title: A balanced PGR5 level is required for chloroplast development and optimum operation of cyclic electron transport around photosystem I.
abstract: PSI cyclic electron transport contributes markedly to photosynthesis and photoprotection in flowering plants. Although the thylakoid protein PGR5 (Proton Gradient Regulation 5) has been shown to be essential for the main route of PSI cyclic electron transport, its exact function remains unclear. In transgenic Arabidopsis plants overaccumulating PGR5 in the thylakoid membrane, chloroplast development was delayed, especially in the cotyledons. Although photosynthetic electron transport was not affected during steady-state photosynthesis, a high level of non-photochemical quenching (NPQ) was transiently induced after a shift of light conditions. This phenotype was explained by elevated activity of PSI cyclic electron transport, which was monitored in an in vitro system using ruptured chloroplasts, and also in leaves. The effect of overaccumulation of PGR5 was specific to the antimycin A-sensitive pathway of PSI cyclic electron transport but not to the NAD(P)H dehydrogenase (NDH) pathway. We propose that a balanced PGR5 level is required for efficient regulation of the rate of antimycin A-sensitive PSI cyclic electron transport, although the rate of PSI cyclic electron transport is probably also regulated by other factors during steady-state photosynthesis.
authors.affiliation: Graduate School of Agriculture, Kyushu University, 6-10-1 Hakozaki, Higashiku, Fukuoka, 812-8581 Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Okegawa
authors.forename: Terri A
authors.initials: TA
authors.lastname: Long
authors.forename: Megumi
authors.initials: M
authors.lastname: Iwano
authors.forename: Seiji
authors.initials: S
authors.lastname: Takayama
authors.forename: Yoshichika
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Sarah F
authors.initials: SF
authors.lastname: Covert
authors.forename: Toshiharu
authors.initials: T
authors.lastname: Shikanai
mesh_terms: D000968:Antimycin A / Q000494:pharmacology; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D018548:Cotyledon / Q000378:metabolism; D004579:Electron Transport / Q000502:physiology*; D018506:Gene Expression Regulation, Plant; D008027:Light; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism*; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D013997:Time Factors
chemical_list: D029681:Arabidopsis Proteins; C465062:PGR5 protein, Arabidopsis; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D000968:Antimycin A