title: The negative feedback molecular mechanism which regulates excitation level in the plant photosynthetic complex LHCII: towards identification of the energy dissipative state.
abstract: Overexcitation of the photosynthetic apparatus is potentially dangerous because it can cause oxidative damage. Photoprotection realized via the feedback de-excitation in the pigment-protein light-harvesting complex LHCII, embedded in the chloroplast lipid environment, was studied with use of the steady-state and time-resolved fluorescence spectroscopy techniques. Illumination of LHCII results in the pronounced singlet excitation quenching, demonstrated by decreased quantum yield of the chlorophyll a fluorescence and shortening of the fluorescence lifetimes. Analysis of the 77K chlorophyll a fluorescence emission spectra reveals that the light-driven excitation quenching in LHCII is associated with the intensity increase of the spectral band in the region of 700nm, relative to the principal band at 680nm. The average chlorophyll a fluorescence lifetime at 700nm changes drastically upon temperature decrease: from 1.04ns at 300K to 3.63ns at 77K. The results of the experiments lead us to conclude that: (i) the 700nm band is associated with the inter-trimer interactions which result in the formation of the chlorophyll low-energy states acting as energy traps and non-radiative dissipation centers; (ii) the Arrhenius analysis, supported by the results of the FTIR measurements, suggests that the photo-reaction can be associated with breaking of hydrogen bonds. Possible involvement of photo-isomerization of neoxanthin, reported previously (Biochim. Biophys. Acta 1807 (2011) 1237-1243) in generation of the low-energy traps in LHCII is discussed.
authors.affiliation: Department of Biophysics, Institute of Physics, Maria Curie-Sklodowska University, Lublin, Poland.
authors.forename: Monika
authors.initials: M
authors.lastname: Zubik
authors.forename: Rafal
authors.initials: R
authors.lastname: Luchowski
authors.forename: Michal
authors.initials: M
authors.lastname: Puzio
authors.forename: Ewa
authors.initials: E
authors.lastname: Janik
authors.forename: Joanna
authors.initials: J
authors.lastname: Bednarska
authors.forename: Wojciech
authors.initials: W
authors.lastname: Grudzinski
authors.forename: Wieslaw I
authors.initials: WI
authors.lastname: Gruszecki
mesh_terms: D002734:Chlorophyll / Q000737:chemistry; D000077194:Chlorophyll A; D025461:Feedback, Physiological; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013696:Temperature
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D002734:Chlorophyll; D000077194:Chlorophyll A