The time course of non-photochemical quenching in phycobilisomes of Synechocystis sp. PCC6803 as revealed by picosecond time-resolved fluorimetry |
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Authors: | E.G. Maksimov F.-J. Schmitt E.A. Shirshin M.D. Svirin I.V. Elanskaya T. Friedrich V.V. Fadeev V.Z. Paschenko A.B. Rubin |
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Affiliation: | 1. Department of Biophysics, Faculty of Biology, M.V. Lomonosov Moscow State University, 119992 Moscow, Russia;2. Institute of Chemistry, Biophysical Chemistry, TU Berlin, Straße des 17. Juni 135, D-10623 Berlin, Germany;3. Department of Quantum Electronics, Faculty of Physics, M.V. Lomonosov Moscow State University, 119992 Moscow, Russia;4. Department of Genetics, Faculty of Biology, M.V. Lomonosov Moscow State University, 119992 Moscow, Russia |
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Abstract: | As high-intensity solar radiation can lead to extensive damage of the photosynthetic apparatus, cyanobacteria have developed various protection mechanisms to reduce the effective excitation energy transfer (EET) from the antenna complexes to the reaction center. One of them is non-photochemical quenching (NPQ) of the phycobilisome (PB) fluorescence. In Synechocystis sp. PCC6803 this role is carried by the orange carotenoid protein (OCP), which reacts to high-intensity light by a series of conformational changes, enabling the binding of OCP to the PBs reducing the flow of energy into the photosystems. In this paper the mechanisms of energy migration in two mutant PB complexes of Synechocystis sp. were investigated and compared. The mutant CK is lacking phycocyanin in the PBs while the mutant ΔPSI/PSII does not contain both photosystems. Fluorescence decay spectra with picosecond time resolution were registered using a single photon counting technique. The studies were performed in a wide range of temperatures — from 4 to 300 K. The time course of NPQ and fluorescence recovery in darkness was studied at room temperature using both steady-state and time-resolved fluorescence measurements. The OCP induced NPQ has been shown to be due to EET from PB cores to the red form of OCP under photon flux densities up to 1000 μmol photons m− 2 s− 1. The gradual changes of the energy transfer rate from allophycocyanin to OCP were observed during the irradiation of the sample with blue light and consequent adaptation to darkness. This fact was interpreted as the revelation of intermolecular interaction between OCP and PB binding site. At low temperatures a significantly enhanced EET from allophycocyanin to terminal emitters has been shown, due to the decreased back transfer from terminal emitter to APC. The activation of OCP not only leads to fluorescence quenching, but also affects the rate constants of energy transfer as shown by model based analysis of the decay associated spectra. The results indicate that the ability of OCP to quench the fluorescence is strongly temperature dependent. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy. |
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Keywords: | PBs, phycobilisomes CK_PBs, phycobilisome cores from CK mutant PCB, phycocyanobilin PC, phycocyanin APC, allophycocyanin TE, terminal emitter PS II, photosystem II ROS, reactive oxygen species NPQ, non-photochemical quenching OCP, orange carotenoid protein FRP, fluorescence recovery protein τ, fluorescence lifetime φfl, fluorescence quantum yield TCSPC, time-correlated single photon counting DAS, decay associated spectra FWHM, full width at half maximum PDB, protein data bank |
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