Reduced salinity interacts with ultraviolet radiation to alter photosystem II function in diatom Skeletonema costatum

Abstract

To investigate the effect of reduced salinity on diatoms’ capacity to cope with changing ultraviolet radiation (UVR) and photosynthetically active radiation (PAR), Skeletonema costatum was grown in a range of salinity (15, 25, and 35). The photosystem II (PSII) function was analyzed by increasing PAR and UVR to mimic a mixing event in turbulent waters. The results show that high UVR exposure significantly reduced PSII activity, especially in cells grown at low salinity. UVR, but not salinity, stimulated the ‘removal’ rate of PSII protein PsbA. Salinity alone, in the range of 15 to 35, did not regulate PSII acceptor region; however, the low salinity+UVR treatment decreased the energy flux for electron transport per PSII reaction center in S. costatum. It showed that low salinity exacerbated the damaging effect of UVR on PSII function in S. costatum by suppressing PsbA protein synthesis and modifying the photochemistry of PSII. Although higher catalase (CAT) activity and NPQs were induced, they were unable to prevent the combined damage effect of low salinity+UVR. Our findings indicate that reduced salinity and increased UVR potentially affect the abundance and distribution of S. costatum with the escalation of climate disturbances.