Delayed fluorescence: an in vivo method for electron transport studies and on line applications in limnology

Abstract

Delayed fluorescence (DF) only occurs in living cells. DF is a measure of the photosynthetic activity and it is the result of an electron hole recombination fluorescence (680 ¿ 740 nm) from the reaction center P680+ during dark-adaptation. DF can be observed over several minutes until a charge equilibrium between inner and outer side of the thylakoid membrane is reached. All photosynethically active pigments (chlorophylls, xanthophylls and phycobilins) contribute to charge separation at P680. The decay kinetics of the DF is influenced by 1) the ratios of the pumping rates at PSI and PSII, 2) PQ pool size (Chlorophyta vs. Cyanoprokaryota), 3) availability of CO2 and 4) electron blockers (herbicides). Exciting a cell suspension (algal cultures, phytoplankton or chloroplasts) by monochromatic light (400 ¿ 730 nm) DF action spectra can be measured. The different algal classes contain different photosynethetically active pigments and therefore, show different DF excitation spectra. Growth conditions (e.g. high light) influence the efficiency of charge separation at the reaction centers and therefore, DF excitation spectra change (see S22-039: Bodemer). Applications in limnology: DF decay kinetics are used to determine the concentration of photosynthetically active pigments in vivo and netto growth rates in freshwaters. Herbicides can be detected by evaluating the difference in the decay kinetic of poisoned and unpoisoned algal cultures (bio-monitoring). DF excitation spectroscopy is used to analyze the phytoplankton composition in freshwaters.