title: Cyanobacterial Light-Harvesting Phycobilisomes Uncouple From Photosystem I During Dark-To-Light Transitions.
abstract: Photosynthetic organisms cope with changes in light quality by balancing the excitation energy flow between photosystems I (PSI) and II (PSII) through a process called state transitions. Energy redistribution has been suggested to be achieved by movement of the light-harvesting phycobilisome between PSI and PSII, or by nanometre scale rearrangements of the recently discovered PBS-PSII-PSI megacomplexes. The alternative 'spillover' model, on the other hand, states that energy redistribution is achieved by mutual association/dissociation of PSI and PSII. State transitions have always been studied by changing the redox state of the electron carriers using electron transfer inhibitors, or by applying illumination conditions with different colours. However, the molecular events during natural dark-to-light transitions in cyanobacteria have largely been overlooked and still remain elusive. Here we investigated changes in excitation energy transfer from phycobilisomes to the photosystems upon dark-light transitions, using picosecond fluorescence spectroscopy. It appears that megacomplexes are not involved in these changes, and neither does spillover play a role. Instead, the phycobilisomes partly energetically uncouple from PSI in the light but hardly couple to PSII.
authors.affiliation: Laboratory of Biophysics, Wageningen University, P.O. Box 8128, 6700 ET, Wageningen, The Netherlands.|BioSolarCells, P.O. Box 98, 6700 AB Wageningen, The Netherlands.
authors.forename: Volha
authors.initials: V
authors.lastname: Chukhutsina
authors.affiliation: Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland.
authors.forename: Luca
authors.initials: L
authors.lastname: Bersanini
authors.affiliation: Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland.
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
authors.affiliation: Laboratory of Biophysics, Wageningen University, P.O. Box 8128, 6700 ET, Wageningen, The Netherlands.|BioSolarCells, P.O. Box 98, 6700 AB Wageningen, The Netherlands.|MicroSpectroscopy Centre, Wageningen University, 6703 HA Wageningen, The Netherlands.
authors.forename: Herbert
authors.initials: H
authors.lastname: van Amerongen
mesh_terms: D004579:Electron Transport; D004735:Energy Transfer / Q000502:physiology; D008027:Light; D010788:Photosynthesis / Q000502:physiology*; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D045524:Phycobilisomes / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D046939:Synechocystis / Q000378:metabolism*
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D045524:Phycobilisomes