[The application of PS II model for the analysis of fluorescence yield transients induced by actinic single turnover flash in the time range from 100 ns to 10 s].

Changes in flash-induced fluorescence yield in preparations of thermophilic Chlorella pyrenoidosa Chick cells (native and in the presence of DCMU) were investigated in the time range from 100 ns to 10 s using a new measuring system. The results were analyzed by mathematical modeling of processes in photosystem II. It was shown that the detailed description of recombination (including nonradiative) processes in photosystem II is important to simulate the fluorescence yield transients induced by an actinic single turnover flash. The model photosystem II parameters were modified to describe the light-induced effects in the presence of DCMU. By comparing the theoretical fluorescence curves with experimental ones, we obtained the values of relative fluorescence yield and the FM/F0 ratio, which is typical for experimental data. As a result of simulation, the values of the model parameters (rate constants of electron transfers at the donor and acceptor sites of photosystem II, pH in stroma, initial redox state of the plastoquinone pool, the rate of plastoquinol oxidation, and the rate constants of nonradiative recombination processes) were determined.