of Cu²⁺-diuron, paraquat or flazasulfuron mixtures caused by their interaction. Information about energy absorption, electron transport and further metabolic events were obtained from the same measurement. Lemna minor was exposed to different concentrations of these contaminants during 48 hours. Diuron and paraquat alone caused a decrease in the photosynthetic capacity of duckweed by inhibition of electron transport via photosystem II and I, while copper interacted as a water-splitting inhibitor and flazasulfuron (amino-acid synthesis inhibitor) had only slight effect on photosynthesis. It was also interesting to evaluate the toxicity of these herbicides in combination with copper. Then, it was evident that Cu²⁺ with diuron or flazasulfuron acted in slight synergy on the efficiency of PSII photochemistry and on the fraction of inhibited centres. However, the effect of the Cu²⁺-paraquat mixture seemed to be antagonistic in regard to the same fluorescence parameters. This study demonstrated that OJIP chlorophyll fluorescence kinetics can not only be used to investigate the relationship between photosynthetic electron transport and herbicidal action mechanism but also as a useful physiological tool in detecting contaminant mixture toxicity, such as caused by copper, diuron, paraquat and flazasulfuron, at an early stage.

KEY WORDS: Herbicide, Chlorophyll fluorescence, Duckweed