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- Title
NDH-Mediated Cyclic Electron Flow Around Photosystem I is Crucial for C<sub>4</sub> Photosynthesis.
- Authors
nNoriko Ishikawa; Atsushi Takabayashi; Ko Noguchi; Youshi Tazoe; Hiroshi Yamamoto; von Caemmerer, Susanne; Fumihiko Sato; Tsuyoshi Endo
- Abstract
C4 photosynthesis exhibits efficient assimilation in ambient air by concentrating around ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) through a metabolic pathway called the C4 cycle. 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 C4 photosynthesis, although the contribution of NDH-mediated CEF is small in C3 photosynthesis. Here, we generated NDH-suppressed transformants of a C4 plant, Flaveria bidentis, and showed that the NDH-suppressed plants grow poorly, especially under lowlight conditions. CO2 assimilation 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 C4 photosynthesis. 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 C4 photosynthesis. Our results demonstrate that the physiological contribution of NDH-mediated CEF is greater in C4 photosynthesis than in photosynthesis, suggesting that the mechanism of PET in photosynthesis has changed from that in photosynthesis accompanying the changes in the mechanism of CO2 assimilation.
- Subjects
PHOTOSYSTEMS; PHOTOSYNTHESIS; PLANT photorespiration; PHOTOADDITION; OXYGENASES
- Publication
Plant & Cell Physiology, 2016, Vol 57, Issue 10, p2020
- ISSN
0032-0781
- Publication type
Article
- DOI
10.1093/pcp/pcw127