2015. This short article is published with open access at brb3.242 Springerlink.comAbstract Paper describes principles and dar.12119 application of a novel routine that enables the quantitative evaluation from the photochemical O phase in the variable fluorescence Fv associated together with the reversible photo-reduction with the secondary electron acceptor QA of photosystem II (PSII) in algae and intact leaves. The kinetic parameters that ascertain the variable fluorescence FPP(t) connected together with the release of photochemical quenching are estimated from 10 ls timeresolved light-on and light-off responses of Fv induced by two subsequent light pulses of 0.25 (default) and 1000 ms duration, respectively. Application of those pulses makes it possible for estimations of (i) the actual value on the price constants kL and kAB of your light excitation (photoreduction of QA) and with the dark re-oxidation of photoreduced QA (Q?), respectively, (ii) A the actual maximal normalized variable fluorescence [nFv] connected with one hundred photoreduction of QA of open RCs, and (iii) the actual size b of RCs in which the re-oxidation of Q?is largely suppressed (QB-nonreducing RC with a kAB * 0). The price constants from the dark reversion of Fv associated together with the release of photo-electrochemical quenching FPE and photo-electric stimulation FCET within the successive J and I parts with the thermal phase are within the array of (100 ms)-1 and (1 s)-1, respectively. The kineticsof fluorescence alterations for the duration of and soon after the I phase are offered special attention in relation towards the ., 2009; Gasser and Keller, 2009). As an illustration, from the age of three years youngsters hypothesis around the involvement of a DlH?-dependent effect through this phase and thereafter. Paper closes with author’s individual view around the demands that should be fulfilled for chlorophyll fluorescence procedures getting a right and unchallenged signature of photosynthesis in algae and plants. Keyword phrases Chlorophyll fluorescence kinetics ?Quenching mechanisms ?Technique analysis ?TSTM ?OJIP ?Views Abbreviations ?Fraction of Qb-nonreducing RCs DlH Transmembrane proton motive force DCMU 3(3,4-Dichlorophenyl)-1,1-dimethylurea dsq Donor side quenching FPE(t) Fluorescence emission at time t, relative to Fo, exclusively related with release of photoelectrochemical quenching FPP(t) Fluorescence emission at time t, relative to Fo, exclusively related with release of photochemical quenching FCET(t) Fluorescence emission at time t, relative to Fo, exclusively connected with photo-electric stimulation F0 Fluorescence amount of dark-adapted technique with 100 open RCs Fm Fluorescence level of dark-adapted method with one hundred closed RCs soon after fluorescence saturating pulse excitation STF P?Fluorescence level after excitation with STF or Fm SP, respectively of method in dark-adapted state PP Fluorescence level with 100 semi-closed RCs Fm following release of photochemical quenchingThis publication marks the 50th anniversary of author’s Ph.D. and– thesis on 26 May possibly 1965 in the University of Leiden (the Netherlands). W. Vredenberg Division of Plant Physiology, Wageningen University and Research, Wageningen, The Netherlands W. Vredenberg ( ) Department of Plant Physiology, Wageningen University and Research, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands e-mail: [email protected] FssPhotosynth Res (2015) 124:87?FIA kAB k2ABkL kqbfk-qbfkIP k-IP nFvOEC Ph(e) PSII QA QB qdsq RC SP sSP STF TSTM YZSteady state value in the light with the variable fluorescence connected exclusively with key photochemical quenching Fluorescence induction algorithm Rate continual of Q.