title: Energy dissipation in photosynthesis: does the quenching of chlorophyll fluorescence originate from antenna complexes of photosystem II or from the reaction center?
abstract: Dissipation of light energy was studied in the moss Rhytidiadelphus squarrosus (Hedw.) Warnst., and in leaves of Spinacia oleracea L. and Arabidopsis thaliana (L.) Heynh., using chlorophyll fluorescence as an indicator reaction. Maximum chlorophyll fluorescence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)-treated spinach leaves, as produced by saturating light and studied between and -20 degrees C, revealed an activation energy delta E of 0.11 eV. As this suggested recombination fluorescence produced by charge recombination between the oxidized primary donor of photosystem II and reduced pheophytin, a mathematical model explaining fluorescence, and based in part on known characteristics of primary electron-transport reactions, was developed. The model permitted analysis of different modes of fluorescence quenching, two localized in the reaction center of photosystem II and one in the light-harvesting system of the antenna complexes. It predicted differences in the relationship between quenching of variable fluorescence Fv and quenching of basal, so-called F0 fluorescence depending on whether quenching originated from antenna complexes or from reaction centers. Such differences were found experimentally, suggesting antenna quenching as the predominant mechanism of dissipation of light energy in the moss Rhytidiadelphus, whereas reaction-center quenching appeared to be important in spinach and Arabidopsis. Both reaction-center and antenna quenching required activation by thylakoid protonation but only antenna quenching depended on or was strongly enhanced by zeaxanthin. De-protonation permitted relaxation of this quenching with half-times below 1 min. More slowly reversible quenching, tentatively identified as so-called qI or photoinhibitory quenching, required protonation but persisted for prolonged times after de-protonation. It appeared to originate in reaction centers.
authors.affiliation: Julius von Sachs-Institut für Biowissenschaften, Universität Würzburg, 97082 Würzburg, Germany.
authors.forename: N G
authors.initials: NG
authors.lastname: Bukhov
authors.forename: U
authors.initials: U
authors.lastname: Heber
authors.forename: C
authors.initials: C
authors.lastname: Wiese
authors.forename: V A
authors.initials: VA
authors.lastname: Shuvalov
mesh_terms: D019068:Bryopsida / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D002245:Carbon Dioxide / Q000494:pharmacology; D002734:Chlorophyll / Q000737:chemistry / Q000502:physiology* / Q000528:radiation effects; D003080:Cold Temperature; D004237:Diuron / Q000494:pharmacology; D004579:Electron Transport; D005453:Fluorescence; D006540:Herbicides / Q000494:pharmacology; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008954:Models, Biological; D010674:Pheophytins / Q000737:chemistry / Q000502:physiology / Q000528:radiation effects; D010777:Photochemistry; D010788:Photosynthesis / Q000502:physiology* / Q000528:radiation effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D018515:Plant Leaves / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D018724:Spinacia oleracea / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D013696:Temperature; D024341:Xanthophylls; D065146:Zeaxanthins; D019207:beta Carotene / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D006540:Herbicides; D045342:Light-Harvesting Protein Complexes; D010674:Pheophytins; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D024341:Xanthophylls; D065146:Zeaxanthins; D019207:beta Carotene; D002734:Chlorophyll; D002245:Carbon Dioxide; D004237:Diuron