XVI International Botanical Congess

The involvement of excited and highly reactive intermediates in oxygenic photosynthesis poses unique problems for algae and plants with respect to the generation of reactive oxygen species. To protect the photosynthetic apparatus from oxidative damage, specific carotenoid pigments (xanthophylls) in the chloroplast are involved in quenching of excited chlorophyll and reactive oxygen species. The roles of carotenoids in photoprotection are being addressed by characterizing mutants of Chlamydomonas reinhardtii and Arabidopsis thaliana that are defective in xanthophyll metabolism. The Chlamydomonas npq1 lor1 double mutant, which is deficient in zeaxanthin and lutein, undergoes photo-oxidative bleaching in high light. Extragenic suppressors of npq1 lor1 identify new mutations affecting the xanthophyll biosynthetic pathway. Multiple antioxidant functions of zeaxanthin have been uncovered by analysis of Arabidopsis mutants defective in the xanthophyll cycle and/or thermal dissipation of excess absorbed light energy.