Disturbance of photosystem II-oxygen evolution complex induced the oxidative damage in Chlorella vulgaris under the stress of cetyltrimethylammonium chloride.

Oxygen evolution complex (OEC) in photosystem II (PSII) is sensitive to environmental stressors. However, oxidative damage mechanism in PSII-OEC is still unclear. Here, we investigated photosynthetic performance of PSII, oxidative stress and antioxidant reaction induced by reactive oxygen species (ROS) in a unicellular green alga Chlorella vulgaris (C. vulgaris) under the stress of cetyltrimethylammonium chloride (CTAC). From the changes of chlorophyll fluorescence parameters and PSII activity, it was proved that the electron transport, which occurred initially at the electron donor side of OEC, was disturbed by CTAC. Moreover, a significant decrease of the oxygen evolution rate in OEC (40.95%) while an increase of ROS (50.50%) was obtained after the exposure to 0.6 mg/L CTAC compared to the control (without CTAC), confirming that more oxygen transferred to ROS under the stress. Furthermore, the increased ROS in chloroplast and the structural destruction in thylakoid membrane were observed, respectively. These results proved that oxidative damage mechanism in PSII-OEC is mainly through the reduction of oxygen evolution and the production of excessive ROS, thus leading to the destruction of OEC performance and chloroplast structure.