title: Two mechanisms for dissipation of excess light in monomeric and trimeric light-harvesting complexes.
abstract: Oxygenic photoautotrophs require mechanisms for rapidly matching the level of chlorophyll excited states from light harvesting with the rate of electron transport from water to carbon dioxide. These photoprotective reactions prevent formation of reactive excited states and photoinhibition. The fastest response to excess illumination is the so-called non-photochemical quenching which, in higher plants, requires the luminal pH sensor PsbS and other yet unidentified components of the photosystem II antenna. Both trimeric light-harvesting complex II (LHCII) and monomeric LHC proteins have been indicated as site(s) of the heat-dissipative reactions. Different mechanisms have been proposed: energy transfer to a lutein quencher in trimers, formation of a zeaxanthin radical cation in monomers. Here, we report on the construction of a mutant lacking all monomeric LHC proteins but retaining LHCII trimers. Its non-photochemical quenching induction rate was substantially slower with respect to the wild type. A carotenoid radical cation signal was detected in the wild type, although it was lost in the mutant. We conclude that non-photochemical quenching is catalysed by two independent mechanisms, with the fastest activated response catalysed within monomeric LHC proteins depending on both zeaxanthin and lutein and on the formation of a radical cation. Trimeric LHCII was responsible for the slowly activated quenching component whereas inclusion in supercomplexes was not required. This latter activity does not depend on lutein nor on charge transfer events, whereas zeaxanthin was essential.
authors.affiliation: Dipartimento di Biotecnologie, Università di Verona, Strada Le Grazie 15, 37134 Verona, Italy.
authors.forename: Luca
authors.identifier: 0000-0001-9497-5156
authors.initials: L
authors.lastname: Dall'Osto
authors.affiliation: Dipartimento di Biotecnologie, Università di Verona, Strada Le Grazie 15, 37134 Verona, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Cazzaniga
authors.affiliation: Dipartimento di Biotecnologie, Università di Verona, Strada Le Grazie 15, 37134 Verona, Italy.
authors.forename: Mauro
authors.initials: M
authors.lastname: Bressan
authors.affiliation: Department of Chemical Physics, Lund University, Getingevägen 60, Lund S-22241, Sweden.
authors.forename: David
authors.initials: D
authors.lastname: Paleček
authors.affiliation: Department of Chemical Physics, Lund University, Getingevägen 60, Lund S-22241, Sweden.
authors.forename: Karel
authors.initials: K
authors.lastname: Židek
authors.affiliation: Howard Hughes Medical Institute, Department of Plant and Microbial Biology, University of California, Berkeley 94720-3102, California, USA.|Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley 94720, California, USA.
authors.forename: Krishna K
authors.initials: KK
authors.lastname: Niyogi
authors.affiliation: Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley 94720, California, USA.|Graduate Group in Applied Science and Technology, University of California, Berkeley 94720, California, USA.|Department of Chemistry, Hildebrand B77, University of California, Berkeley 94720-1460, California, USA.
authors.forename: Graham R
authors.initials: GR
authors.lastname: Fleming
authors.affiliation: Department of Chemical Physics, Lund University, Getingevägen 60, Lund S-22241, Sweden.
authors.forename: Donatas
authors.initials: D
authors.lastname: Zigmantas
authors.affiliation: Dipartimento di Biotecnologie, Università di Verona, Strada Le Grazie 15, 37134 Verona, Italy.|Consiglio Nazionale delle Ricerche (CNR), Istituto per la Protezione delle Piante (IPP), Via Madonna del Piano 10, 50019 Sesto Fiorentino, Firenze, Italy.
authors.forename: Roberto
authors.identifier: 0000-0002-4140-8446
authors.initials: R
authors.lastname: Bassi
mesh_terms: D017360:Arabidopsis / Q000737:chemistry / Q000502:physiology*; D002412:Cations / Q000378:metabolism; D004735:Energy Transfer; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000378:metabolism*; D014975:Lutein / Q000502:physiology*; D009154:Mutation; D055503:Protein Multimerization; D065146:Zeaxanthins / Q000502:physiology*
chemical_list: D002412:Cations; D045342:Light-Harvesting Protein Complexes; D065146:Zeaxanthins; D014975:Lutein