Inhibitory effects of silver nanoparticles on photosystem II performance in Lemna gibba probed by chlorophyll fluorescence

Toxic effects of silver nanoparticles (AgNPs) on photosynthetic processes and biomass were investigated in aquatic plant Lemna gibba, and the plants were exposed to different concentrations of AgNPs for 7 days. At 7 day of exposure, a direct negative impact on the physiological state of plant was indicated by the decrease of chlorophyll (Chl) synthesis, the deterioration of photosynthetic activity and the change in biomass. When L. gibba was treated to 1 mg L-1 of AgNPs, total Chl content and the biomass decreased respectively by 66 and 51% compared to the control (P < 0.05). Under this condition, the alteration of photosystem II (PSII) photochemical reactions was indicated by a significant change compared to control of different studied fluorescence parameters value: F-V/F-M (35%), ET/RC (63%), VJ (61%), q(P) (57%) and NPQ (102%). Therefore, Chl a fluorescence measurements showed strong evidence of inhibitory effects on energy transfer from light harvesting complexes to reaction centers, the deterioration of the PSII water splitting system and the inactivation of PSII reaction centers at 1 mg L-1. In conclusion, our results demonstrated that AgNPs induced an inhibitory mechanism on photosynthetic processes and biomass of L. gibba plant.