The analysis of PS II photochemical activity using single and multi- turnover excitations

W.J. Vredenberg, M. Durchan, O. Prášil

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12 Citations (Scopus)

Abstract

Paper describes chlorophyll a fluorescence measurements in algal cells, and intact plant leaves and isolated chloroplasts. It focuses on amplitude and 10 µs-resolved kinetics of variable fluorescence responses upon excitation with fluorescence-saturating pulses (SP) and with 25 µs saturating single turnover flashes (STF) which are exposed before, during and after a 100 s actinic illumination (AL) of low and high intensity. In addition to the amply documented suppression of the maximal variable fluorescence from Fm to F’m, the relative proportion of the distinguished O-J- , J-I and I-P-phases of an SP-induced response is shown to be distinctly different in dark- and light-adapted leaves. The O-J-phase in the 0.01 to 1 ms time range is much less sensitive to light adaptation than the other phases in the 1 – 200 ms range. In algae and chloroplasts, the amplitude FmSTF of the STF-induced response is hardly affected by a shift from the dark- to the light-activated steady state. The results support the hypothesis that the maximal variable fluorescence Fm induced by a multiple-turnover, fluorescence-saturating pulse (SP), is associated with the release of photochemical and photoelectrochemical quenching. It is argued that the OJIPMT- or Kautsky induction curve of variable chlorophyll fluorescence in the 0 – 100 s time range is the reflection of the release of photochemical quenching supplemented with a temporary Photosystem I (PSI)-dependent photoelectric stimulation and transient release of photoelectrochemical quenching of radiative energy loss in the Photosystem II (PSII) antennas, rather than solely of a decrease in PSII photochemical activity as is usually concluded.
Original languageEnglish
Pages (from-to)45-54
JournalJournal of Photochemistry and Photobiology. B, Biology
Volume107
DOIs
Publication statusPublished - 2012

Keywords

  • chlorophyll-a fluorescence
  • photosystem-ii
  • in-vivo
  • photoelectrochemical control
  • induction kinetics
  • electron-transfer
  • higher-plants
  • redox state
  • flash
  • yield

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