PARENT SESSION
Posters P4Ab Type II reaction centres: Acceptor side. Abstracts (272-288)

Origin of kinetic components of millisecond delayed chlorophyll fluorescence. Vassilij Goltsev^*,1, Ivelina Zaharieva¹, Petko Chernev¹, Petar Lambrev², Reto Strasser³, ¹ Department of Biophysics and Radiobiology, Sofia, Bulgaria² Institute of Biophysics, BAS, Sofia, Bulgaria, Sofia, Bulgaria³ Bioenergetics Laboratory, University of Geneva, JUSSY – GENÈVE, Switzerland

ABSTRACT- Delayed fluorescence (DF) dark decays in time interval from 0.35 to 5.5 ms are measured during dark to light adaptation in whole leaves using a disc phosphoroscope. The changes of DF features are compared with variable chlorophyll fluorescence simultaneously registered with the same apparatus as well as in parallel by Handy PEA (Hansatech Instrument Ltd.). The total DF signal is a sum of three components - sub-millisecond with life-time about 0.6 ms, millisecond decayed 2 - 4 ms and slow component with life-time >> 5.5 ms. The share of the three components in the integral DF varies during induction. In the first 20-30 ms of induction the sub-millisecond component has a main contribution, after 50-100 ms - the millisecond, and after 1 s the slow component has a significant part in DF signal. The lifetime of millisecond DF component increases from 0.5 s to 1 s of illumination and then returns to low level when the light steady state is reached. The amplitudes of millisecond and slow components as well as the lifetime of sub-millisecond component are sensitive to transmembrane electrical and proton gradient. The amplitude of the fastest component and the lifetime of millisecond component depend only on intersystem electron transfer rate. The temperature affects the three DF components in a different way not only in the induction period but also when the photosynthetic apparatus is in stationary light state. The data is discussed in terms of the role of different redox states of quinone photosystem II acceptors for formation of DF light quanta.

KEY WORDS: variable chlorophyll fluorescence, electron transfer, delayed fluorescence, Photosystem II