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

Abstract

Diatoms and brown algae are major contributors to marine primary production. They are biologically diverse, with thousands of different species, and are extremely successful, occupying almost 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 in response to pronounced fluctuations in their natural light environment. Regulation of light harvesting, and the use of excitation energy, is largely based on effective dissipation of excessive energy as heat. Thermal dissipation of excitation energy is assessed as non-photochemical quenching of chlorophyll a fluorescence (NPQ). NPQ depends strongly on the conversion of xanthophylls: diadinoxanthin (Dd) to diatoxanthin (Dt) in the Dd-Dt cycle of diatoms and violaxanthin (V) to zeaxanthin (Z), via the intermediate antheraxanthin (A), in the VAZ cycle present in brown algae. Xanthophyll cycle (XC)-dependent thermal energy dissipation underlying NPQ represents one of the most important photoprotection mechanisms of diatoms and brown algae. In the present chapter, we review the biochemistry of XC enzymes 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 in diatoms based on the latest experimental findings. In the last section, we highlight the importance of XC-dependent photoprotection for the ecological success of diatoms and brown algae in their natural environments.