The pgr1 mutation in the Rieske subunit of the cytochrome b6f complex does not affect PGR5-dependent cyclic electron transport around photosystem I

Yuki Okegawa, Michito Tsuyama, Yoshichika Kobayashi, Toshiharu Shikanai

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Abstract

Although photosystem I (PSI) cyclic electron transport is essential for plants, our knowledge of the route taken by electrons is very limited. To assess whether ferredoxin (Fd) donates electrons directly to plastoquinone (PQ) or via a Q-cycle in the cytochrome (cyt) b6f complex in PSI cyclic electron transport, we characterized the activity of PSI cyclic electron transport in an Arabidopsis mutant, pgr1 (proton gradient regulation). In pgr1, Q-cycle activity was hypersensitive to acidification of the thylakoid lumen because of an amino acid alteration in the Rieske subunit of the cyt b6f complex, resulting in a conditional defect in Q-cycle activity. In vitro assays using ruptured chloroplasts did not show any difference in the activity of PGR5-dependent PQ reduction by Fd, which functions in PSI cyclic electron transport in vivo. In contrast to the pgr5 defect, the pgr1 defect did not show any synergistic effect on the quantum yield of photosystem II in crr2-2, a mutant in which NDH (NAD(P)H dehydrogenase) activity was impaired. Furthermore, the simultaneous determination of the quantum yields of both photosystems indicated that the ratio of linear and PSI cyclic electron transport was not significantly affected in pgr1. All the results indicated that the pgr1 mutation did not affect PGRS-dependent PQ reduction by Fd. The phenotypic differences between pgr1 and pgr5 indicate that maintenance of the proper balance of linear and PSI cyclic electron transport is essential for preventing over-reduction of the stroma.

Original languageEnglish
Pages (from-to)28332-28336
Number of pages5
JournalJournal of Biological Chemistry
Volume280
Issue number31
DOIs
Publication statusPublished - Aug 5 2005

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Cytochrome b6f Complex
Photosystem I Protein Complex
Electron Transport
Plastoquinone
Ferredoxins
Mutation
Activity Cycles
Quantum yield
Defects
Electrons
Thylakoids
Photosystem II Protein Complex
Acidification
Chloroplasts
Arabidopsis
NAD
Protons
Assays
Oxidoreductases
Maintenance

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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The pgr1 mutation in the Rieske subunit of the cytochrome b6f complex does not affect PGR5-dependent cyclic electron transport around photosystem I. / Okegawa, Yuki; Tsuyama, Michito; Kobayashi, Yoshichika; Shikanai, Toshiharu.

In: Journal of Biological Chemistry, Vol. 280, No. 31, 05.08.2005, p. 28332-28336.

Research output: Contribution to journalArticle

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