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Glyphosate N-(phosphonomethyl)glycine is a systemie and non-selective herbicide, commercialized in 1974, by Monsanto (Duke et Powieś, 2008). It inhibits the shikimate pathway in plants, by competing with the enzyme 5-enolpyruvoylshikimate 3-phosphate synthase (EPSPS) (EC. 2.5.1.19), leading to the accumulation of the substrate shikimate 3-phosphate in plants chloroplasts and to the inhibition of the biosynthesis of chorismate and its by-products (Dewick, 1998; Fedtke et Duke, 2005; Duke et Powieś, 2008). Despite these effects, glyphosate also interferes with photosynthesis (Zobiole et al., 2010, 2012), by forming complexes with cations which are co-factors of important photosynthetic components: magnesium as a co-factor in chlorophyll synthesis (Zobiole et ul., 2011), manganese and calcium as co-factors of the Mn-cluster (Umena et al., 2011) and iron as an csscntial component of the ferredoxin protein (Raven et al., 2005). Matcos-Naranjo et al. (2009) showed a decrease of the maximum photosystem II (PSII) quantum yield (Fv/F_ln), the operational PSII quantum yield (0_PSii), the net photosynthetic ratę, the stomatal conductance, the intracellular C0₂ concentrations and the photosynthetic pigments concentrations, in the macrophyte Spartina densiflora. Similar results were found in other superior plants, such as GR soybeans (Zobiole et al., 2012), glyphosate sensitive soybeans (Vivancos et al., 2011), glyphosate scnsitive Lolium perenne (Yanniccari et al., 2012) and cogongrass (Imperuta cylindrical L.) (Huang et al., 2012). Concerning non-target aquatic plant species, Clioi et al. (2012) found a decrease of Fv/F,_n for five microalgal species when exposed to glyphosate, with somc interspecific differcnces in terms of glyphosate sensitivity.

The aim of the present study was to evaluate the effect of a glyphosate-based herbicide on several algal and cyanobactcria species, isolatcd from the Choinidre reservoir (Eastem Townships. Qucbec, Canada) or from pure culture, from three taxonomic classes by evaluating the PSII energy fluxes. The maximum quantum cfficiency of PSII (F_vyF_in) and the different PSII energy fluxes (ABS/RC, TR<yRC, DI₍₎/RC and ETo/RC) were cvaluated.

2.5 Materiał and Mcthods

2.5.1 Algal cultures and testing procedurę

Bioassays were performed with algal and cyanobacteria species, from three different taxonomic groups, with strains coming from the Canadian Physiological Culture Center