Bicarbonate effects on chlorophyll a fluorescence transients in the presence and the absence of diuron

Wim F.J. Vermaas, Govindjee

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


We investigated the effect of HCO-3 addition to CO2-depleted thylakoids by means of fluorescence techniques. (1) In the presence of diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea), the net reduction of the primary quinone-type electron acceptor (Q) of Photosystem (PS) II is about 2-times faster in the absence of HCO-3 than in its presence, whether normal, heat-treated or NH2OH-treated samples are used. This effect of HCO-3 is, therefore, not on the O2-evolving apparatus. It is, however, interpreted to be due to an influence of HCO-3 on the kinetics of the reduction of Q, perhaps combined with an effect on the back reaction of Q- with P-680+, the oxidized form of the PS II reaction center chlorophyll a. (2) Fluorescence experiments in the absence of diuron indicate that the absence of HCO-3 results in a complete block at the quinone level; the area over the fluorescence induction curve in the absence of HCO-3 was found to be 2.2-times higher in the absence than in the presence of diuron, pointing to a complete block of BH2 oxidation in the absence of HCO-3. (3) No change in the midpoint potential of Q is observed when HCO-3 is added to CO2-depleted membranes. HCO-3 not only has a large (on/off) effect on the reoxidation of BH2, but also a smaller effect between P-680 and Q. We propose that HCO-3 binding to its specific site in the thylakoid membrane results in a conformational change, allowing normal electron transport between the two photosystems.

Original languageEnglish (US)
Pages (from-to)202-209
Number of pages8
JournalBBA - Bioenergetics
Issue number2
StatePublished - May 19 1982
Externally publishedYes


  • Bicarbonate effect
  • Chlorophyll
  • Dichlorophenyldimethylurea
  • Fluorescence
  • Photosystem II

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology


Dive into the research topics of 'Bicarbonate effects on chlorophyll a fluorescence transients in the presence and the absence of diuron'. Together they form a unique fingerprint.

Cite this