Evidence for a fluorescence yield change driven by a light-induced conformational change within photosystem II during the fast chlorophyll a fluorescence rise

Gert Schansker, Szilvia Z. Tóth, László Kovács, Alfred R. Holzwarth, Gyozo Garab

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Abstract

Experiments were carried out to identify a process co-determining with Q A the fluorescence rise between F 0 and F M. With 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea (DCMU), the fluorescence rise is sigmoidal, in its absence it is not. Lowering the temperature to - 10 °C the sigmoidicity is lost. It is shown that the sigmoidicity is due to the kinetic overlap between the reduction kinetics of Q A and a second process; an overlap that disappears at low temperature because the temperature dependences of the two processes differ. This second process can still relax at - 60 °C where recombination between Q A - and the donor side of photosystem (PS) II is blocked. This suggests that it is not a redox reaction but a conformational change can explain the data. Without DCMU, a reduced photosynthetic electron transport chain (ETC) is a pre-condition for reaching the F M. About 40% of the variable fluorescence relaxes in 100 ms. Re-induction while the ETC is still reduced takes a few ms and this is a photochemical process. The fact that the process can relax and be re-induced in the absence of changes in the redox state of the plastoquinone (PQ) pool implies that it is unrelated to the Q B-occupancy state and PQ-pool quenching. In both +/-DCMU the process studied represents ~ 30% of the fluorescence rise. The presented observations are best described within a conformational protein relaxation concept. In untreated leaves we assume that conformational changes are only induced when Q A is reduced and relax rapidly on re-oxidation. This would explain the relationship between the fluorescence rise and the ETC-reduction.

Original languageEnglish
Pages (from-to)1032-1043
Number of pages12
JournalBiochimica et Biophysica Acta - Bioenergetics
Volume1807
Issue number9
DOIs
Publication statusPublished - Sep 1 2011

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Keywords

  • Chl a fluorescence
  • Conformational change
  • DCMU
  • Delayed fluorescence
  • OJIP-transient
  • Thermal phase

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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