Chlorophyll fluorescence phenomena in chloroplasts on subnanosecond time-scales probed by picosecond pulse pairs

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

Research output: Contribution to journalArticlepeer-review

Abstract

Fluorescence enhancement phenomena and quenching by exciton-exciton annihilation on subnanosecond and nanosecond time-scales were investigated in spinach chloroplasts utilizing picosecond laser pulse pairs (530 nm, 30 ps wide) of equal intensity, spaced apart in time by variable delays of Δt = 0-6 ns. This new method was devised to study the effect of pulse energies (1·1010-2·1015 photons per cm2) on the overall fluorescence yield in order to deduce the degree of correlation between the two pulses as a function of Δt. In the case of open reaction centers (F0 state) in Photosystem II (PS II), it is shown that the quenching effect of excitons generated by the first pulse on the fluorescence yield of the second pulse diminishes with increasing Δt with a characteristic decorrelation time of 140 ± 60 ps. This effect is attributed to either (1) the decay of mobile excitons in the light-harvesting antenna pigment bed as these excitons migrate towards the PS II reaction centers and the associated smaller core antenna pigment pools, or (2) the decay of a quenching state of the reaction center (and/or core antenna) which appears following a rapid (less than 140 ps) trapping of the excitons initially created in the antenna pigment bed. The absence of a significant decay component of exciton quenchers with a lifetime comparable to the 300-600 ps intermediate phase of fluorescence decay kinetics suggests that this phase, although contributing to more than half of the integrated fluorescence emission signal, is not caused by freely mobile exitons migrating in a lake of pigments, but originates instead from smaller pigment pools to which the excitons have migrated. It is proposed that bimolecular exciton-exciton annihilation in these smaller domains dominates annihilation in the larger antenna pigment bed. In the case of closed reaction centers (Fmax state), the decorrelation time between the two pulses is increased to 400 ± 100 ps, which is also attributed to either a mobile exciton component or to the decay of a quenching state of the reaction center. At low pulse intensities (below approx. 2 · 1012 photons per cm2) anomalous fluorescence enhancement effects are noted, which are clearly linked to the existence of initially open PS II reaction centers. These enhancement effects are different from the well-known fluorescence induction phenomena which occur on longer time-scales, and are tentatively attributed to variations in the quenching efficiencies of transitory photochemical states of PS II reaction centers.

Original languageEnglish (US)
Pages (from-to)81-92
Number of pages12
JournalBBA - Bioenergetics
Volume806
Issue number1
DOIs
StatePublished - Jan 23 1985

Keywords

  • (Spinach chloroplast)
  • Chlorophyll fluorescence
  • Exciton
  • Fluorescence induction
  • Photosystem II
  • Reaction center

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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