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both cases state-transition will occur. Indeed, Wollman and Lemaire (1988), verificd state-transition in Chlamydomonas reinhardtii mutants lacking the proteins Dl and D2 in PSI1. In another study, Finazzi and Forti (2004), verified that state-transition was induccd by nutrient deficiency, also in Chlamydomonas reinhardtii. Finally, there is several scicntific evidences on glyphosate effects on the chlorophyll content in plants (Kitchen et al, 1981; Muńoz-Rueda et al, 1986; Zobiole et al, 2011) and green algae (Wong, 2000). However, it is not well known how exactly glyphosate might interfer with chlorophyll content, either by a perturbation of chlorophyll synthesis or by the formation of reactive oxygen species degrading the photosynthetic pigments. It was also suggested that aminomethylphosphonic acid (AMPA), glyphosate’s main metabolite could play a role in the toxicity of glyphosate toward chlorophyll synthesis (Reddy et al., 2004).

2.8 Conclusion

Increasing the use and application of glyphosate-based herbicides in agricultural fields increases the possibility of runoff and contamination of adjaccnt aquatic ccosystcms. Riśk assessments tools are neccssary to monitor and prcvent the effects of these herbicides on aquatic life and water. quality. Concerning the phytotoxicily of the glyphosate-based herbieide Factor540*°, we have demonstrated that the growth ratę was a very sensitive parameter, showing sensitivity at concentrations below 10 pg I'¹ (EC10), which are in the rangę of environmental concentrations in Canada and United States. The photosystem II energy flux parameters were also sensitive to glyphosate exposure, but the sensitivity varied among species and parameters. This result implies that glyphosate-based herbicides might interfere, not only via the shikimate pathway, but also with the photosynthetic apparatus. The parameter F_V/F_M, which is often use in photosynthetic studies, was the least sensitive parameter to assess glyphosate-based herbicide effects on algae and cyanobacteria. Microcystis sp. and Scenedesmus obliąuus had their growth significantly reduced at a glyphosate concentration of 50 pg l‘^ł, which is inferior to the Canadian standard for the protection of aquatic life (65 pg I'¹) (CCME, 2008) and the following species had EC|₀ values inferior to the Canadian standard: Microcystis aeruginosea (UTCC632 and UTCC299), Scenedesmus obliquus and Chlamydomonas reinhardtii (UTCCI25), for growth and photosynthesis.