Phycobilin/chlorophyll excitation equilibration upon carotenoid-induced non-photochemical fluorescence quenching in phycobilisomes of the cyanobacterium Synechocystis sp. PCC 6803 |
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Authors: | Marina G Rakhimberdieva Dmitrii V Vavilin Irina V Elanskaya |
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Institution: | a A.N. Bakh Institute of Biochemistry, Russian Academy of Sciences, 119071 Moscow, Russia b School of Life Sciences and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, AZ 85287, USA c Department of Genetics, Faculty of Biology, M.V. Lomonosov Moscow State University, 119992 Moscow, Russia |
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Abstract: | To determine the mechanism of carotenoid-sensitized non-photochemical quenching in cyanobacteria, the kinetics of blue-light-induced quenching and fluorescence spectra were studied in the wild type and mutants of Synechocystis sp. PCC 6803 grown with or without iron. The blue-light-induced quenching was observed in the wild type as well as in mutants lacking PS II or IsiA confirming that neither IsiA nor PS II is required for carotenoid-triggered fluorescence quenching. Both fluorescence at 660 nm (originating from phycobilisomes) and at 681 nm (which, upon 440 nm excitation originates mostly from chlorophyll) was quenched. However, no blue-light-induced changes in the fluorescence yield were observed in the apcE− mutant that lacks phycobilisome attachment. The results are interpreted to indicate that interaction of the Slr1963-associated carotenoid with - presumably - allophycocyanin in the phycobilisome core is responsible for non-photochemical energy quenching, and that excitations on chlorophyll in the thylakoid equilibrate sufficiently with excitations on allophycocyanin in wild type to contribute to quenching of chlorophyll fluorescence. |
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Keywords: | APC allophycocyanin Chl chlorophyll DCMU 3-(3 4-dichlorophenyl)-1 1-dimethylurea F+BL F&minus BL fluorescence yields of cells treated (+BL) or not treated (&minus BL) with blue actinic light LHCII light harvesting complex II NPQ non-photochemical quenching PS II (PS I) photosystem II (photosystem I) PBS phycobilisome PC phycocyanin TE terminal emitter |
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