Quenching of chlorophyll triplet states by carotenoids in algal light-harvesting complexes related to fucoxanthin-chlorophyll protein
Abstrakt
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.