title: NDH-Mediated Cyclic Electron Flow Around Photosystem I is Crucial for C4 Photosynthesis.
abstract: C4photosynthesis exhibits efficient CO2assimilation in ambient air by concentrating CO2around ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) through a metabolic pathway called the C4cycle. It has been suggested that cyclic electron flow (CEF) around PSI mediated by chloroplast NADH dehydrogenase-like complex (NDH), an alternative pathway of photosynthetic electron transport (PET), plays a crucial role in C4photosynthesis, although the contribution of NDH-mediated CEF is small in C3photosynthesis. Here, we generated NDH-suppressed transformants of a C4plant, Flaveria bidentis, and showed that the NDH-suppressed plants grow poorly, especially under low-light conditions. CO2assimilation rates were consistently decreased in the NDH-suppressed plants under low and medium light intensities. Measurements of non-photochemical quenching (NPQ) of Chl fluorescence, the oxidation state of the reaction center of PSI (P700) and the electrochromic shift (ECS) of pigment absorbance indicated that proton translocation across the thylakoid membrane is impaired in the NDH-suppressed plants. Since proton translocation across the thylakoid membrane induces ATP production, these results suggest that NDH-mediated CEF plays a role in the supply of ATP which is required for C4photosynthesis. Such a role is more crucial when the light that is available for photosynthesis is limited and the energy production by PET becomes rate-determining for C4photosynthesis. Our results demonstrate that the physiological contribution of NDH-mediated CEF is greater in C4photosynthesis than in C3photosynthesis, suggesting that the mechanism of PET in C4photosynthesis has changed from that in C3photosynthesis accompanying the changes in the mechanism of CO2assimilation.
authors: Graduate School of Biostudies, Kyoto University, Kitashirakawa-Oiwakecho, Sakyoku, Kyoto, 606-8502 Japan.
authors: Noriko
authors: N
authors: Ishikawa
authors: Graduate School of Biostudies, Kyoto University, Kitashirakawa-Oiwakecho, Sakyoku, Kyoto, 606-8502 Japan.|Present address: Institute of Low Temperature Science, Hokkaido University, Kita-19, Nishi-8, Kita-ku, Sapporo, 060-0819 Japan.
authors: Atsushi
authors: A
authors: Takabayashi
authors: School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo, 192-0392 Japan.
authors: Ko
authors: K
authors: Noguchi
authors: Graduate School of Biostudies, Kyoto University, Kitashirakawa-Oiwakecho, Sakyoku, Kyoto, 606-8502 Japan.|Present address: Graduate School of Agricultural Science, Tohoku University, 1-1, Amamiya-machi, Tsutsumidori, Aoba-ku, Sendai, 981-8555 Japan.
authors: Youshi
authors: Y
authors: Tazoe
authors: Department of Botany, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwakecho, Sakyoku, Kyoto, 606-8502 Japan.
authors: Hiroshi
authors: H
authors: Yamamoto
authors: Research School of Biology, The Australian National University, Canberra, ACT, 0200, Australia.
authors: Susanne
authors: S
authors: von Caemmerer
authors: Graduate School of Biostudies, Kyoto University, Kitashirakawa-Oiwakecho, Sakyoku, Kyoto, 606-8502 Japan.
authors: Fumihiko
authors: F
authors: Sato
authors: Graduate School of Biostudies, Kyoto University, Kitashirakawa-Oiwakecho, Sakyoku, Kyoto, 606-8502 Japan tuendo@kais.kyoto-u.ac.jp.
authors: Tsuyoshi
authors: T
authors: Endo
mesh_terms: D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D004579:Electron Transport / Q000528:radiation effects; D037142:Flaveria / Q000201:enzymology* / Q000254:growth & development / Q000528:radiation effects; D008027:Light; D009245:NADH Dehydrogenase / Q000378:metabolism*; D010788:Photosynthesis / Q000528:radiation effects; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism / Q000528:radiation effects; D010940:Plant Proteins / Q000378:metabolism*; D034622:RNA Interference; D013057:Spectrum Analysis; D013489:Suppression, Genetic / Q000528:radiation effects; D014170:Transformation, Genetic / Q000528:radiation effects
chemical_list: D045331:Photosystem I Protein Complex; D010940:Plant Proteins; D002245:Carbon Dioxide; D002244:Carbon; D009245:NADH Dehydrogenase
keywords: ATP production; C4 photosynthesis; Chloroplast NADH dehydrogenase-like complex; Cyclic electron flow around PSI; Low-light condition; Proton translocation across the thylakoid membrane