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apparcnt amount of absorbed light energy secms higher, per reaction center, and this is caused by an increased amount of inactive RC’s. This is also followed by an increase of the dissipation energy (DIo/RC), which is also higher because there is less active RC’s. This phenomenon occurred in algae and cyanobacteria cel Is after glyphosate-based herbicide exposure, as shown in figurę 2.1, were the parameters ABS/RC and DIo/RC increased, meaning that glyphosate induced the inactivation of reaction centers of PSU. This can also be reflected by the increased amount of energy trapped by PSII, (TRo/RC), sińce there are less activated reaction centers. Indeed, the amount of trapped energy seems higher per RC, but this is caused by less activated RCs (Strasser et al, 2000, Force et al, 2003). However, the increase of the trapped energy (TRo/RC) only occurred in green algae (S. oblicjuus, O. solitaria, C. reinhardtii, C. snowii and A. falcatus) at high glyphosate concentrations (500 and 1000 pg I'¹). The three species of cyanobacteria, as well as the eryptophyte, C. obovata, showed no variation in the amount of trapped energy (TRo/RC), when compared to the contro!. Howcver, the electron transport (ETo/RC) and the amount of energy absorbed by the antenna complex (ABS/RC) were reduced, while the amount of dissipated energy (DIo/RC) was increased, for cyanobacteria. The electron transport ratę (ETq/RC) and maximal PSII quantum yield (F_v/F_m) of C. obovata were not affected by glyphosate-based herbicide. For the other species, the inactivation of reaction centers or the incapacity of reducing Q_A to Q_A', was retlected by a decrease of the electron transport (ETo/RC), sińce the reoxydation of Q_A‘ did not occur, impacting the electron transport beyond Q_A (Strasser et al, 2000, Force et al, 2003). This is supported by the decrease of the maximal F_V/F_M, indicating a decrcased ability of algae and cyanobacteria to use light energy to perform photochemical reactions.

The three most sensitive species where the three cyanobacteria species (A/. aeruginosea [CPCC299, CPCC632] and Microcystis sp.)_y regarding growth and most of the photosynthetic parameters, except for TRo/RC. These results clearly indicate a higher sensitivity of cyanobacteria to Factor540* herbicide compared to the other species studied. Also, it indicates that there are some metabolic differences regarding the effects on PSII capacity between cyanobacteria and green algae when exposed to this glyphosate-based herbicide. The observed differences on energy fluxes of cyanobacteria and the other algae studied may be exp!ained through the differences of PSII structure. The PSII structure in cyanobacteria is slightly different from PSII structure in green algae and superior plants,