title: The PSI-K subunit of photosystem I is involved in the interaction between light-harvesting complex I and the photosystem I reaction center core.
abstract: PSI-K is a subunit of photosystem I. The function of PSI-K was characterized in Arabidopsis plants transformed with a psaK cDNA in antisense orientation, and several lines without detectable PSI-K protein were identified. Plants without PSI-K have a 19% higher chlorophyll a/b ratio and 19% more P700 than wild-type plants. Thus, plants without PSI-K compensate by making more photosystem I. The photosystem I electron transport in vitro is unaffected in the absence of PSI-K. Light response curves for oxygen evolution indicated that the photosynthetic machinery of PSI-K-deficient plants have less capacity to utilize light energy. Plants without PSI-K have less state 1-state 2 transition. Thus, the redistribution of absorbed excitation energy between the two photosystems is reduced. Low temperature fluorescence emission spectra revealed a 2-nm blue shift in the long wavelength emission in plants lacking PSI-K. Furthermore, thylakoids and isolated PSI without PSI-K had 20-30% less Lhca2 and 30-40% less Lhca3, whereas Lhca1 and Lhca4 were unaffected. During electrophoresis under mildly denaturing conditions, all four Lhca subunits were partially dissociated from photosystem I lacking PSI-K. The observed effects demonstrate that PSI-K has a role in organizing the peripheral light-harvesting complexes on the core antenna of photosystem I.
authors.affiliation: Plant Biochemistry Laboratory, Department of Plant Biology, The Royal Veterinary and Agricultural University, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark. peje@kvl.dk
authors.forename: P E
authors.initials: PE
authors.lastname: Jensen
authors.forename: M
authors.initials: M
authors.lastname: Gilpin
authors.forename: J
authors.initials: J
authors.lastname: Knoetzel
authors.forename: H V
authors.initials: HV
authors.lastname: Scheller
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D016373:DNA, Antisense; D004579:Electron Transport; D007700:Kinetics; D008027:Light; D045342:Light-Harvesting Protein Complexes; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D045331:Photosystem I Protein Complex; D018515:Plant Leaves / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020524:Thylakoids / Q000378:metabolism
chemical_list: D016373:DNA, Antisense; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins; C074493:photosystem I, PSI-K subunit; D002734:Chlorophyll; C001785:chlorophyll P 700; C037184:chlorophyll b; D010100:Oxygen; D000077194:Chlorophyll A