title: Slowly reversible de-epoxidation of lutein-epoxide in deep shade leaves of a tropical tree legume may 'lock-in' lutein-based photoprotection during acclimation to strong light.
abstract: The kinetics of response to strong light have been examined in deeply shaded leaves of the tropical tree legume (Inga sp.) which have extraordinarily high levels of the alpha-xanthophyll lutein-epoxide that are co-located in pigment-protein complexes of the photosynthetic apparatus with the beta-xanthophyll violaxanthin. As in other species, rapidly reversible photoprotection (measured as non-photochemical chlorophyll fluorescence quenching) is initiated within the time frame of sun-flecks (minutes), before detectable conversion of violaxanthin to antheraxanthin or zeaxanthin. Photoprotection is stabilized within hours of exposure to strong light by simultaneously engaging the reversible violaxanthin cycle and a slowly reversible conversion of lutein-epoxide to lutein. It is proposed that this lutein 'locks in' a primary mechanism of photoprotection during photoacclimation in this species, converting efficient light-harvesting antennae of the shade plant into potential excitation dissipating centres. It is hypothesized that lutein occupies sites L2 and V1 in light-harvesting chlorophyll protein complexes of photosystem II, facilitating enhanced photoprotection through the superior singlet and/or triplet chlorophyll quenching capacity of lutein.
authors.affiliation: Photobioenergetics Group, Research School of Biological Sciences, Australian National University, Box 475 Canberra, ACT 2601, Australia.
authors.forename: Shizue
authors.initials: S
authors.lastname: Matsubara
authors.forename: Maria
authors.initials: M
authors.lastname: Naumann
authors.forename: Robin
authors.initials: R
authors.lastname: Martin
authors.forename: Caroline
authors.initials: C
authors.lastname: Nichol
authors.forename: Uwe
authors.initials: U
authors.lastname: Rascher
authors.forename: Tomas
authors.initials: T
authors.lastname: Morosinotto
authors.forename: Roberto
authors.initials: R
authors.lastname: Bassi
authors.forename: Barry
authors.initials: B
authors.lastname: Osmond
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D002940:Circadian Rhythm; D004579:Electron Transport; D007887:Fabaceae / Q000378:metabolism / Q000502:physiology* / Q000528:radiation effects; D008027:Light; D014975:Lutein / Q000031:analogs & derivatives* / Q000378:metabolism*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000502:physiology; D010860:Pigments, Biological / Q000378:metabolism; D018515:Plant Leaves / Q000502:physiology; D014197:Trees / Q000502:physiology; D014329:Tropical Climate
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D010860:Pigments, Biological; D014975:Lutein