Journal Article

CO<sub>2</sub> 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

Chikahiro Miyake, Momoko Miyata, Yuki Shinzaki and Ken-ichi Tomizawa

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 46, issue 4, pages 629-637
Published in print April 2005 | ISSN: 0032-0781
Published online April 2005 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pci067
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

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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.

Keywords: A/Ci; CO2; Cyclic electron flow; Non-photochemical quenching (NPQ); Photosynthesis; PSI; Ca, ambient CO2; CEF-PSI, cyclic electron flow around PSI; Ci, intercellular partial pressure of CO2; Je(PSI)/(PSII), electron fluxes through PSI/PSII; LEF, linear electron flow; LHC, light-harvesting complex; NPQ, non-photochemical quenching; PCO, photorespiratory carbon oxidation; PCR, photosynthetic carbon reduction; Φ(PSI)/(PSII), quantum yield of PSI/PSII; Rubisco, ribulose-1,5-bisphosphate carboxylase/oxygenase; RuBP, ribulose-1,5-bisphosphate

Journal Article.  6487 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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