title: PSI-LHCI of Chlamydomonas reinhardtii: Increasing the absorption cross section without losing efficiency.
abstract: Photosystem I (PSI) is an essential component of photosynthetic membranes. Despite the high sequence and structural homologies, its absorption properties differ substantially in algae, plants and cyanobacteria. In particular it is characterized by the presence of low-energy chlorophylls (red forms), the number and the energy of which vary in different organisms. The PSI-LHCI (PSI-light harvesting complex I) complex of the green alga Chlamydomonas reinhardtii (C.r.) is significantly larger than that of plants, containing five additional light-harvesting complexes (together binding≈65 chlorophylls), and contains red forms with higher energy than plants. To understand how these differences influence excitation energy transfer and trapping in the system, we studied two PSI-LHCI C.r. particles, differing in antenna size and red-form content, using time-resolved fluorescence and compared them to plant PSI-LHCI. The excited state kinetics in C.r. shows the same average lifetime (50 ps) as in plants suggesting that the effect of antenna enlargement is compensated by higher energy red forms. The system equilibrates very fast, indicating that all Lhcas are well-connected, despite their long distance to the core. The differences between C.r. PSI-LHCI with and without Lhca2 and Lhca9 show that these Lhcas bind red forms, although not the red-most. The red-most forms are in (or functionally close to) other Lhcas and slow down the trapping, but hardly affect the quantum efficiency, which remains as high as 97% even in a complex that contains 235 chlorophylls.
authors: Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Institute for Lasers, Life and Biophotonics Amsterdam, LaserLaB Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
authors: Clotilde
authors: C
authors: Le Quiniou
authors: Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Institute for Lasers, Life and Biophotonics Amsterdam, LaserLaB Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
authors: Lijin
authors: L
authors: Tian
authors: Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Institute for Lasers, Life and Biophotonics Amsterdam, LaserLaB Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
authors: Bartlomiej
authors: B
authors: Drop
authors: Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Institute for Lasers, Life and Biophotonics Amsterdam, LaserLaB Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
authors: Emilie
authors: E
authors: Wientjes
authors: Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Institute for Lasers, Life and Biophotonics Amsterdam, LaserLaB Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
authors: Ivo H M
authors: IHM
authors: van Stokkum
authors: Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Institute for Lasers, Life and Biophotonics Amsterdam, LaserLaB Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
authors: Bart
authors: B
authors: van Oort
authors: Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Institute for Lasers, Life and Biophotonics Amsterdam, LaserLaB Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands. Electronic address: r.croce@vu.nl.
authors: Roberta
authors: R
authors: Croce
mesh_terms: D016825:Chlamydomonas reinhardtii / Q000737:chemistry* / Q000254:growth & development / Q000378:metabolism; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000378:metabolism; D045331:Photosystem I Protein Complex / Q000737:chemistry* / Q000378:metabolism; D013050:Spectrometry, Fluorescence
chemical_list: D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex
keywords: Chlamydomonas reinhardtii; Light-harvesting complex I; Photosystem I; Red forms; Time-resolved fluorescence; Trapping efficiency