Photoprotection Mechanisms in Plants and Algae Bruno Robert CEA, Institute of Biology and Technology of Saclay, UMR 8221 CNRS, 91191 Gif sur Yvette, France. To survive in changing light environments, photosynthetic organisms like plants and algae have developed sophisticated photoprotective mechanisms, which occur at different levels (leaves, chloroplasts and proteins). Using a variety of methods, we have characterised the molecular basis underlying the fast response of plants and algae to light changes, as well as how these organisms quench potentially harmful chlorophyll triplet states, which occur in the photosynthetic apparatus with low but significant yield. All these mechanisms involve carotenoid molecules, the role of which is photosynthesis need to be re-assessed.