Modeling of the redox state dynamics in photosystem II of Chlorella pyrenoidosa Chick cells and leaves of spinach and Arabidopsis thaliana from single flash-induced fluorescence quantum yield changes on the 100 ns–10 s time scale

Abstract

The time courses of the photosystem II (PSII) redox states were analyzed with a model scheme supposing a fraction of 11-25 % semiquinone (with reduced [Formula: see text]) RCs in the dark. Patterns of single flash-induced transient fluorescence yield (SFITFY) measured for leaves (spinach and Arabidopsis (A.) thaliana) and the thermophilic alga Chlorella (C.) pyrenoidosa Chick (Steffen et al. Biochemistry 44:3123-3132, 2005; Belyaeva et al. Photosynth Res 98:105-119, 2008, Plant Physiol Biochem 77:49-59, 2014) were fitted with the PSII model. The simulations show that at high-light conditions the flash generated triplet carotenoid (3)Car(t) population is the main NPQ regulator decaying in the time interval of 6-8 μs. So the SFITFY increase up to the maximum level [Formula: see text]/F 0 (at ~50 μs) depends mainly on the flash energy. Transient electron redistributions on the RC redox cofactors were displayed to explain the SFITFY measured by weak light pulses during the PSII relaxation by electron transfer (ET) steps and coupled proton transfer on both the donor and the acceptor side of the PSII. The contribution of non-radiative charge recombination was taken into account. Analytical expressions for the laser flash, the (3)Car(t) decay and the work of the water-oxidizing complex (WOC) were used to improve the modeled P680(+) reduction by YZ in the state S 1 of the WOC. All parameter values were compared between spinach, A. thaliana leaves and C. pyrenoidosa alga cells and at different laser flash energies. ET from [Formula: see text] slower in alga as compared to leaf samples was elucidated by the dynamics of [Formula: see text] fractions to fit SFITFY data. Low membrane energization after the 10 ns single turnover flash was modeled: the ∆Ψ(t) amplitude (20 mV) is found to be about 5-fold smaller than under the continuous light induction; the time-independent lumen pHL, stroma pHS are fitted close to dark estimates. Depending on the flash energy used at 1.4, 4, 100 % the pHS in stroma is fitted to 7.3, 7.4, and 7.7, respectively. The biggest ∆pH difference between stroma and lumen was found to be 1.2, thus pH- dependent NPQ was not considered.

Thylakoid membrane model of the Chl a fluorescence transient and P700 induction kinetics in plant leaves

“…The improved PS II reaction scheme of Belyaeva et al (2008;2011a;2014) was fitted to the Single Flash Induced Transient Fluorescence Yield (SFITFY) data measured after 10-ns light flashes of different energies, in whole cells of thermophilic alga Chlorella pyrenoidosa Chick, leaves of Arabidopsis thaliana and spinach. The quantitative analysis by means of fitting to data was successful with our detailed PSII model and allowed to calculate the redox-state dynamics by analyzing: (1) the FI curves detected on leaves in vivo (or with ionophores) on the time scale up to 2 s (Belyaeva et al 2011b) and (2) the SFITFY measured using weak light pulses on the time scale 100 ns-10 s (Belyaeva et al 2015). This elaborated PSII model (Belyaeva et al 2011b(Belyaeva et al , 2015 was also verified as a separate block and incorporated into the scheme of the Thylakoid membrane model published earlier by Riznichenko et al (1999) (see also Lebedeva et al 2002;Belyaeva 2004;Rubin and Riznichenko 2009).…”

“…Various dissipative processes should be taken into account in order to quantify the Chl a FL yield data. Therefore, different energy dissipation reactions were parametrized in the PSII model block (Belyaeva et al 2006(Belyaeva et al , 2008(Belyaeva et al , 2011a(Belyaeva et al , b, 2014(Belyaeva et al , 2015.…”

“…3, 5) includes a modified PSII model block (Belyaeva et al 2015) that was integrated ( Fig. 4) COO --buffer groups.…”

“…This scheme was described in detail by Belyaeva et al (2008Belyaeva et al ( , 2011aBelyaeva et al ( , b, 2014Belyaeva et al ( , 2015. Each rectangle element in Fig.…”

“…Therefore, 3 9 2 9 2 9 4 = 48 hypothetical states exist in the PSII model network. But some combinations of carrier redox states were excluded (Lebedeva et al 2000;Belyaeva 2004;Belyaeva et al 2015) due to information about the rates and sequences of the primary photosynthetic reactions (Baake and Schlöder 1992;Dau 1994;Stirbet et al 1998;Lazár 2003). …”