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Oxygenic photosynthesis: induction of chlorophyll a fluorescence and regulation of electron transport in thylakoid membranes in silico

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1. Title Title of document Oxygenic photosynthesis: induction of chlorophyll a fluorescence and regulation of electron transport in thylakoid membranes in silico
2. Creator Author's name, affiliation, country A. V. Vershubskii; Moscow Lomonosov State University; Russian Federation
2. Creator Author's name, affiliation, country V. I. Priklonskii; Moscow Lomonosov State University; Russian Federation
2. Creator Author's name, affiliation, country A. N. Tikhonov; Moscow Lomonosov State University; Russian Federation
3. Subject Discipline(s)
3. Subject Keyword(s) chloroplasts; electron and proton transport; mathematical modeling
4. Description Abstract

The paper describes an extended mathematical model for the regulation of the key stages of electron transfer in the photosynthetic chain of electron transport (CET) and the associated processes of trans-thylakoid proton transfer and ATP synthesis in chloroplasts. This model includes primary plastoquinone PQA, associated with photosystem 2 (PS2), and secondary plastoquinone PQB, exchanging with plastoquinone molecules that are part of the pool of electronic carriers between PS2 and photosystem 1 (PS1). The model adequately describes the multiphase non-monotonic curves of chlorophyll fluorescence induction and the kinetics of P700 redox transformations (photoreaction center PS1), plastoquinone, changes in ATP and pH concentrations in lumen (pHin) and stroma (pHout) depending on the illuminating conditions of chloroplasts (variation in intensity and spectral composition of light). The results of computer simulation are consistent with experimental data on the kinetics of photoinduced P700 transformations in the leaves of higher plants and the induction of chlorophyll a fluorescence. The obtained data are discussed in the context of "short-term" mechanisms of pH-dependent regulation of electron transport in intact chloroplasts (non-photochemical quenching of excitation in PS2 and activation of Calvin–Benson cycle reactions).
5. Publisher Organizing agency, location The Russian Academy of Sciences
6. Contributor Sponsor(s) Volnoe Delo Foundation
7. Date (DD-MM-YYYY) 01.04.2025
8. Type Status & genre Peer-reviewed Article
8. Type Type Research Article
9. Format File format
10. Identifier Uniform Resource Identifier https://archivog.com/0233-4755/article/view/681132
10. Identifier Digital Object Identifier (DOI) 10.31857/S0233475525010015
10. Identifier eLIBRARY Document Number (EDN) uuknus
11. Source Title; vol., no. (year) Biologičeskie membrany; Vol 42, No 1 (2025)
12. Language English=en ru
13. Relation Supp. Files Fig. 1. The processes of electron and proton transport considered in the model and the scheme of compartmentalization of hydrogen ions and transmembrane proton fluxes described in the model. Designations: CBT – Calvin–Benson cycle; Fd – ferredoxin; FNR – ferredoxin-NADP reductase; CET – cyclic electron transport; P700 and P680 are the primary electron donors of photosystem 1 (PS1) and photosystem 2 (PS2), respectively; PQA – primary plastoquinone associated with photosystem 2 (PS2), PQB – secondary plastoquinone exchanged with plastoquinone molecules included in the pool of electron carriers between PS2 and photosystem 1 (PS1); Pc – plastocyanin; PQ – plastoquinone (oxidized form). РQH2 – plastoquinol (reduced form); b6 f – cytochrome complex b6 f; PTOX – terminal oxidases. (234KB)
Fig. 2. Scheme of the processes of energy migration and electron transfer on the acceptor side of PS2, considered within the framework of the present model for describing the induction of chlorophyll fluorescence. (82KB)
Fig. 3. Kinetics of chlorophyll fluorescence induction calculated for different intensities of incident light. Model parameters L1 and L2 (at L2/L1 = 1.5) correspond to the following light intensities: 1 = 100 quanta/s exciting PS1; 2 - 150 quanta/s; 3 - 300 quanta/s under the condition L2/L1 = 1.5. Other model parameters: L2/L1 = 1.5; [PQ]0/[P700]0 = 20. Initial conditions: [PQA(0)]/[PQA]0 = 0.01; [PQB(0)]/[PQB]0 = 0.1; [PQH2(0)]/[PQ]0 = 0.2. P700, [Pс(0)]/[Pс]0 = 0.005; and [Fd(0)]/[Fd]0 = 0.85. The constants of the reverse reactions kBQ and kAP680 (see Fig. 2) were assumed to be equal to zero. (90KB)
Fig. 4. Kinetic curves of photoinduced reduction of three forms of plastoquinone, PQA, PQB and n(PQH2)n, calculated for the intensity of the acting light corresponding to 150 quanta/s exciting PS2. The index “n” in the designation (PQH2)n indicates that n PQH2 molecules (relative to PS2) included in the pool of PQ/PQH2 molecules that are not directly bound to PS2 are considered. In the calculations, the results of which are presented in this figure, the total number of molecules of the plastoquinone pool (PQ + PQH2) was n = 10. Taking into account that the PQH2 molecule is a two-electron carrier, the maximum possible “electron capacity” of the plastoquinone pool is 20 equivalents. The values ​​of the remaining parameters of the model are the same as for the calculations, the results of which are presented in Fig. 3. (106KB)
Fig. 5. Kinetics of photoinduced changes in the concentrations of the oxidized form of the photoreaction center, calculated for different intensities of the acting light, indicated in the caption to Fig. 3: 1 – 100 quanta/s; 2 – 150 quanta/s; 3 – 300 quanta/s. The vertical arrows indicate the moments of turning the light on and off. (81KB)
Fig. 6. Kinetics of photoinduced changes in the concentrations of oxidized forms of plastocyanin (a) and ferredoxin (b) depending on the intensity of the incident light: 1 - 100 quanta/s; 2 - 150 quanta/s; 3 - 300 quanta/s. The vertical arrows indicate the moments of turning the light on and off. The relative concentration of Fd is equal to [Fd]0/[P700]0 = 8. (172KB)
Fig. 7. Kinetics of photoinduced changes in pH inside the thylakoids (pHin) and in the stroma (pHout) (panel a) and ATP concentration (panel b), calculated for different intensities of the acting light indicated in the caption to Fig. 3: 1 - 100 quanta/s; 2 - 150 quanta/s; 3 - 300 quanta/s. The vertical arrows indicate the moments of turning the light on and off. (160KB)
Fig. 8. Kinetics of chlorophyll fluorescence induction (a), photoinduced changes in the concentrations of the oxidized form of the photoreaction center P700+ (b), plastoquinol PQH2 (c), calculated at an incident light intensity of 150 quanta/s (at L2/L1 = 1.5) and different cyclic electron transport flows specified by the ratio of rate constants kFQ/kFN: 1 – kFQ/kFN = 0; 2 – kFQ/kFN = 0.15; 3 – kFQ/kFN = 0.35. (105KB)
Appendix (302KB)
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15. Rights Copyright and permissions Copyright (c) 2025 The Russian Academy of Sciences