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International Journal of Molecular... Mar 2024Photosystem I (PSI) is one of the two main pigment-protein complexes where the primary steps of oxygenic photosynthesis take place. This review describes low-temperature... (Review)
Review
Photosystem I (PSI) is one of the two main pigment-protein complexes where the primary steps of oxygenic photosynthesis take place. This review describes low-temperature frequency-domain experiments (absorption, emission, circular dichroism, resonant and non-resonant hole-burned spectra) and modeling efforts reported for PSI in recent years. In particular, we focus on the spectral hole-burning studies, which are not as common in photosynthesis research as the time-domain spectroscopies. Experimental and modeling data obtained for trimeric cyanobacterial Photosystem I (PSI), PSI mutants, and PSI-IsiA supercomplexes are analyzed to provide a more comprehensive understanding of their excitonic structure and excitation energy transfer (EET) processes. Detailed information on the excitonic structure of photosynthetic complexes is essential to determine the structure-function relationship. We will focus on the so-called "red antenna states" of cyanobacterial PSI, as these states play an important role in photochemical processes and EET pathways. The high-resolution data and modeling studies presented here provide additional information on the energetics of the lowest energy states and their chlorophyll (Chl) compositions, as well as the EET pathways and how they are altered by mutations. We present evidence that the low-energy traps observed in PSI are excitonically coupled states with significant charge-transfer (CT) character. The analysis presented for various optical spectra of PSI and PSI-IsiA supercomplexes allowed us to make inferences about EET from the IsiA ring to the PSI core and demonstrate that the number of entry points varies between sample preparations studied by different groups. In our most recent samples, there most likely are three entry points for EET from the IsiA ring per the PSI core monomer, with two of these entry points likely being located next to each other. Therefore, there are nine entry points from the IsiA ring to the PSI trimer. We anticipate that the data discussed below will stimulate further research in this area, providing even more insight into the structure-based models of these important cyanobacterial photosystems.
Topics: Photosystem I Protein Complex; Circular Dichroism; Energy Transfer; Chlorophyll; Cold Temperature
PubMed: 38612659
DOI: 10.3390/ijms25073850 -
Frontiers in Plant Science 2022Light intensity is highly heterogeneous in nature, and plants have evolved a series of strategies to acclimate to dynamic light due to their immobile lifestyles....
Light intensity is highly heterogeneous in nature, and plants have evolved a series of strategies to acclimate to dynamic light due to their immobile lifestyles. However, it is still unknown whether there are differences in photoprotective mechanisms among different light-demanding plants in response to dynamic light, and thus the role of non-photochemical quenching (NPQ), electron transport, and light energy allocation of photosystems in photoprotection needs to be further understood in different light-demanding plants. The activities of photosystem II (PSII) and photosystem I (PSI) in shade-tolerant species , intermediate species , and sun-demanding species were comparatively measured to elucidate photoprotection mechanisms in different light-demanding plants under dynamic light. The results showed that the NPQ and PSII maximum efficiency ( '/ ') of were higher than the other two species under dynamic high light. Meanwhile, cyclic electron flow (CEF) of sun plants is larger under transient high light conditions since the slope of post-illumination, P700 dark reduction rate, and plastoquinone (PQ) pool were greater. NPQ was more active and CEF was initiated more readily in shade plants than the two other species under transient light. Moreover, sun plants processed higher quantum yield of PSII photochemistry (Φ), quantum yield of photochemical energy conversion [Y(I)], and quantum yield of non-photochemical energy dissipation due to acceptor side limitation (Y(NA), while the constitutive thermal dissipation and fluorescence (Φ) and quantum yield of non-photochemical energy dissipation due to donor side limitation [Y(ND)] of PSI were higher in shade plants. These results suggest that sun plants had higher NPQ and CEF for photoprotection under transient high light and mainly allocated light energy through Φ and Φ, while shade plants had a higher Φ and a larger heat dissipation efficiency of PSI donor. Overall, it has been demonstrated that the photochemical efficiency and photoprotective capacity are greater in sun plants under transient dynamic light, while shade plants are more sensitive to transient dynamic light.
PubMed: 35463455
DOI: 10.3389/fpls.2022.819843 -
Biochimica Et Biophysica Acta Oct 2009Photosysthetic cleavage of water molecules to molecular oxygen is a crucial process for all aerobic life on the Earth. Light-driven oxidation of water occurs in... (Review)
Review
Photosysthetic cleavage of water molecules to molecular oxygen is a crucial process for all aerobic life on the Earth. Light-driven oxidation of water occurs in photosystem II (PSII) - a pigment-protein complex embedded in the thylakoid membrane of plants, algae and cyanobacteria. Electron transport across the thylakoid membrane terminated by NADPH and ATP formation is inadvertently coupled with the formation of reactive oxygen species (ROS). Reactive oxygen species are mainly produced by photosystem I; however, under certain circumstances, PSII contributes to the overall formation of ROS in the thylakoid membrane. Under limitation of electron transport reaction between both photosystems, photoreduction of molecular oxygen by the reducing side of PSII generates a superoxide anion radical, its dismutation to hydrogen peroxide and the subsequent formation of a hydroxyl radical terminates the overall process of ROS formation on the PSII electron acceptor side. On the PSII electron donor side, partial or complete inhibition of enzymatic activity of the water-splitting manganese complex is coupled with incomplete oxidation of water to hydrogen peroxide. The review points out the mechanistic aspects in the production of ROS on both the electron acceptor and electron donor side of PSII.
Topics: Electrons; Photosystem II Protein Complex; Reactive Oxygen Species
PubMed: 19463778
DOI: 10.1016/j.bbabio.2009.05.005 -
Frontiers in Plant Science 2019As a light-harvesting organelle, the chloroplast inevitably produces a substantial amount of reactive oxygen species (ROS) primarily through the photosystems. These ROS,... (Review)
Review
As a light-harvesting organelle, the chloroplast inevitably produces a substantial amount of reactive oxygen species (ROS) primarily through the photosystems. These ROS, such as superoxide anion, hydrogen peroxide, hydroxyl radical, and singlet oxygen, are potent oxidizing agents, thereby damaging the photosynthetic apparatus. On the other hand, it became increasingly clear that ROS act as beneficial tools under photo-oxidative stress conditions by stimulating chloroplast-nucleus communication, a process called retrograde signaling (RS). These ROS-mediated RS cascades appear to participate in a broad spectrum of plant physiology, such as acclimation, resistance, programmed cell death (PCD), and growth. Recent reports imply that ROS-driven oxidation of RS-associated components is essential in sensing and responding to an increase in ROS contents. ROS appear to activate RS pathways reversible or irreversible oxidation of sensor molecules. This review provides an overview of the emerging perspective on the topic of "oxidative modification-associated retrograde signaling."
PubMed: 32038693
DOI: 10.3389/fpls.2019.01729 -
International Journal of Molecular... Feb 2023The present study shows the effect of salinity on the functions of thylakoid membranes from two hybrid lines of : x and x , grown in a Hoagland solution with two NaCl...
Impact of Salinity on the Energy Transfer between Pigment-Protein Complexes in Photosynthetic Apparatus, Functions of the Oxygen-Evolving Complex and Photochemical Activities of Photosystem II and Photosystem I in Two Lines.
The present study shows the effect of salinity on the functions of thylakoid membranes from two hybrid lines of : x and x , grown in a Hoagland solution with two NaCl concentrations (100 and 150 mM) and different exposure times (10 and 25 days). We observed inhibition of the photochemical activities of photosystem I (DCPIH → MV) and photosystem II (HO → BQ) only after the short treatment (10 days) with the higher NaCl concentration. Data also revealed alterations in the energy transfer between pigment-protein complexes (fluorescence emission ratios F/F and FF), the kinetic parameters of the oxygen-evolving reactions (initial S-S state distribution, misses (α), double hits (β) and blocked centers (S)). Moreover, the experimental results showed that after prolonged treatment with NaCl x adapted to the higher concentration of NaCl (150 mM), while this concentration is lethal for x . This study demonstrated the relationship between the salt-induced inhibition of the photochemistry of both photosystems and the salt-induced changes in the energy transfer between the pigment-protein complexes and the alterations in the Mn cluster of the oxygen-evolving complex under salt stress.
Topics: Photosystem II Protein Complex; Thylakoids; Photosystem I Protein Complex; Salinity; Sodium Chloride; Photosynthesis; Energy Transfer; Oxygen; Chlorophyll
PubMed: 36834517
DOI: 10.3390/ijms24043108 -
Frontiers in Plant Science 2023Phycobilisomes serve as a light-harvesting antenna of both photosystem I (PSI) and II (PSII) in cyanobacteria, yet direct energy transfer from phycobilisomes to PSI is...
Phycobilisomes serve as a light-harvesting antenna of both photosystem I (PSI) and II (PSII) in cyanobacteria, yet direct energy transfer from phycobilisomes to PSI is not well documented. Here we recorded picosecond time-resolved fluorescence at wavelengths of 605-760 nm in isolated photosystem I (PSI), phycobilisomes and intact cells of a PSII-deficient mutant of sp. PCC 6803 at 77 K to study excitation energy transfer and trapping. By means of a simultaneous target analysis of the kinetics of isolated complexes and whole cells, the pathways and dynamics of energy transfer and were established. We establish that the timescale of the slowest equilibration between different terminal emitters in the phycobilisome is ≈800 ps. It was estimated that the terminal emitter in about 40% of the phycobilisomes transfers its energy with a rate constant of 42 ns to PSI. This energy transfer rate is higher than the rates of equilibration within the phycobilisome - between the rods and the core or between the core cylinders - and is evidence for the existence of specific phycobilisome-PSI interactions. The rest of the phycobilisomes remain unconnected or slowly transferring energy to PSI.
PubMed: 38078099
DOI: 10.3389/fpls.2023.1293813 -
Free Radical Biology & Medicine Aug 2019The ability to harvest light to drive chemical reactions and gain energy provided microbes access to high energy electron donors which fueled primary productivity,... (Review)
Review
The ability to harvest light to drive chemical reactions and gain energy provided microbes access to high energy electron donors which fueled primary productivity, biogeochemical cycles, and microbial evolution. Oxygenic photosynthesis is often cited as the most important microbial innovation-the emergence of oxygen-evolving photosynthesis, aided by geologic events, is credited with tipping the scale from a reducing early Earth to an oxygenated world that eventually lead to complex life. Anoxygenic photosynthesis predates oxygen-evolving photosynthesis and played a key role in developing and fine-tuning the photosystem architecture of modern oxygenic phototrophs. The release of oxygen as a by-product of metabolic activity would have caused oxidative damage to anaerobic microbiota that evolved under the anoxic, reducing conditions of early Earth. Photosynthetic machinery is particularly susceptible to the adverse effects of oxygen and reactive oxygen species and these effects are compounded by light. As a result, phototrophs employ additional detoxification mechanisms to mitigate oxidative stress and have evolved alternative oxygen-dependent enzymes for chlorophyll biosynthesis. Phylogenetic reconstruction studies and biochemical characterization suggest photosynthetic reactions centers, particularly in Cyanobacteria, evolved to both increase efficiency of electron transfer and avoid photodamage caused by chlorophyll radicals that is acute in the presence of oxygen. Here we review the oxygen and reactive oxygen species detoxification mechanisms observed in extant anoxygenic and oxygenic photosynthetic bacteria as well as the emergence of these mechanisms over evolutionary time. We examine the distribution of phototrophs in modern systems and phylogenetic reconstructions to evaluate the emergence of mechanisms to mediate oxidative damage and highlight changes in photosystems and reaction centers, chlorophyll biosynthesis, and niche space in response to oxygen production. This synthesis supports an emergence of HS-driven anoxygenic photosynthesis in Cyanobacteria prior to the evolution of oxygenic photosynthesis and underscores a role for the former metabolism in fueling fine-tuning of the oxygen evolving complex and mechanisms to repair oxidative damage. In contrast, we note the lack of elaborate mechanisms to deal with oxygen in non-cyanobacterial anoxygenic phototrophs suggesting these microbes have occupied similar niche space throughout Earth's history.
Topics: Biological Evolution; Cyanobacteria; Oxidation-Reduction; Oxygen; Photosynthesis; Phototrophic Processes
PubMed: 31078729
DOI: 10.1016/j.freeradbiomed.2019.05.003 -
Plant Signaling & Behavior Jan 2010Optimal photosynthetic performance requires that equal amounts of light are absorbed by photosystem II (PSII) and photosystem I (PSi), which are functionally linked... (Review)
Review
Optimal photosynthetic performance requires that equal amounts of light are absorbed by photosystem II (PSII) and photosystem I (PSi), which are functionally linked through the photosynthetic electron transport chain. However, photosynthetic organisms must cope with light conditions that lead to the preferential stimulation of one or the other of the photosystems. Plants react to such imbalances by mounting acclimation responses that redistribute excitation energy between photosystems and restore the photosynthetic redox poise. in the short term, this involves the so-called state transition process, which, over periods of minutes, alters the antennal cross-sections of the photosystems through the reversible association of a mobile fraction of light-harvesting complex II (LHCII) with PSI or PSII. Longer-lasting changes in light quality initiate a long-term response (LTr), occurring on a timescale of hours to days, that redresses imbalances in excitation energy by changing the relative amounts of the two photosystems. Despite the differences in their timescales of action, state transitions and LTr are both triggered by the redox state of the plastoquinone (PQ) pool, via the activation of the thylakoid kinase STN7, which appears to act as a common redox sensor and/or signal transducer for both responses. This review highlights recent findings concerning the role of STN7 in coordinating short- and long-term photosynthetic acclimation responses.
Topics: Acclimatization; Arabidopsis; Arabidopsis Proteins; Light; Oxidation-Reduction; Photosynthesis; Photosystem I Protein Complex; Photosystem II Protein Complex; Plastoquinone; Protein Kinases; Protein Serine-Threonine Kinases; Signal Transduction
PubMed: 20592803
DOI: 10.4161/psb.5.1.10198 -
Biochimica Et Biophysica Acta Aug 2011In oxygen-evolving photosynthesis, the two photosystems-photosystem I and photosystem II-function in parallel, and their excitation levels must be balanced to maintain... (Review)
Review
In oxygen-evolving photosynthesis, the two photosystems-photosystem I and photosystem II-function in parallel, and their excitation levels must be balanced to maintain an optimal photosynthetic rate under natural light conditions. State transitions in photosynthetic organisms balance the absorbed light energy between the two photosystems in a short time by relocating light-harvesting complex II proteins. For over a decade, the understanding of the physiological consequences, the molecular mechanism, and its regulation has increased considerably. After providing an overview of the general understanding of state transitions, this review focuses on the recent advances of the molecular aspects of state transitions with a particular emphasis on the studies using the green alga Chlamydomonas reinhardtii. This article is part of a Special Issue entitled: Regulation of Electron Transport in Chloroplasts.
Topics: Chloroplasts; Energy Metabolism; Models, Molecular; Photosynthesis; Photosystem I Protein Complex; Photosystem II Protein Complex
PubMed: 21108925
DOI: 10.1016/j.bbabio.2010.11.005 -
Life (Basel, Switzerland) Nov 2021The energetics of photosynthesis in plants have been re-analyzed in a framework that represents the relatively high energy of O correctly. Starting with the photon...
The energetics of photosynthesis in plants have been re-analyzed in a framework that represents the relatively high energy of O correctly. Starting with the photon energy exciting P680 and "loosening an electron", the energy transfer and electron transport are represented in a comprehensive, self-explanatory sequence of redox energy transfer and release diagrams. The resulting expanded Z-scheme explicitly shows charge separation as well as important high-energy species such as O, Tyr˙, and P680˙, whose energies are not apparent in the classical Z-scheme of photosynthesis. Crucially, the energetics of the three important forms of P680 and of P700 are clarified. The relative free energies of oxidized and reduced species are shown explicitly in kJ/mol, not encrypted in volts. Of the chemical energy produced in photosynthesis, more is stored in O than in glucose. The expanded Z-scheme introduced here provides explanatory power lacking in the classical scheme. It shows that P680* is energetically boosted to P680˙ by the favorable electron affinity of pheophytin and that Photosystem I (PSI) has insufficient energy to split HO and produce O because P700* is too easily ionized. It also avoids the Z-scheme's bewildering implication, according to the "electron waterfall" concept, that HO gives off electrons that spontaneously flow to chlorophyll while releasing energy. The new analysis explains convincingly why plants need two different photosystems in tandem: (i) PSII mostly extracts hydrogen from HO, producing PQH (plastoquinol), and generates the energetically expensive product O; this step provides little energy directly to the plant; (ii) PSI produces chemical energy for the organism, by pumping protons against a concentration gradient and producing less reluctant hydrogen donors. It also documents that electron transport and energy transfer occur in opposite directions and do not involve redox voltages. The analysis makes it clear that the high-energy species in photosynthesis are unstable, electron-deficient species such as P680˙ and Tyr˙, not putative high-energy electrons.
PubMed: 34833066
DOI: 10.3390/life11111191