Does ultraviolet radiation affect the xanthophyll cycle in marine phytoplankton?

This Perspective summarizes the state of knowledge of the impact of ultraviolet radiation on the photoprotective xanthophyll cycle in marine phytoplankton. Excess photosynthetically active radiation (PAR; 400-700 nm) and ultraviolet radiation (UVR; 280-400 nm) affect various cellular processes and can potentially lead to reduced growth or viability loss in situ. Algae deploy photoprotective mechanisms that limit the hazardous effects of excess light exposure. Xanthophyll cycle pigments play a crucial role in photoprotection via the development of non-photochemical fluorescence quenching (NPQ) during excess radiation exposure. Research on the interacting effects of excess PAR and UVR exposure on xanthophyll cycle pigment synthesis and xanthophyll cycle activity has produced contrasting views. The current contribution summarizes research on photoprotection via photoregulation (xanthophyll cycle activity) and photoacclimation (adjustment of the xanthophyll cycle pigment pool) for marine phytoplankton. Subsequently, UVR effects on the xanthophyll cycle and on xanthophyll cycle pigment pools are discussed and results of supporting experiments with the common diatom Thalassiosira weissflogii are presented. We show that UVR exposure may enhance xanthophyll cycle pigment synthesis. This suggests that UVR-induced reduction in de-epoxidation state does not necessarily imply reduced energy dissipating potential.