title: Central role of cyclic electron transport around photosystem I in the regulation of photosynthesis.
abstract: Cyclic electron transport around photosystem I generates ATP without the accumulation of NADPH in chloroplasts. In angiosperms, electron transport consists of a PGR5-PGRL1 protein-dependent pathway and a chloroplast NADH dehydrogenase-like complex-dependent pathway. Most likely, the PGR5-PGRL1 pathway corresponds to the cyclic phosphorylation discovered by Arnon and contributes mainly to ΔpH formation in photosynthesis. ATP synthesis utilizes this ΔpH formed by both linear and PSI cyclic electron transport. Furthermore, acidification of the thylakoid lumen downregulates light energy utilization in photosystem II and also electron transport through the cytochrome b6f complex. In the absence of PGR5, chloroplast NDH compensates for the reduced ΔpH formation to some extent. Additionally, proton conductivity is upregulated, probably through ATPase, in pgr5 mutants. The photosynthetic machinery likely forms a complex network to maintain high photosynthesis activity under fluctuating light conditions.
authors.affiliation: Department of Botany, Graduate School of Science, Kyoto University, Sakyo-ku, 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: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000968:Antimycin A / Q000494:pharmacology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D002736:Chloroplasts / Q000201:enzymology / Q000378:metabolism / Q000528:radiation effects; D045346:Cytochrome b6f Complex / Q000378:metabolism; D004579:Electron Transport / Q000187:drug effects / Q000528:radiation effects; D005288:Ferredoxins / Q000378:metabolism; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D008027:Light; D019684:Magnoliopsida / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D009245:NADH Dehydrogenase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010084:Oxidation-Reduction; D010788:Photosynthesis / Q000528:radiation effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism; D045331:Photosystem I Protein Complex / Q000187:drug effects / Q000378:metabolism*; D010971:Plastoquinone / Q000378:metabolism; D011522:Protons
chemical_list: D029681:Arabidopsis Proteins; D005288:Ferredoxins; D008565:Membrane Proteins; C465062:PGR5 protein, Arabidopsis; C527375:PGRL1 protein, Arabidopsis; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D011522:Protons; D000968:Antimycin A; D000255:Adenosine Triphosphate; D045346:Cytochrome b6f Complex; D009245:NADH Dehydrogenase; D000251:Adenosine Triphosphatases; D010971:Plastoquinone