Dynamics of in vivo membrane processes in algal thylakoids as analyzed from chlorophyll fluorescence induction using the photosystem II and thylakoid modelsстатья
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Аннотация:The OJIPSMT pattern of Chl a fluorescence induction (FI) was obtained with microalgae cells Scenedesmus obliquus (Scenedesmus) exposed after dark adaptation to moderate and high light intensities (1200 and 1800 μmol photon m–2 s–1) in the time range from the microseconds to 10 minutes. The fast and, particularly, slow OJIPS(M)T stages of FI extending up to 100 seconds were quantitatively described by fitting the thylakoid membrane (TM) model. The calculations adequately reproduced the dynamics of P700 oxidoreduction transients. The parameters of the TM processes (Table 1) were determined, and the transients of the TM model variables are shown in calculations. The dynamic stages of redox reactions in the reaction centers (RCs) of the photosystem II (PSII), the PQ/PQH2 quinone pool, the cytochrome b6f complex (Cyt bf), and P700 of PSI RCs are influenced by the adaptation of the TM system to light. In silico analysis revealed the role of the Cyt bf in the regulation of electron fluxes, when bL/H hemes remain in a more reduced state at high light intensity than at moderate illumination in the interval from 100 ms to 3 s. For non-radiative recombination of the separated charges in the RC Phe–P680+ and QA− P680+, the dependence of the rate constants k42-49 on the level of QB(2)– reduction was revealed, together with the dependence of k42-49 on the illumination of chloroplasts. Setting the dynamic rate constants kFNR(t) and kD-qE(t) allows comparing the generation ΔpHo-i(t)= pHS(t)–pHL(t), initiation of qE-quenching at pHL|Trigg =6.7, activation in the light FNR –reductase, and reaching the stationary charge flows up to 1-2 minutes of light induction. The fitting model of isolated PSII according to phytoplankton FI signals (Table 3) revealed the similarity of electron transfer parameters in PS2 RCs in monocultures such as Scenedesmus, Chlorella, and phytoplankton samples. The markers of the phytocenosis condition deviated only in the case of the degradation of a water reservoir compared to an ecologically clean one. These differences in markers consist in the reduced size of the antennas, an enhanced energy dissipation, and the pH decrease in the lumen.