Effect of Glyphosate and Copper on Photosynthetic Activity of Microalga Thalassiosira weissflogii Exposed to Light of Different Intensity

Abstract: The effect of pollutants (herbicide glyphosate and copper ions) on the efficiency of operation of the photosynthetic apparatus was investigated in marine diatom microalga Thalassiosira weissflogii (Grunow) G.A. Fryxell & Hasle 1977 exposed to different light intensities. Two experimental approaches were taken: recording of rapid light curves of fluorescence and assessment of the dynamics of fluorescence parameters during a model diurnal light cycle at different concentrations of pollutant in the medium. Important differences between the influence of copper ions and glyphosate on the efficiency of operation of photosynthetic apparatus of the cells at different light intensities were revealed. At a sublethal concentration, copper weakly affected photosynthetic activity of algal cells and intracellular concentration of chlorophyll а, although their growth was inhibited. Copper ions and light affected algal photosynthetic machinery as two independent agents and their joint action was additive. In the presence of glyphosate, algae became more light sensitive and their light inhibition threshold diminished. Out of all the examined fluorescence parameters, the herbicide more strongly suppressed relative electron transport rate, rETR, which probably depends on a deceleration or termination of plastoquinone synthesis and a decrease in the concentration of carotenoids in the cells. Elevation of herbicide concentration in water, especially in spring and summer when the levels of insolation are high, is fraught with a reduction in algal photosynthetic activity and primary production of reservoirs and may cause changes in species composition of photosynthesizing organisms.