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Plant Physiology Apr 2001With the aim to specifically study the molecular mechanisms behind photoinhibition of photosystem I, stacked spinach (Spinacia oleracea) thylakoids were irradiated at 4...
With the aim to specifically study the molecular mechanisms behind photoinhibition of photosystem I, stacked spinach (Spinacia oleracea) thylakoids were irradiated at 4 degrees C with far-red light (>715 nm) exciting photosystem I, but not photosystem II. Selective excitation of photosystem I by far-red light for 130 min resulted in a 40% inactivation of photosystem I. It is surprising that this treatment also caused up to 90% damage to photosystem II. This suggests that active oxygen produced at the reducing side of photosystem I is highly damaging to photosystem II. Only a small pool of the D1-protein was degraded. However, most of the D1-protein was modified to a slightly higher molecular mass, indicative of a damage-induced conformational change. The far-red illumination was also performed using destacked and randomized thylakoids in which the distance between the photosystems is shorter. Upon 130 min of illumination, photosystem I showed an approximate 40% inactivation as in stacked thylakoids. In contrast, photosystem II only showed 40% inactivation in destacked and randomized thylakoids, less than one-half of the inactivation observed using stacked thylakoids. In accordance with this, photosystem II, but not photosystem I is more protected from photoinhibition in destacked thylakoids. Addition of active oxygen scavengers during the far-red photosystem I illumination demonstrated superoxide to be a major cause of damage to photosystem I, whereas photosystem II was damaged mainly by superoxide and hydrogen peroxide.
Topics: Cell Fractionation; Chlorophyll; Chloroplasts; Darkness; Electron Transport; Guanosine Triphosphate; Light; Light-Harvesting Protein Complexes; Oxidation-Reduction; Oxygen; Photosynthetic Reaction Center Complex Proteins; Photosystem I Protein Complex; Photosystem II Protein Complex; Spinacia oleracea; Thylakoids
PubMed: 11299380
DOI: 10.1104/pp.125.4.2007 -
Photosynthesis Research Dec 1985In this review, the main research developments that have led to the current simplified picture of photosystem I are presented. This is followed by a discussion of some...
In this review, the main research developments that have led to the current simplified picture of photosystem I are presented. This is followed by a discussion of some conflicting reports and unresolved questions in the literature. The following points are made: (1) the evidence is contradictory on whether P700, the primary donor, is a monomer or dimer of chlorophyll although at this time the balacnce of the evidence points towards a monomeric structure for P700 when in the triplet state; (2) there is little evidence that the iron sulfur centers FA and FB act in series as tertiary acceptors and it is as likely that they act in parallel under physiological conditions; (3) a role for FX, probably another iron sulfur centrer, as an obligatory electron carrier in forward electron transfer has not been proven. Some evidence indicates that its reduction could represent a pathway different to that involving FA and FB; (4) the decay of the acceptor 'A2 (-)' as defined by optical spectroscopy corresponds with 700(+) % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOramaaBa% aaleaadaqdaaqaaiaadIfaaaaabeaaaaa!37D1!\[F_{\overline X } \] recombination under some circumstances but under other conditions it probably corresponds with P700(+) A1 (-) recombination; (5) P700(+) A1 (-) recombination as originally observed by optical spectroscopy is probably due to the decay of the P700 triplet state; (6) the acceptor A1 (-) as defined by EPR may be a special semiquinone molecule; (7) A0 is probably a chlorophyll a molecule which acts as the primary acceptor. Recombination of P700(+) A0 (-) gives rise to the P700 triplet state.A working model for electron transfer in photosystem I is presented, its general features are discussed and comparisons with other photosystems are made.
PubMed: 24442951
DOI: 10.1007/BF00054105 -
BBA Advances 2021Chlorophyll cofactors are vital for the metabolism of photosynthetic organisms. Cryo-electron microscopy (cryo-EM) has been used to elucidate molecular structures of...
Chlorophyll cofactors are vital for the metabolism of photosynthetic organisms. Cryo-electron microscopy (cryo-EM) has been used to elucidate molecular structures of pigment-protein complexes, but the minor structural differences between multiple types of chlorophylls make them difficult to distinguish in cryo-EM maps. This is exemplified by inconsistencies in the assignments of chlorophyll molecules in structures of photosystem I acclimated to far-red light (FRL-PSI). A quantitative assessment of chlorophyll substituents in cryo-EM maps was used to identify chlorophyll -binding sites in structures of FRL-PSI from two cyanobacteria. The two cryo-EM maps provide direct evidence for chlorophyll -binding at two and three binding sites, respectively, and three more sites in each structure exhibit strong indirect evidence for chlorophyll -binding. Common themes in chlorophyll -binding are described that clarify the current understanding of the molecular basis for FRL photoacclimation in photosystems.
PubMed: 37082022
DOI: 10.1016/j.bbadva.2021.100019 -
Photosynthesis Research Jun 2015When growth irradiance changes, phytoplankton acclimates by changing allocations to cellular components to re-balance their capacity to absorb photons versus their...
When growth irradiance changes, phytoplankton acclimates by changing allocations to cellular components to re-balance their capacity to absorb photons versus their capacity to use the electrons from the oxidation of water at photosystem II. Published changes in the cellular allocations resulting from photoacclimation across algal groups highlight that algae adopt different strategies. We examined the photoacclimation of the photosynthetic apparatus of six marine phytoplankters under near-natural diel irradiance patterns. For most of the phytoplankters, Chl a per structural photosystem II unit decreased with increasing growth irradiance, but a parallel decline in optical packaging effect allowed cells to maintain their functional absorption cross section serving active photosystem II units (σ PSII). Furthermore, no significant changes were observed in the ratio of Chl a per photosystem I. The diatom Skeletonema marinoi proved an exception to this pattern as Chl a per photosystem II is stable and Chl a per photosystem I slightly decreased with light intensity. A clear decrease in the photosystem content per cell was observed for all species except for Thalassiosira oceanica and S. marinoi. Rubisco content per cell showed little variation with irradiance for most algae, except for a 3-fold increase in S. marinoi. A ~700 % increase in the Rubisco:photosystem ratio across species with increasing growth irradiance indicates this is a key cellular stoichiometric adjustment to balance photon absorption capacity and the carbon reduction capacity. Increasing the Rubisco:photosystem ratio occurs through a decrease in the photosystems per cell for most of the phytoplankters in this study, except in the case of S. marinoi where Rubisco per cell increased.
Topics: Acclimatization; Chlorophyll; Chlorophyll A; Diatoms; Light; Photosystem I Protein Complex; Photosystem II Protein Complex; Phytoplankton; Ribulose-Bisphosphate Carboxylase
PubMed: 25862645
DOI: 10.1007/s11120-015-0137-6 -
Nature Apr 2023In oxygenic photosynthetic organisms, light energy is captured by antenna systems and transferred to photosystem II (PSII) and photosystem I (PSI) to drive...
In oxygenic photosynthetic organisms, light energy is captured by antenna systems and transferred to photosystem II (PSII) and photosystem I (PSI) to drive photosynthesis. The antenna systems of red algae consist of soluble phycobilisomes (PBSs) and transmembrane light-harvesting complexes (LHCs). Excitation energy transfer pathways from PBS to photosystems remain unclear owing to the lack of structural information. Here we present in situ structures of PBS-PSII-PSI-LHC megacomplexes from the red alga Porphyridium purpureum at near-atomic resolution using cryogenic electron tomography and in situ single-particle analysis, providing interaction details between PBS, PSII and PSI. The structures reveal several unidentified and incomplete proteins and their roles in the assembly of the megacomplex, as well as a huge and sophisticated pigment network. This work provides a solid structural basis for unravelling the mechanisms of PBS-PSII-PSI-LHC megacomplex assembly, efficient energy transfer from PBS to the two photosystems, and regulation of energy distribution between PSII and PSI.
Topics: Energy Transfer; Light-Harvesting Protein Complexes; Photosynthesis; Photosystem I Protein Complex; Photosystem II Protein Complex; Phycobilisomes; Porphyridium; Cryoelectron Microscopy; Single Molecule Imaging
PubMed: 36922595
DOI: 10.1038/s41586-023-05831-0 -
Plant Physiology Jun 1989The flash-induced electrochromic shift, measured by the amplitude of the rapid absorbance increase at 518 nanometers (DeltaA518), was used to determine the amount of...
The flash-induced electrochromic shift, measured by the amplitude of the rapid absorbance increase at 518 nanometers (DeltaA518), was used to determine the amount of charge separation within photosystems II and I in spinach (Spinacia oleracea L.) leaves. The recovery time of the reaction centers was determined by comparing the amplitudes of DeltaA518 induced by two flashes separated by a variable time interval. The recovery of the DeltaA518 on the second flash revealed that 20% of the reaction centers exhibited a recovery half-time of 1.7 +/- 0.3 seconds, which is 1000 times slower than normally active reaction centers. Measurements using isolated thylakoid membranes showed that photosystem I constituted 38% of the total number of reaction centers, and that the photosystem I reaction centers were nearly fully active, indicating that the slowly turning over reaction centers were due solely to photosystem II. The results demonstrate that in spinach leaves approximately 32% of the photosystem II complexes are effectively inactive, in that their contribution to energy conversion is negligible. Additional evidence for inactive photosystem II complexes in spinach leaves was provided by fluorescence induction measurements, used to monitor the oxidation kinetics of the primary quinone acceptor of photosystem II, Q(A), after a short flash. The measurements showed that in a fraction of the photosystem II complexes the oxidation of Q(A) (-) was slow, displaying a half-time of 1.5 +/- 0.3 seconds. The kinetics of Q(A) (-) oxidation were virtually identical to the kinetics of the recovery of photosystem II determined from the electrochromic shift. The key difference between active and inactive photosystem II centers is that in the inactive centers the oxidation rate of Q(A) (-) is slow compared to active centers. Measurements of the electrochromic shift in detached leaves from several different species of plants revealed a significant fraction of slowly turning over reaction centers, raising the possibility that reaction centers that are inefficient in energy conversion may be a common feature in plants.
PubMed: 16666841
DOI: 10.1104/pp.90.2.765 -
Annual Review of Plant Biology 2014Photosynthetic organisms are continuously subjected to changes in light quantity and quality, and must adjust their photosynthetic machinery so that it maintains optimal... (Review)
Review
Photosynthetic organisms are continuously subjected to changes in light quantity and quality, and must adjust their photosynthetic machinery so that it maintains optimal performance under limiting light and minimizes photodamage under excess light. To achieve this goal, these organisms use two main strategies in which light-harvesting complex II (LHCII), the light-harvesting system of photosystem II (PSII), plays a key role both for the collection of light energy and for photoprotection. The first is energy-dependent nonphotochemical quenching, whereby the high-light-induced proton gradient across the thylakoid membrane triggers a process in which excess excitation energy is harmlessly dissipated as heat. The second involves a redistribution of the mobile LHCII between the two photosystems in response to changes in the redox poise of the electron transport chain sensed through a signaling chain. These two processes strongly diminish the production of damaging reactive oxygen species, but photodamage of PSII is unavoidable, and it is repaired efficiently.
Topics: Light; Light-Harvesting Protein Complexes; Photosynthesis; Photosystem II Protein Complex; Plants; Signal Transduction; Thylakoids
PubMed: 24471838
DOI: 10.1146/annurev-arplant-050213-040226 -
Proceedings of the National Academy of... Mar 2007Proteorhodopsins (PRs) are retinal-containing proteins that catalyze light-activated proton efflux across the cell membrane. These photoproteins are known to be globally...
Proteorhodopsins (PRs) are retinal-containing proteins that catalyze light-activated proton efflux across the cell membrane. These photoproteins are known to be globally distributed in the ocean's photic zone, and they are found in a diverse array of Bacteria and Archaea. Recently, light-enhanced growth rates and yields have been reported in at least one PR-containing marine bacterium, but the physiological basis of light-activated growth stimulation has not yet been determined. To describe more fully PR photosystem genetics and biochemistry, we functionally surveyed a marine picoplankton large-insert genomic library for recombinant clones expressing PR photosystems in vivo. Our screening approach exploited transient increases in vector copy number that significantly enhanced the sensitivity of phenotypic detection. Two genetically distinct recombinants, initially identified by their orange pigmentation, expressed a small cluster of genes encoding a complete PR-based photosystem. Genetic and biochemical analyses of transposon mutants verified the function of gene products in the photopigment and opsin biosynthetic pathways. Heterologous expression of six genes, five encoding photopigment biosynthetic proteins and one encoding a PR, generated a fully functional PR photosystem that enabled photophosphorylation in recombinant Escherichia coli cells exposed to light. Our results demonstrate that a single genetic event can result in the acquisition of phototrophic capabilities in an otherwise chemoorganotrophic microorganism, and they explain in part the ubiquity of PR photosystems among diverse microbial taxa.
Topics: Adenosine Triphosphate; Archaeal Proteins; Bacterial Proteins; Cell Membrane; Escherichia coli; Gene Expression Regulation, Plant; Gene Library; Gene Transfer, Horizontal; Light; Models, Chemical; Models, Genetic; Molecular Sequence Data; Phosphorylation; Photosynthetic Reaction Center Complex Proteins; Rhodopsin; Rhodopsins, Microbial
PubMed: 17372221
DOI: 10.1073/pnas.0611470104 -
Current Protein & Peptide Science 2014Photosynthetic organisms and isolated photosystems are of interest for technical applications. In nature, photosynthetic electron transport has to work efficiently in... (Review)
Review
Photosynthetic organisms and isolated photosystems are of interest for technical applications. In nature, photosynthetic electron transport has to work efficiently in contrasting environments such as shade and full sunlight at noon. Photosynthetic electron transport is regulated on many levels, starting with the energy transfer processes in antenna and ending with how reducing power is ultimately partitioned. This review starts by explaining how light energy can be dissipated or distributed by the various mechanisms of non-photochemical quenching, including thermal dissipation and state transitions, and how these processes influence photoinhibition of photosystem II (PSII). Furthermore, we will highlight the importance of the various alternative electron transport pathways, including the use of oxygen as the terminal electron acceptor and cyclic flow around photosystem I (PSI), the latter which seem particularly relevant to preventing photoinhibition of photosystem I. The control of excitation pressure in combination with the partitioning of reducing power influences the light-dependent formation of reactive oxygen species in PSII and in PSI, which may be a very important consideration to any artificial photosynthetic system or technical device using photosynthetic organisms.
Topics: Electron Transport; Light; Photosynthesis; Photosystem I Protein Complex; Photosystem II Protein Complex; Reactive Oxygen Species
PubMed: 24678670
DOI: 10.2174/1389203715666140327105143 -
Nature Mar 2023Photosystems II and I (PSII, PSI) are the reaction centre-containing complexes driving the light reactions of photosynthesis; PSII performs light-driven water oxidation...
Photosystems II and I (PSII, PSI) are the reaction centre-containing complexes driving the light reactions of photosynthesis; PSII performs light-driven water oxidation and PSI further photo-energizes harvested electrons. The impressive efficiencies of the photosystems have motivated extensive biological, artificial and biohybrid approaches to 're-wire' photosynthesis for higher biomass-conversion efficiencies and new reaction pathways, such as H evolution or CO fixation. Previous approaches focused on charge extraction at terminal electron acceptors of the photosystems. Electron extraction at earlier steps, perhaps immediately from photoexcited reaction centres, would enable greater thermodynamic gains; however, this was believed impossible with reaction centres buried at least 4 nm within the photosystems. Here, we demonstrate, using in vivo ultrafast transient absorption (TA) spectroscopy, extraction of electrons directly from photoexcited PSI and PSII at early points (several picoseconds post-photo-excitation) with live cyanobacterial cells or isolated photosystems, and exogenous electron mediators such as 2,6-dichloro-1,4-benzoquinone (DCBQ) and methyl viologen. We postulate that these mediators oxidize peripheral chlorophyll pigments participating in highly delocalized charge-transfer states after initial photo-excitation. Our results challenge previous models that the photoexcited reaction centres are insulated within the photosystem protein scaffold, opening new avenues to study and re-wire photosynthesis for biotechnologies and semi-artificial photosynthesis.
Topics: Chlorophyll; Oxidation-Reduction; Photosynthesis; Photosystem I Protein Complex; Photosystem II Protein Complex; Time Factors; Carbon Cycle; Carbon Dioxide; Hydrogen; Cyanobacteria; Electrons; Thermodynamics
PubMed: 36949188
DOI: 10.1038/s41586-023-05763-9