Quenching of chlorophyll triplet states by carotenoids in algal light-harvesting complexes related to fucoxanthin-chlorophyll protein
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We have used time-resolved absorption and fluorescence spectroscopy with nanosecond resolution to study triplet energy transfer from chlorophylls to carotenoids in a protective process that prevents the formation of reactive singlet oxygen. The light-harvesting complexes studied were isolated from Chromera velia, belonging to a group Alveolata, and Xanthonema debile and Nannochloropsis oceanica, both from Stramenopiles. All three light-harvesting complexes are related to fucoxanthin-chlorophyll protein, but contain only chlorophyll a and no chlorophyll c. In addition, they differ in the carotenoid content. This composition of the complexes allowed us to study the quenching of chlorophyll a triplet states by different carotenoids in a comparable environment. The triplet states of chlorophylls bound to the light-harvesting complexes were quenched by carotenoids with an efficiency close to 100%. Carotenoid triplet states were observed to rise with a ~5 ns lifetime and were spectrally and kinetically homogeneous. The triplet states were formed predominantly on the red-most chlorophylls and were quenched by carotenoids which were further identified or at least spectrally characterized.
KeywordsAlgae Energy transfer Light harvesting Photoprotection Photosynthesis Transient spectroscopy
This study was supported by Czech Science Foundation projects P501/12/G055 and 14-01377P and by institutional funding RVO:60077344. Discussions with Prof. Herbert van Amerongen from the Wageningen University are greatly appreciated. We are indebted to Dr. Sarah Henry from Glasgow University for careful proofreading of the manuscript.
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