title: The multiple roles of light-harvesting chlorophyll a/b-protein complexes define structure and optimize function of Arabidopsis chloroplasts: a study using two chlorophyll b-less mutants.
abstract: The multiple roles of light-harvesting chlorophyll a/b-protein complexes in the structure and function of Arabidopsis chloroplasts were investigated using two chlorophyll b-less mutants grown under metal halide lamps with a significant far-red component. In ch1-3, all six light-harvesting proteins of photosystem (PS) II were greatly decreased; in ch1-3lhcb5, Lhcb5 was completely absent while the other five proteins were further decreased. The thylakoids of ch1-3 were less negatively-charged than the wild type, and those of ch1-3lhcb5 were even less so. Despite the expected weaker electrostatic repulsion, however, thylakoids in leaves of the mutants were not well stacked, an effect we attribute to lower van der Waals attraction, lower electrostatic attraction between opposite charges, and the absence or instability of PSII supercomplexes and peripheral light-harvesting trimers. The quantum yield of oxygen evolution in leaves decreased from 0.109 (wild type) to 0.087 (ch1-3) and 0.081 (ch1-3lhcb5) O(2) (photon absorbed)(-1); we attribute this decrease to an excessive spillover from PSII to PSI, a limited PSII antenna, and increased light-independent thermal dissipation in PSII in the mutants. Destabilization of the donor side of PSII, indicated by slower electron donation to the redox-active tyrosine Y(Z)(*) in ch1-3, probably enhanced PSII susceptibility to photoinactivation, increased the non-functional PSII complexes in vivo, and further inactivated PSII complexes in vitro. The evolution of chlorophyll b-containing chloroplasts seems to fine-tune oxygenic photosynthesis.
authors.affiliation: School of Biology, College of Medicine, Biology and Environment, The Australian National University, Canberra, ACT 0200, Australia.
authors.forename: Eun-Ha
authors.initials: EH
authors.lastname: Kim
authors.forename: Xiao-Ping
authors.initials: XP
authors.lastname: Li
authors.forename: Reza
authors.initials: R
authors.lastname: Razeghifard
authors.forename: Jan M
authors.initials: JM
authors.lastname: Anderson
authors.forename: Krishna K
authors.initials: KK
authors.lastname: Niyogi
authors.forename: Barry J
authors.initials: BJ
authors.lastname: Pogson
authors.forename: Wah Soon
authors.initials: WS
authors.lastname: Chow
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002734:Chlorophyll / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002736:Chloroplasts / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D004578:Electron Spin Resonance Spectroscopy; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism / Q000502:physiology*; D015636:Magnesium Chloride / Q000737:chemistry; D009154:Mutation; D010084:Oxidation-Reduction; D010788:Photosynthesis; D013050:Spectrometry, Fluorescence; D020524:Thylakoids / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D045342:Light-Harvesting Protein Complexes; D015636:Magnesium Chloride; D002734:Chlorophyll; C037184:chlorophyll b