Photosynthetic response in wheat plants caused by the phototoxicity of fluoranthene
Environmental organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) affect photosynthetic performance in plants. The photooxidation of PAHs in natural sunlight, especially UV radiation, enhances the toxicity of PAHs. However, it is unclear as how these compounds and their photoproducts affect the photosynthetic apparatus. In this study, measurements of PSI and PSII were simultaneously performed in wheat (Triticum aestivum L.) plants treated with fluoranthene (FLT) and photomodified fluoranthene (PFLT). The study aimed to investigate whether the phototoxicity of FLT has a different mechanism of toxicity on the two photosystems. With regard to PSII, FLT and PFLT produced a significant decrease in the quantum yield of PSII and a pronounced increase in the yield of nonregulated energy dissipation. A significant reduction was observed in the yield of nonphotochemical quenching. The toxic effects of the PFLT treatment on PSII’s performance were more pronounced. Likewise, we noted severe disruption in the electron transport rate in PSII and a decline in Fm caused by FLT phototoxicity. A decline in the quantum yield of PSI and an increase in donor and acceptor side limitation were observed concomitantly. The impact of PFLT was more evident than that of FLT. The data demonstrated that PSI is more tolerant of FLT but for PFLT, particularly at higher concentrations, a pronounced inhibition was observed in the oxidation–reduction kinetics of P700. All these data suggest that increased cyclic electron flow can confer greater protection from FLT toxicity but not from toxicity induced by higher concentrations of PFLT.