Nonphotochemical quenching in the prasinophyte Ostreococcus tauri

Abstract

The primary stress on photosynthetic organisms is their life-giving sun. To counteract this stress, eukaryotic photosynthesizers have developed methods to recruit light-harvesting carotenoids for photoprotection. During the xanthophyll cycle, violaxanthin is rapidly de-epoxidated to help quench energy flow from the reaction center. While this reaction is efficient in land plants, it is unproductive in the model alga Chlamydomonas reinhardtii. As the earliest branching green algal group, the prasinophytes are of primary interest to the origin of eukaryotic light-adaptation. Our work characterizes the xanthophyll cycle in the model prasinophyte Ostreococcus tauri. Under high-light stress, O. tauri effectively converts up to 50% of its violaxanthin to antheraxanthin to zeaxanthin. Spectroscopic analysis reveals that this conversion correlates to a large increase in non-photochemical quenching, indicative of an effective photoprotective measure. This rapid change is a useful adaptation under changing environmental conditions and is likely a necessary practice for this inter-tidal Ostreococcus species.