title: PsbS protein modulates non-photochemical chlorophyll fluorescence quenching in membranes depleted of photosystems.
abstract: Plants with varying levels of PsbS protein were grown on lincomycin. Enhanced levels of non-photochemical fluorescence quenching (NPQ) in over-expressers of the protein have been observed. This was accompanied by increased amplitude of the irreversible NPQ component, qI, previously considered to reflect mainly photoinhibition of PSII reaction centres (RCII). However, since RCIIs were largely absent the observed qI is likely to originate from the LHCII antenna. In chloroplasts of over-expressers of PsbS grown on lincomycin an abnormally large NPQ (∼7) was characterised by a 0.34 ns average chlorophyll fluorescence lifetime. Yet the lifetime in the Fm state was similar to that of wild-type plants. 77K fluorescence emission spectra revealed a specific 700 nm peak typical of LHCII aggregates as well as quenching of the PSI fluorescence at 730 nm. The aggregated state manifested itself as a clear change in the distance between LHCII complexes detected by freeze-fracture electron microscopy. Grana thylakoids in the quenched state revealed 3 times more aggregated LHCII particles compared to the dark-adapted state. Overall, the results directly demonstrate the importance of LHCII aggregation in the NPQ mechanism and show that the PSII supercomplex structure plays no role in formation of the observed quenching.
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK.
authors.forename: Maxwell A
authors.initials: MA
authors.lastname: Ware
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK.
authors.forename: Vasco
authors.initials: V
authors.lastname: Giovagnetti
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK.
authors.forename: Erica
authors.initials: E
authors.lastname: Belgio
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK. Electronic address: a.ruban@qmul.ac.uk.
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Ruban
mesh_terms: D017360:Arabidopsis / Q000166:cytology / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism*; D055786:Gene Knockout Techniques; D045342:Light-Harvesting Protein Complexes / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D008034:Lincomycin / Q000494:pharmacology; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013696:Temperature
chemical_list: D029681:Arabidopsis Proteins; D045342:Light-Harvesting Protein Complexes; C489731:NPQ4 protein, Arabidopsis; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D008034:Lincomycin
keywords: Arabidopsis; LHCII aggregation; Lincomycin; NPQ; PsbS