title: Variety in excitation energy transfer processes from phycobilisomes to photosystems I and II.
abstract: The light-harvesting antennas of oxygenic photosynthetic organisms capture light energy and transfer it to the reaction centers of their photosystems. The light-harvesting antennas of cyanobacteria and red algae, called phycobilisomes (PBSs), supply light energy to both photosystem I (PSI) and photosystem II (PSII). However, the excitation energy transfer processes from PBS to PSI and PSII are not understood in detail. In the present study, the energy transfer processes from PBS to PSs in various cyanobacteria and red algae were examined in vivo by selectively exciting their PSs or PBSs, and measuring the resulting picosecond to nanosecond time-resolved fluorescences. By observing the delayed fluorescence spectrum of PBS-selective excitation in Arthrospira platensis, we demonstrated that energy transfer from PBS to PSI via PSII (PBS→PSII→PSI transfer) occurs even for PSI trimers. The contribution of PBS→PSII→PSI transfer was species dependent, being largest in the wild-type of red alga Pyropia yezoensis (formerly Porphyra yezoensis) and smallest in Synechococcus sp. PCC 7002. Comparing the time-resolved fluorescence after PSs- and PBS-selective excitation, we revealed that light energy flows from CP43 to CP47 by energy transfer between the neighboring PSII monomers in PBS-PSII supercomplexes. We also suggest two pathways of energy transfer: direct energy transfer from PBS to PSI (PBS→PSI transfer) and indirect transfer through PSII (PBS→PSII→PSI transfer). We also infer that PBS→PSI transfer conveys light energy to a lower-energy red chlorophyll than PBS→PSII→PSI transfer.
authors.affiliation: Graduate School of Science, Kobe University, Kobe, 657-8501, Japan.
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Ueno
authors.affiliation: Graduate School of Engineering, Kobe University, Kobe, 657-8501, Japan.
authors.forename: Shimpei
authors.initials: S
authors.lastname: Aikawa
authors.affiliation: Fisheries Technology Institute, Hyogo Prefectural Technology Center for Agriculture, Forestry and Fisheries, Akashi, Hyogo, 674-0093, Japan.
authors.forename: Kyosuke
authors.initials: K
authors.lastname: Niwa
authors.affiliation: RIKEN Nishina Center for Accelerator-Based Science, Wako, Saitama, 351-0198, Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Abe
authors.affiliation: Graduate School of Science, Kobe University, Kobe, 657-8501, Japan.|Kobe University Research Center for Inland Seas, Awaji, 656-2401, Japan.
authors.forename: Akio
authors.initials: A
authors.lastname: Murakami
authors.affiliation: Graduate School of Engineering, Kobe University, Kobe, 657-8501, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Kondo
authors.affiliation: Graduate School of Science, Kobe University, Kobe, 657-8501, Japan. akimoto@hawk.kobe-u.ac.jp.|Molecular Photoscience Research Center, Kobe University, Kobe, 657-8501, Japan. akimoto@hawk.kobe-u.ac.jp.
authors.forename: Seiji
authors.initials: S
authors.lastname: Akimoto
mesh_terms: D000458:Cyanobacteria / Q000378:metabolism*; D004735:Energy Transfer; D007700:Kinetics; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D045524:Phycobilisomes / Q000378:metabolism*; D000461:Rhodophyta / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013997:Time Factors
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D045524:Phycobilisomes
keywords: Cyanobacteria; Delayed fluorescence; Energy transfer; Photosystem; Phycobilisome; Red algae