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PresentationsEvaluation of methylmercury phytotoxicity by analyzing different chlorophyll fluorescence induction curvesDepartment of Biophysics, Faculty of Biology, M.V. Lomonosov Moscow State University, GSP-1, Leninskie Gory, Moscow, 119991, Russian Federation The chlorophyll fluorescence method is a popular method to study photosynthetic reactions at both normal and stress conditions, including the influence of anthropogenic pollutants. Among the fluorescence methods, the most popular is fluorescence kinetic curves (or OJIP curves) method due to the simplicity of registration, as well as the set of obtained parameters. Currently, there are fluorimeters, such as the multifunctional plant analyzer (M-PEA2), which simultaneously with OJIP curves records the induction curves of delayed chlorophyll fluorescence, as well as the redox activity of PSI at 820 nm. In this work, we applied this approach to study the effect of methylmercury (MeHg) on the primary photosynthetic reactions in green microalga Scenedesmus quadricauda. It was shown that MeHg at 0.1 μM slightly reduced the quantum yield of PSII (Fv/Fm ↓3%), while it caused an increase in the proportion of Qb-non-reducing centers (Vj ↑28%) and, consequently, decreased the quantum yield of electron transport at the level of Qa (φEo ↓20%) and the quinone pool (φRo ↓25%). A damage of donor side of PSII at the level of the quinone pool (peak K, Fv/Fo ↓72%), a decrease in the proportion of active RCs (ABS/RC ↑145%), and a significant increase in energy dissipation into heat (DIo/RC ↑441%) at 1 μM MeHg were detected. MeHg reduced the activity of PSI, which was manifested in a decrease in the oxidation rate of P700 and plastocyanin (PC). MeHg exposure resulted in changes in the delayed fluorescence induction curves associated with a decrease in energization of thylakoild membranes due to significant inhibition of electron transport at PSII and PSI. As an additional stress factor, we used photoinhibitory light to investigate the reparative abilities of PSII RCs in the presence of a wide range of MeHg concentrations from 0.01 to 10 μM. MeHg at 10 μM did not affect the quantum yield of PSII after 0.5 h of incubation, however, phytotoxicity at the selected concentration was enhanced in the presence of high light. After exposure to photoinhibitory light, PSII activity was recovered in the range from 0.01 to 2.5 μM MeHg, whereas at a concentration of 10 μM MeHg, the reparative abilities of PSII RCs were damaged.
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