Characterization of factors affecting the activity of photosystem I cyclic electron transport in chloroplasts

Yuki Okegawa, Yugo Kagawa, Yoshichika Kobayashi, Toshiharu Shikanai

Research output: Contribution to journalArticlepeer-review

80 Citations (Scopus)

Abstract

PSI cyclic electron transport is essential for photosynthesis and photoprotection. In higher plants, the antimycin A-sensitive pathway is the main route of electrons in PSI cyclic electron transport. Although a small thylakoid protein, PGR5 (PROTON GRADIENT REGULATION 5), is essential for this pathway, its function is still unclear, and there are numerous debates on the rate of electron transport in vivo and its regulation. To assess how PGR5-dependent PSI cyclic electron transport is regulated in vivo, we characterized its activity in ruptured chloroplasts isolated from Arabidopsis thaliana. The activity of ferredoxin (Fd)-dependent plastoquinone (PQ) reduction in the dark is impaired in the pgr5 mutant. Alkalinization of the reaction medium enhanced the activity of Fd-dependent PQ reduction in the wild type. Even weak actinic light (AL) illumination also markedly activated PGR5-dependent PSI cyclic electron transport in ruptured chloroplasts. Even in the presence of linear electron transport [11 μmol O2 (mg Chl)-1 h-1], PGR5-dependent PSI electron transport was detected as a difference in Chl fluorescence levels in ruptured chloroplasts. In the wild type, PGR5-dependent PSI cyclic electron transport competed with NADP+ photoreduction. These results suggest that the rate of PGR5-dependent PSI cyclic electron transport is high enough to balance the production ratio of ATP and NADPH during steady-state photosynthesis, consistently with the pgr5 mutant phenotype. Our results also suggest that the activity of PGR5-dependent PSI cyclic electron transport is regulated by the redox state of the NADPH pool.

Original languageEnglish
Pages (from-to)825-834
Number of pages10
JournalPlant and Cell Physiology
Volume49
Issue number5
DOIs
Publication statusPublished - May 2008
Externally publishedYes

Keywords

  • Antimycin A
  • Arabidopsis
  • Ferredoxin
  • PGR5
  • PSI cyclic electron transport
  • Redox regulation

ASJC Scopus subject areas

  • Physiology
  • Plant Science
  • Cell Biology

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