title: CO2 response of cyclic electron flow around PSI (CEF-PSI) in tobacco leaves--relative electron fluxes through PSI and PSII determine the magnitude of non-photochemical quenching (NPQ) of Chl fluorescence.
abstract: We hypothesized that cyclic electron flow around photosystem I (CEF-PSI) participates in the induction of non-photochemical quenching (NPQ) of chlorophyll (Chl) fluorescence when the rate of photosynthetic linear electron flow (LEF) is electron-acceptor limited. To test this hypothesis, the relationships among photosynthesis rate, electron fluxes through both PSI and PSII [Je(PSI) and Je(PSII)] and Chl fluorescence parameters were analyzed simultaneously in intact leaves of tobacco plants at several light intensities and partial pressures of ambient CO2 (Ca). At low light intensities, decreasing Ca lowered the photosynthesis rate, but Je(PSI) and Je(PSII) remained constant. Je(PSI) was larger than Je(PSII), indicating the existence of CEF-PSI. Increasing the light intensity enhanced photosynthesis and both Je(PSI) and Je (PSII). Je(PSI)/Je(PSII) also increased at high light and at high light and low Ca combined, showing a strong, positive relationship with NPQ of Chl fluorescence. These results indicated that CEF-PSI contributed to the dissipation of photon energy in excess of that consumed by photosynthesis by driving NPQ of Chl fluorescence. The main physiological function of CEF-PSI in photosynthesis of higher plants is discussed.
authors.affiliation: Research Institute of Innovative Technology for the Earth, 9-2 Kizugawadai, Kizu-cho, Soraku-gun, Kyoto, 619-0292 Japan. cmiyake@rite.or.jp
authors.forename: Chikahiro
authors.initials: C
authors.lastname: Miyake
authors.forename: Momoko
authors.initials: M
authors.lastname: Miyata
authors.forename: Yuki
authors.initials: Y
authors.lastname: Shinzaki
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Tomizawa
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism* / Q000528:radiation effects; D002736:Chloroplasts / Q000502:physiology; D004307:Dose-Response Relationship, Radiation; D004579:Electron Transport; D008027:Light; D008856:Microscopy, Fluorescence / Q000379:methods; D010313:Partial Pressure; D017785:Photons; D010788:Photosynthesis / Q000502:physiology*; D045331:Photosystem I Protein Complex / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000502:physiology; D018515:Plant Leaves / Q000378:metabolism* / Q000528:radiation effects; D014026:Nicotiana / Q000502:physiology*
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D002245:Carbon Dioxide