title: Role of cyclic electron transport around photosystem I in regulating proton motive force.
abstract: In addition to ∆pH formed across the thylakoid membrane, membrane potential contributes to proton motive force (pmf) in chloroplasts. However, the regulation of photosynthetic electron transport is mediated solely by ∆pH. To assess the contribution of two cyclic electron transport pathways around photosystem I (one depending on PGR5/PGRL1 and one on NDH) to pmf formation, electrochromic shift (ECS) was analyzed in the Arabidopsis pgr5 mutant, NDH-defective mutants (ndhs and crr4-2), and their double mutants (ndhs pgr5 and crr4-2 pgr5). In pgr5, the size of the pmf, as represented by ECSt, was reduced by 30% to 47% compared with that in the wild type (WT). A gH+ parameter, which is considered to represent the activity of ATP synthase, was enhanced at high light intensities. However, gH+ recovered to its low-light levels after 20 min in the dark, implying that the elevation in gH+ is due to the disturbed regulation of ATP synthase rather than to photodamage. After long dark adaptation more than 2 h, gH+ was higher in pgr5 than in the WT. During induction of photosynthesis, gH+ was more rapidly elevated in pgr5 than that in the WT. Both results suggest that ATP synthase is not fully inactivated in the dark in pgr5. In the NDH-deficient mutants, ECSt was slightly but significantly lower than in the WT, whereas gH+ was not affected. In the double mutants, ECSt was even lower than in pgr5. These results suggest that both PGR5/PGRL1- and NDH-dependent pathways contribute to pmf formation, although to different extents. This article is part of a Special Issue entitled: Chloroplast Biogenesis.
authors.affiliation: Department of Botany, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Caijuan
authors.initials: C
authors.lastname: Wang
authors.affiliation: Department of Botany, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan; CREST, Japan Science and Technology Agency, Chiyoda-ku, Tokyo 102-0076, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamamoto
authors.affiliation: Department of Botany, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan; CREST, Japan Science and Technology Agency, Chiyoda-ku, Tokyo 102-0076, Japan. Electronic address: shikanai@pmg.bot.kyoto-u.ac.jp.
authors.forename: Toshiharu
authors.initials: T
authors.lastname: Shikanai
mesh_terms: D029681:Arabidopsis Proteins / Q000502:physiology; D002736:Chloroplasts / Q000502:physiology*; D004579:Electron Transport; D008027:Light; D045322:Photosynthetic Reaction Center Complex Proteins / Q000502:physiology; D045331:Photosystem I Protein Complex / Q000502:physiology*; D018892:Proton-Motive Force; D006180:Proton-Translocating ATPases / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; C465062:PGR5 protein, Arabidopsis; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D006180:Proton-Translocating ATPases
keywords: ATP synthase; Arabidopsis thaliana; Cyclic electron transport; Electrochromic shift; Proton conductivity; Proton motive force