Silver nanoparticles toxicity effect on photosystem II photochemistry of the green algaChlamydomonas reinhardtiitreated in light and dark conditions

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Abstract
The inhibitory effect of silver nanoparticles (AgNPs) on photochemical reactions of photosynthesis was investigated using the green alga model Chlamydomonas reinhardtii. Algal cells were exposed to 1, 5, and 10 µmol L−1 of AgNPs under both light and dark conditions during 6 h. The rapid rise of chlorophyll a fluorescence and the fluorescence imaging system were employed to investigate the alteration of photosystem II (PSII) photochemical reactions and the associated electron transport activity. When algal cells were exposed to 5 and 10 µmol L−1 of AgNPs, our results showed the evidence of a structural deterioration of PSII reaction center, the alteration of the oxygen evolving complex and the inhibition of electron transport activity, which was stronger for AgNPs treatment under light exposure. Under these conditions, there was no activation of regulated photoprotective mechanisms against excess absorbed light-energy by the antenna system of the PSII complex. The highest deteriorating effect on the structural and functional integrity of PSII was observed for algal cells exposed 6 h in light condition to 10 µmol L−1 of AgNPs. Therefore, we provide valuable data in this study permitting to use photosynthetic-based fluorescence parameters for aquatic toxicological risk investigation of polluted water that may contain AgNP suspension.

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