Volume 90, Nº 7 (2025): VOL 90, NO7 (2025)

Специальный выпуск журнала «Биохимия» «Новые достижения в фотобиохимии и фотобиофизике» посвящён современным исследованиям в области взаимодействия света с живыми организмами и, в частности, обнаружению биофизических и биохимических механизмов формирования биологических ответов на освещение. В этом специальном выпуске опубликованы статьи учёных, занимающихся научными исследованиями в данном направлении и представивших свои научные достижения на I региональном собрании Российского фотобиологического общества и Всероссийской конференции с международным участием «Современные проблемы фотобиологии и биофотоники», прошедших с 14 по 19 октября 2024 г. в г. Нижний Новгород на базе Нижегородского государственного университета им. Н.И. Лобачевского.

This review addresses photosynthetic control as a protective mechanism that prevents photoinhibition of photosystem I under conditions of imbalance between CO₂ assimilation during the Calvin–Benson–Bassham cycle and light reactions in the thylakoid photosynthetic apparatus. We discuss the pathways of photosystem I photoinhibition and describe protective mechanisms that prevent photodamage of photosystem I. We propose a hypothesis regarding the influence of photosynthetic control on formation of reactive oxygen species in photosystem I. pH-sensitivity of plastoquinol oxidation at the quinol-oxidizing (Qo) site of the cytochrome b₆f complex is analyzed, and function of two proton-conducting channels that release protons into the thylakoid lumen from the cytochrome b₆f complex is described. We examine impact of photosynthetic control on the functioning of the cytochrome b₆f complex itself, and propose a hypothesis regarding the preferential activation of photosynthetic control in the thylakoid grana, which ensures operation of the cyclic electron transport around photosystem I as a main protective mechanism.

142290 Pushchino, Moscow Region, Russia; e-mail: vsyulya20@yandex.ru

Methods of site-directed mutagenesis are successfully used in structural and functional studies of photosynthetic reaction centers (RCs). It has been noted that many mutations near electron transfer cofactors reduce the temperature stability of Cereibacter sphaeroides RCs and affect the number of RCs in membranes. We previously reported [Selikhanov et al. (2023) Membranes, 25, 154] that the introduction of inter-subunit disulfide bridges on the periplasmic or cytoplasmic surface of the complex promotes an increase in the thermal stability of C. sphaeroides RCs. In this work, an attempt was made to increase the thermal stability of the mutant RC with the Ile M206 – Gln substitution
by introducing inter-subunit disulfide bonds. This RC is of considerable interest for studying the mechanisms of early electron transfer processes in RCs. The effect of mutations on the amount of RCs in chromatophores was analyzed and it was found that the I(M206)Q mutation leads to a twofold decrease in the RC content in chromatophores, the introduction of disulfide bonds on the cytoplasmic or periplasmic sides of the complex reduces the amount of RCs in membranes by a third, the triple substitution I(M206)Q/G(M19)C/T(L214)C – almost 4 times, and substitutions
I(M206)Q/V(M84)C/G(L278)C lead to disruption of RC assembly in the membrane. It was shown that the introduction of an inter-subunit S-S bond on the cytoplasmic surface of the complex did not have a significant effect on the thermal stability of the I(M206)Q RC. Our own and literature data on the factors influencing the assembly processes and ensuring the stability of the structure of integral membrane complexes are discussed.

The knockout of either At3g01500 gene, or At3g52720 gene encoding Arabidopsis thaliana βCA1 and αCA1 carbonic anhydrases, respectively led to a lower CA activity of chloroplast stroma preparations from knockout mutant plants αCA1-KO and βCA1-KO compared with the activity of such preparations from wild-type (WT) plants. To identify differences in the photosynthetic characteristics of mutant and WT plants, they were grown in low light (LL, 50-70 µmol quanta∙m⁻²∙s⁻¹, natural conditions) and high light (HL, 400 µmol quanta∙m⁻²∙s⁻¹, stressful conditions). The rate of CO₂ assimilation measured at 400 µmoles quanta∙m⁻²∙s⁻¹ in αCA1-KO and βCA1-KO plants grown in LL was lower than in WT plants; in the circumstances, the rate of photosynthetic electron transport in αCA1-KO plants was lower, while in βCA1-KO plants higher than in WT; the CO₂ content in chloroplasts was lower in βCA1-KO than in both WT and αKA1-KO, where it differed little;
the value of the proton motive force was higher in βCA1-KO, and in αKA1-KO it was lower than in WT due to changes in the ΔpH value. The obtained results suggested that βCA1 facilitates the intake of inorganic carbon into chloroplasts, while αCA1 facilitates the conversion of bicarbonate into CO₂ in chloroplasts stroma for its use in the reaction catalyzed by Rubisco. In αKA1-KO and βCA1-KO, the expression levels of genes encoding other chloroplast CAs were markedly different
from the expression levels of these genes in WT; the patterns of the changes depended on the light intensity during cultivation. The content of hydrogen peroxide in leaves of both αCA1-KO and βCA1-KO plants was higher in LL and lower in HL than in WT. The expression levels of stress marker genes changed similarly in both types of mutant plants. The possible involvement of the chloroplast stroma CAs in the transmission of stress signals in higher plants are discussed.

Some microalgae are capable of light-dependent hydrogen production after a period of anaerobic adaptation, thus performing biophotolysis of water. The hydrogen production rate at the initial moment reaches the maximum rate of photosynthesis. However, this process is short-lived: the oxygen released during photosynthesis quickly inactivates the key enzyme of biophotolysis, hydrogenase, and inhibits its expression. Approaches have been developed to achieve sustained hydrogen production by microalgae. The most studied are approaches based on transferring microalgae to nutrient-deficient conditions. However, it is known that hydrogen production under nutrient deficiency is always accompanied by a decrease in the activity of photosystem II (PSII). Several mechanisms of PSII activity suppression have been described in the literature, and there is no consensus on which mechanism is the determining one. The aim of this work was to test the hypothesis that the implementation of a particular mechanism of PSII suppression depends not only on the type of stress but also on the growth conditions. For this purpose, a photoautotrophic culture of the microalga Chlamydomonas reinhardtii was grown under nitrogen or sulfur deficiency under different light regimes, and the implementation of the following mechanisms of PSII activity suppression was analyzed: over-reduction of the plastoquinone pool (coupled with over-reduction of the entire photosynthetic electron transport chain), decoupling of PSII (based on the kinetics of ascorbate accumulation and the JIP test), the violaxanthin cycle, anaerobic stress associated with the creation of a reducing redox potential of the culture suspension. It was found that the key mechanism determining hydrogen production is over-reduction of the plastoquinone pool. Other mechanisms are also implemented under various conditions but do not show a clear correlation with hydrogen production. The results obtained indicate that stress caused by starvation of cultures is a convenient approach for studying hydrogen production by microalgae, but due to the low activity of PSII, it is impractical. New approaches are required to create industrial systems based on microalgae, allowing the full realization of the photosynthetic potential of microalgae.

One of the acclimatory mechanisms of photosynthetic organisms to changing light conditions is the redistribution of antenna complexes between photosystems, the process known as state transitions. This process allows the amount of light energy absorbed by each photosystem to be regulated. Numerous studies have demonstrated that state transitions are inhibited under high light intensity; however, the exact mechanism of this inhibition remains unclear. In the present study, the effect of H₂O₂ at various concentrations on the state transition process was investigated using functionally active thylakoids isolated from Arabidopsis leaves. Additionally, the specific stage of this process affected by H₂O₂ was evaluated. To assess state transitions, low-temperature chlorophyll a fluorescence spectra (F, from 650 to 780 nm) were measured, and the F745/F685 ratio was calculated as an indicator of state transition activity. It was shown that the addition of H₂O₂ led to the inhibition of state transitions in low light. The addition of H₂O₂ to thylakoids under low light conditions resulted in a decreased accumulation of phosphorylated Lhcb1 and Lhcb2 proteins, which are involved in state transitions. This indicates that the inhibition of state transitions is likely a consequence of inhibited activity of the STN7 kinase. It is important to note that H₂O₂ at the concentrations used did not affect the rate of electron transport, indicating that the inhibition of STN7 kinase activity is not associated with a suppression of the photosynthetic electron transport chain functioning. Moreover, the study demonstrates the selective effect of H₂O₂ on the activity of the STN7 kinase: no decrease in the level of the phosphorylated photosystem II D1 protein, the substrate of the STN8 kinase, was observed upon H₂O₂ treatment. Thus, this work provides the first evidence of the H₂O₂-dependent inhibitory mechanism of STN7 kinase activity and, consequently, of the state transition process.

Multiple antibiotic resistance is one of the major security risks in the field of global health. One of the approaches to solving this problem is antimicrobial photodynamic therapy, but currently used clinical photosensitizers are not sufficiently effective against various pathogens. Polycationic molecular constructs enhance the binding and penetration of photosensitizers into poorly permeable gram-negative bacteria. One of the methods for obtaining such conjugates is the introduction of various polyethyleneimines into the photosensitizer molecule. In this work, a branched tetraamine was synthesized and introduced into pyrrole ring A of the natural chlorin molecule. The study assessed the photoinduced toxicity of the new photosensitizer in vitro against Staphylococcus aureus,
Enterococcus faecalis, Pseudomonas aeruginosa, and E. coli bacteria. It was established that the obtained chlorin with a branched polyamine residue had an increased bactericidal effect when irradiated with light compared to its structural precursor.