Probing fluorescence induction in chloroplasts on a nanosecond time scale utilizing picosecond laser pulse pairs

J. Deprez, A. Dobek, N. E. Geacintov, G. Paillotin, J. Breton

Research output: Contribution to journalArticle

Abstract

The fluorescence induction and other fluorescence properties of spinach chloroplasts at room temperature were probed utilizing two 30-ps wide laser pulses (530 nm) spaced Δt (s) apart in time (Δt = 5-110 ns). The energy of the first pulse (P1) was varied (1012-1016 photons · cm-2), while the energy of the second (probe) pulse (P2) was held constant (5 · 1013 photons · cm-2). A gated (10 ns) optical multichannel analyzer-spectrograph system allowed for the detection of the fluorescence generated either by P1 alone, or by P2 alone (preceded by P1). The dominant effect observed for the fluorescence yield generated by P1 alone is the usual singlet-singlet exciton annihilation which gives rise to a decrease in the yield at high energies. However, when the fluorescence yield of dark-adapted chloroplasts is measured utilizing P2 (preceded by pulse P1) an increase in this yield is observed. The magnitude of this increase depends on Δt, and is characterized by a time constant of 28 ± 4 ns. This rise in the fluorescence yield is attributed to a reduction of the oxidized (by P1) reaction center P-680+ by a primary donor. At high pulse energies (P1 = 4 · 1014 photons · cm-2) the magnitude of this fluorescence induction is diminished by another quenching effect which is attributed to triplet excited states generated by intense P1 pulses. Assuming that the P1 pulse energy dependence of the fluorescence yield rise reflects the closing of the reaction centers, it is estimated that about 3-4 photon hits per reaction center are required to close completely the reaction centers, and that there are 185-210 chlorophyll molecules per Photosystem II reaction center.

Original languageEnglish (US)
Pages (from-to)444-454
Number of pages11
JournalBBA - Bioenergetics
Volume725
Issue number3
DOIs
StatePublished - Dec 30 1983

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Keywords

  • (Spinach chloroplast)
  • Exciton annihilation
  • Fluorescence induction
  • Photosystem II
  • Picosecond laser pulse
  • Reaction center

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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