The Peculiar Features of Non-Photochemical Fluorescence Quenching in Diatoms and Brown Algae

International audienceDiatoms and brown algae are major contributors to marine primary production. They arebiologically diverse, with thousands of different species, and are extremely successful, occupyingalmost every marine ecosystem ranging from the coastal-estuarine to deep-sea regions.Their ecological success is based in part on their ability to rapidly regulate photosynthesis inresponse to pronounced fluctuations in their natural light environment. Regulation of light excessive energy as heat. Thermal dissipation of excitation energy is assessed as non-photochemicalquenching of chlorophyll a fluorescence (NPQ). NPQ depends strongly on theconversion of xanthophylls: diadinoxanthin (Dd) to diatoxanthin (Dt) in the Dd-Dt cycle ofdiatoms and violaxanthin (V) to zeaxanthin (Z), via the intermediate antheraxanthin (A), inthe VAZ cycle present in brown algae. Xanthophyll cycle (XC)-dependent thermal energydissipation underlying NPQ represents one of the most important photoprotection mechanismsof diatoms and brown algae. In the present chapter, we review the biochemistry of XCenzymes with a special focus on co-substrate requirements and regulation of enzyme activity.In addition, we present a new model for the structural basis of XC-dependent NPQ indiatoms based on the latest experimental findings. In the last section, we highlight the importanceof XC-dependent photoprotection for the ecological success of diatoms and brownalgae in their natural environments