title: Carotenoid cation formation and the regulation of photosynthetic light harvesting.
abstract: Photosynthetic light harvesting in excess light is regulated by a process known as feedback deexcitation. Femtosecond transient absorption measurements on thylakoid membranes show selective formation of a carotenoid radical cation upon excitation of chlorophyll under conditions of maximum, steady-state feedback deexcitation. Studies on transgenic Arabidopsis thaliana plants confirmed that this carotenoid radical cation formation is correlated with feedback deexcitation and requires the presence of zeaxanthin, the specific carotenoid synthesized during high light exposure. These results indicate that energy transfer from chlorophyll molecules to a chlorophyllzeaxanthin heterodimer, which then undergoes charge separation, is the mechanism for excess energy dissipation during feedback deexcitation.
authors.affiliation: Department of Chemistry, University of California, Berkeley, CA 94720, USA.
authors.forename: Nancy E
authors.initials: NE
authors.lastname: Holt
authors.forename: Donatas
authors.initials: D
authors.lastname: Zigmantas
authors.forename: Leonas
authors.initials: L
authors.lastname: Valkunas
authors.forename: Xiao-Ping
authors.initials: XP
authors.lastname: Li
authors.forename: Krishna K
authors.initials: KK
authors.lastname: Niyogi
authors.forename: Graham R
authors.initials: GR
authors.lastname: Fleming
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism; D002412:Cations / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism*; D025461:Feedback, Physiological; D005609:Free Radicals; D006863:Hydrogen-Ion Concentration; D008027:Light; D045342:Light-Harvesting Protein Complexes; D009154:Mutation; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism; D030821:Plants, Genetically Modified; D013050:Spectrometry, Fluorescence; D013057:Spectrum Analysis; D018724:Spinacia oleracea; D020524:Thylakoids / Q000378:metabolism*; D024341:Xanthophylls; D065146:Zeaxanthins; D019207:beta Carotene / Q000031:analogs & derivatives* / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D002412:Cations; D005609:Free Radicals; D045342:Light-Harvesting Protein Complexes; C489731:NPQ4 protein, Arabidopsis; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D024341:Xanthophylls; D065146:Zeaxanthins; D019207:beta Carotene; D002734:Chlorophyll