title: The nature of self-regulation in photosynthetic light-harvesting antenna.
abstract: The photosynthetic apparatus of green plants is well known for its extremely high efficiency that allows them to operate under dim light conditions. On the other hand, intense sunlight may result in overexcitation of the light-harvesting antenna and the formation of reactive compounds capable of 'burning out' the whole photosynthetic unit. Non-photochemical quenching is a self-regulatory mechanism utilized by green plants on a molecular level that allows them to safely dissipate the detrimental excess excitation energy as heat. Although it is believed to take place in the plant's major light-harvesting complexes (LHC) II, there is still no consensus regarding its molecular nature. To get more insight into its physical origin, we performed high-resolution time-resolved fluorescence measurements of LHCII trimers and their aggregates across a wide temperature range. Based on simulations of the excitation energy transfer in the LHCII aggregate, we associate the red-emitting state, having fluorescence maximum at ∼700 nm, with the partial mixing of excitonic and chlorophyll-chlorophyll charge transfer states. On the other hand, the quenched state has a totally different nature and is related to the incoherent excitation transfer to the short-lived carotenoid excited states. Our results also show that the required level of photoprotection in vivo can be achieved by a very subtle change in the number of LHCIIs switched to the quenched state.
authors.affiliation: Department of Theoretical Physics, Faculty of Physics, Vilnius University, Saulėtekio Avenue 9, LT-10222 Vilnius, Lithuania.|Department of Molecular Compound Physics, Centre for Physical Sciences and Technology, Saulėtekio Avenue 3, LT-10222 Vilnius, Lithuania.
authors.forename: Jevgenij
authors.identifier: 0000-0002-7591-1373
authors.initials: J
authors.lastname: Chmeliov
authors.affiliation: Department of Theoretical Physics, Faculty of Physics, Vilnius University, Saulėtekio Avenue 9, LT-10222 Vilnius, Lithuania.|Department of Molecular Compound Physics, Centre for Physical Sciences and Technology, Saulėtekio Avenue 3, LT-10222 Vilnius, Lithuania.
authors.forename: Andrius
authors.initials: A
authors.lastname: Gelzinis
authors.affiliation: Department of Molecular Compound Physics, Centre for Physical Sciences and Technology, Saulėtekio Avenue 3, LT-10222 Vilnius, Lithuania.
authors.forename: Egidijus
authors.initials: E
authors.lastname: Songaila
authors.affiliation: Department of Molecular Compound Physics, Centre for Physical Sciences and Technology, Saulėtekio Avenue 3, LT-10222 Vilnius, Lithuania.
authors.forename: Ramūnas
authors.initials: R
authors.lastname: Augulis
authors.affiliation: The School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK.
authors.forename: Christopher D P
authors.initials: CD
authors.lastname: Duffy
authors.affiliation: The School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK.
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Ruban
authors.affiliation: Department of Theoretical Physics, Faculty of Physics, Vilnius University, Saulėtekio Avenue 9, LT-10222 Vilnius, Lithuania.|Department of Molecular Compound Physics, Centre for Physical Sciences and Technology, Saulėtekio Avenue 3, LT-10222 Vilnius, Lithuania.
authors.forename: Leonas
authors.initials: L
authors.lastname: Valkunas
mesh_terms: D005453:Fluorescence; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism*; D010788:Photosynthesis; D018515:Plant Leaves / Q000502:physiology*; D018724:Spinacia oleracea / Q000502:physiology*
chemical_list: D045342:Light-Harvesting Protein Complexes