A simple routine for quantitative analysis of light and dark kinetics of photochemical and non-photochemical quenching of chlorophyll fluorescence in intact leaves

<p>Paper describes principles and application of a novel routine that enables the quantitative analysis of the photochemical O-J phase of the variable fluorescence F _v associated with the reversible photo-reduction of the secondary electron acceptor Q_A of photosystem II (PSII) in algae and intact leaves. The kinetic parameters that determine the variable fluorescence F ^PP(t) associated with the release of photochemical quenching are estimated from 10 μs time-resolved light-on and light-off responses of F _v induced by two subsequent light pulses of 0.25 (default) and 1000 ms duration, respectively. Application of these pulses allows estimations of (i) the actual value of the rate constants k _L and k _AB of the light excitation (photoreduction of Q_A) and of the dark re-oxidation of photoreduced Q_A (Q_A ^-), respectively, (ii) the actual maximal normalized variable fluorescence [nF _v] associated with 100 % photoreduction of Q_A of open RCs, and (iii) the actual size β of RCs in which the re-oxidation of Q_A ^- is largely suppressed (Q_B-nonreducing RC with k _AB ~ 0). The rate constants of the dark reversion of Fv associated with the release of photo-electrochemical quenching F ^PE and photo-electric stimulation F ^CET in the successive J-I and I-P parts of the thermal phase are in the range of (100 ms)^-1 and (1 s)^-1, respectively. The kinetics of fluorescence changes during and after the I-P phase are given special attention in relation to the hypothesis on the involvement of a Δμ _H+-dependent effect during this phase and thereafter. Paper closes with author's personal view on the demands that should be fulfilled for chlorophyll fluorescence methods being a correct and unchallenged signature of photosynthesis in algae and plants.