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

Willem Vermaas, Govindjee

Research output: Contribution to journalArticle

28 Citations (Scopus)

Abstract

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
Volume680
Issue number2
DOIs
StatePublished - May 19 1982
Externally publishedYes

Fingerprint

Diuron
Bicarbonates
Fluorescence
Thylakoids
Photosystem II Protein Complex
Membranes
Electron Transport
Hot Temperature
Electrons
Oxidation
Kinetics
chlorophyll a
Experiments
benzoquinone
P-680

Keywords

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

ASJC Scopus subject areas

  • Biophysics

Cite this

Bicarbonate effects on chlorophyll a fluorescence transients in the presence and the absence of diuron. / Vermaas, Willem; Govindjee.

In: BBA - Bioenergetics, Vol. 680, No. 2, 19.05.1982, p. 202-209.

Research output: Contribution to journalArticle

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