Investigating the photoprotective role of cytochrome b-559 in photosystem II in a mutant with altered ligation of the haem

Mary L. Hamilton, Emanuel Franco, Zsuzsanna Deák, Eberhard Schlodder, Imre Vass, Peter J. Nixon

Research output: Contribution to journalArticle

10 Citations (Scopus)


Despite many years of study, the physiological role of cytochrome b-559 (Cyt b-559) within the photosystem II (PSII) complex still remains unclear. Here we describe the analysis of a mutant of the green alga Chlamydomonas reinhardtii in which the His ligand to the haem, provided by the alpha subunit, has been replaced by a Cys residue. The mutant is unable to grow photoautotrophically but can assemble oxygen-evolving PSII supercomplexes to 15-20% of the levels found in the wild-type control. Haem is still detected in the isolated PSII supercomplexes but at sub-stoichiometric levels consistent with weaker binding to the mutated cytochrome. Analysis of PSII activity in cells indicates slowed electron transfer in the mutant between plastoquinones QA and QB. We show that PSII activity in the mutant is more sensitive to chronic photoinhibition than the WT control because of two effects: a faster rate of damage and an impaired PSII repair cycle at the level of synthesis and/or incorporation of D1 into PSII. We also demonstrate that Cyt b-559 plays a role during the critical stage of assembling the Mn 4CaO5 cluster. Overall we conclude that Cyt b-559 optimises electron transfer on the acceptor side of PSII and plays physiologically important roles in the assembly, repair and maintenance of the complex.

Original languageEnglish
Pages (from-to)1276-1285
Number of pages10
JournalPlant and Cell Physiology
Issue number7
Publication statusPublished - Jul 2014


  • Chloroplast mutant
  • PSII repair
  • Photoinhibition

ASJC Scopus subject areas

  • Physiology
  • Plant Science
  • Cell Biology

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