A model of photosystem II for the analysis of fast fluorescence rise in plant leaves

The polyphasic patterns of fluorescence induction rise in pea leaves in vivo and after the treatment with ionophores have been studied using a Plant Efficiency Analyzer. To analyze in detail photosystem II (PS II) electron transfer processes, an extended PS II model was applied, which included the sums of exponential functions to specify explicitly the light-driven formation of the transmembrane electric potential (ΔΨ(t)) as well as pH in the lumen (pHL(t)) and stroma (pHS(t)). PS II model parameters and numerical coefficients in ΔΨ(t), pHL(t), and pHS(t) were evaluated to fit fluorescence induction data for different experimental conditions: leaf in vivo or after ionophore treatment at low or high light intensity. The model imitated changes in the pattern of fluorescence induction rise due to the elimination of transmembrane potential in the presence of ionophores, when ΔΨ = 0 and pHL(t), pHS(t) changed to small extent relative to control values in vivo, with maximum ΔΨ(t) ~ 90 mV and ΔΨ(t) ~ 40 mV for the stationary state at ΔpH ≅ 1.8. As the light intensity was increased from 300 to 1200 μmol m-2 s-1, the heat dissipation rate constants increased threefold for nonradiative recombination of P680+Phe- and by ~30% for P680+QA-. The parameters ΔΨ, pHS and pHL were analyzed as factors of PS II redox state populations and fluorescence yield. The kinetic mechanism of fluorescence quenching is discussed, which is related with light-induced lumen acidification, when +QA- and P680+ recombination probability increases to regulate the QA reduction. © 2011 Pleiades Publishing, Ltd.