Photosynthesis Research

, Volume 124, Issue 1, pp 31–44 | Cite as

Fluorescence relaxation in intact cells of photosynthetic bacteria: donor and acceptor side limitations of reopening of the reaction center

  • Emese Asztalos
  • Gábor Sipka
  • Péter MarótiEmail author
Regular Paper


The dark relaxation of the yield of variable BChl fluorescence in the 10−5–10 s time range is measured after laser diode (808 nm) excitation of variable duration in intact cells of photosynthetic bacteria Rba. sphaeroides, Rsp. rubrum, and Rvx. gelatinosus under various treatments of redox agents, inhibitors, and temperature. The kinetics of the relaxation is complex and much wider extended than a monoexponential function. The longer is the excitation, the slower is the relaxation which is determined by the redox states, sizes, and accessibility of the pools of cytochrome \(c_{2}^{2+}\) and quinone for donor and acceptor side-limited bacterial strains, respectively. The kinetics of fluorescence decay reflects the opening kinetics of the closed RC. The relaxation is controlled preferentially by the rate of re-reduction of the oxidized dimer by mobile cytochrome \(c_{2}^{2+}\) in Rba. sphaeroides and Rsp. rubrum and by the rate constant of the \({\rm{Q}}_{\rm{A}}^{-}\) interquinone electron transfer, (350 μs)−1 and/or the quinol/quinone exchange at the acceptor side in Rvx. gelatinosus. The commonly used acceptor side inhibitors (e.g., terbutryn) demonstrate kinetically limited block of re-oxidation of the primary quinone. The observations are interpreted in frame of a minimum kinetic and energetic model of electron transfer reactions in bacterial RC of intact cells.


Purple photosynthetic bacteria Reaction center Light-induced electron transfer Cytochromes Quinones 





Cytoplasmic membrane

cyt bc1

Cytochrome c 2 oxidoreductase

cyt \(c_{2}^{2+}\) and cyt \(c_{2}^{3+}\)

Reduced and oxidized cytochrome c 2, respectively


Intracytoplasmic membrane

LH1 and LH2

Core and peripheral light-harvesting complexes, respectively


Bacteriochlorophyll dimer

QA and QB

Primary and secondary acceptors (ubiquinones), respectively




Reaction center







Thanks to TÁMOP 4.2.2.A-11/1KONV-2012-0060, TÁMOP 4.2.2.B, and COST Actions on “Understanding Movement and Mechanism in Molecular Machines” (CM1306) programs for financial support.


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© Springer Science+Business Media Dordrecht 2014

Authors and Affiliations

  1. 1.Department of Medical PhysicsUniversity of SzegedSzegedHungary

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