title: Enhancement of cyclic electron flow around PSI at high light and its contribution to the induction of non-photochemical quenching of chl fluorescence in intact leaves of tobacco plants.
abstract: Non-photochemical quenching (NPQ) of Chl fluorescence is a mechanism for dissipating excess photon energy and is dependent on the formation of a DeltapH across the thylakoid membranes. The role of cyclic electron flow around photosystem I (PSI) (CEF-PSI) in the formation of this DeltapH was elucidated by studying the relationships between O2-evolution rate [V(O2)], quantum yield of both PSII and PSI [Phi(PSII) and Phi(PSI)], and Chl fluorescence parameters measured simultaneously in intact leaves of tobacco plants in CO2-saturated air. Although increases in light intensity raised V(O2) and the relative electron fluxes through both PSII and PSI [Phi(PSII) x PFD and Phi(PSI) x PFD] only Phi(PSI) x PFD continued to increase after V(O2) and Phi(PSII) x PFD became light saturated. These results revealed the activity of an electron transport reaction in PSI not related to photosynthetic linear electron flow (LEF), namely CEF-PSI. NPQ of Chl fluorescence drastically increased after Phi(PSII) x PFD became light saturated and the values of NPQ correlated positively with the relative activity of CEF-PSI. At low temperatures, the light-saturation point of Phi(PSII) x PFD was lower than that of Phi(PSI) x PFD and NPQ was high. On the other hand, at high temperatures, the light-dependence curves of Phi(PSII) x PFD and Phi(PSI) x PFD corresponded completely and NPQ was not induced. These results indicate that limitation of LEF induced CEF-PSI, which, in turn, helped to dissipate excess photon energy by driving NPQ of Chl fluorescence.
authors.affiliation: Research Institute of Innovative Technology for the Earth (RITE), 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: Yuki
authors.initials: Y
authors.lastname: Shinzaki
authors.forename: Momoko
authors.initials: M
authors.lastname: Miyata
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Tomizawa
mesh_terms: D002734:Chlorophyll / Q000378:metabolism / Q000528:radiation effects*; D004579:Electron Transport / Q000502:physiology / Q000528:radiation effects; D005453:Fluorescence; D006863:Hydrogen-Ion Concentration / Q000528:radiation effects; D008027:Light; D010775:Photic Stimulation; D017785:Photons; D010788:Photosynthesis / Q000502:physiology / Q000528:radiation effects*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism / Q000528:radiation effects*; D045331:Photosystem I Protein Complex / Q000378:metabolism / Q000528:radiation effects; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects*; D013696:Temperature; D014026:Nicotiana / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects*
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D002734:Chlorophyll; C025167:P-680