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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 -
Biochimica Et Biophysica Acta Sep 2014Cyanobacteria have multiple psbA genes encoding PsbA, the D1 reaction center protein of the Photosystem II complex which bears together with PsbD, the D2 protein, most... (Review)
Review
Cyanobacteria have multiple psbA genes encoding PsbA, the D1 reaction center protein of the Photosystem II complex which bears together with PsbD, the D2 protein, most of the cofactors involved in electron transfer reactions. The thermophilic cyanobacterium Thermosynechococcus elongatus has three psbA genes differently expressed depending on the environmental conditions. Among the 344 residues constituting each of the 3 possible PsbA variants there are 21 substitutions between PsbA1 and PsbA3, 31 between PsbA1 and PsbA2 and 27 between PsbA2 and PsbA3. In this review, we summarize the changes already identified in the properties of the redox cofactors depending on the D1 variant constituting Photosystem II in T. elongatus. This article is part of a special issue entitled: photosynthesis research for sustainability: keys to produce clean energy.
Topics: Amino Acid Sequence; Cyanobacteria; Electron Transport; Light; Molecular Sequence Data; Photosystem II Protein Complex; Quinones
PubMed: 24388918
DOI: 10.1016/j.bbabio.2013.12.011 -
PloS One 2017The marine picocyanobacteria Synechococcus and Prochlorococcus numerically dominate open ocean phytoplankton. Although evolutionarily related they are ecologically...
The marine picocyanobacteria Synechococcus and Prochlorococcus numerically dominate open ocean phytoplankton. Although evolutionarily related they are ecologically distinct, with different strategies to harvest, manage and exploit light. We grew representative strains of Synechococcus and Prochlorococcus and tracked their susceptibility to photoinactivation of Photosystem II under a range of light levels. As expected blue light provoked more rapid photoinactivation than did an equivalent level of red light. The previous growth light level altered the susceptibility of Synechococcus, but not Prochlorococcus, to this photoinactivation. We resolved a simple linear pattern when we expressed the yield of photoinactivation on the basis of photons delivered to Photosystem II photochemistry, plotted versus excitation pressure upon Photosystem II, the balance between excitation and downstream metabolism. A high excitation pressure increases the generation of reactive oxygen species, and thus increases the yield of photoinactivation of Photosystem II. Blue photons, however, retained a higher baseline photoinactivation across a wide range of excitation pressures. Our experiments thus uncovered the relative influences of the direct photoinactivation of Photosystem II by blue photons which dominates under low to moderate blue light, and photoinactivation as a side effect of reactive oxygen species which dominates under higher excitation pressure. Synechococcus enjoyed a positive metabolic return upon the repair or the synthesis of a Photosystem II, across the range of light levels we tested. In contrast Prochlorococcus only enjoyed a positive return upon synthesis of a Photosystem II up to 400 μmol photons m-2 s-1. These differential cost-benefits probably underlie the distinct photoacclimation strategies of the species.
Topics: Light; Photons; Photosynthesis; Photosystem II Protein Complex; Plant Leaves; Prochlorococcus; Reactive Oxygen Species; Synechococcus
PubMed: 28129341
DOI: 10.1371/journal.pone.0168991 -
Nature Communications Jun 2024Cryptophytes are ancestral photosynthetic organisms evolved from red algae through secondary endosymbiosis. They have developed alloxanthin-chlorophyll a/c2-binding...
Cryptophytes are ancestral photosynthetic organisms evolved from red algae through secondary endosymbiosis. They have developed alloxanthin-chlorophyll a/c2-binding proteins (ACPs) as light-harvesting complexes (LHCs). The distinctive properties of cryptophytes contribute to efficient oxygenic photosynthesis and underscore the evolutionary relationships of red-lineage plastids. Here we present the cryo-electron microscopy structure of the Photosystem II (PSII)-ACPII supercomplex from the cryptophyte Chroomonas placoidea. The structure includes a PSII dimer and twelve ACPII monomers forming four linear trimers. These trimers structurally resemble red algae LHCs and cryptophyte ACPI trimers that associate with Photosystem I (PSI), suggesting their close evolutionary links. We also determine a Chl a-binding subunit, Psb-γ, essential for stabilizing PSII-ACPII association. Furthermore, computational calculation provides insights into the excitation energy transfer pathways. Our study lays a solid structural foundation for understanding the light-energy capture and transfer in cryptophyte PSII-ACPII, evolutionary variations in PSII-LHCII, and the origin of red-lineage LHCIIs.
Topics: Photosystem II Protein Complex; Light-Harvesting Protein Complexes; Cryptophyta; Cryoelectron Microscopy; Photosynthesis; Models, Molecular; Energy Transfer; Photosystem I Protein Complex; Chlorophyll A
PubMed: 38866834
DOI: 10.1038/s41467-024-49453-0 -
Biochimica Et Biophysica Acta.... Feb 2020Hetero-oligomeric membrane protein complexes form the electron transport chain (ETC) of oxygenic photosynthesis. The ETC complexes undertake the light-driven vectorial...
Hetero-oligomeric membrane protein complexes form the electron transport chain (ETC) of oxygenic photosynthesis. The ETC complexes undertake the light-driven vectorial electron and proton transport reactions, which generate energy-rich ATP and electron-rich NADPH molecules for carbon fixation. The rate of photosynthetic electron transport depends on the availability of photons and the relative abundance of electron transport complexes. The relative abundance of the two photosystems, critical for the quantum efficiency of photosynthesis in changing light quality conditions, has been determined successfully by optical methods. Due to the lack of spectroscopic signatures, however, relatively little is known about the stoichiometry of other non-photosystem complexes in plant photosynthetic membrane. Here we determine the ratios of all major thylakoid-bound ETC complexes in Arabidopsis by a label-free quantitative mass spectrometry technique. The calculated stoichiometries are consistent with known subunit composition of complexes and current estimates of photosystem and cytochrome bf concentrations. The implications of these stoichiometries for photosynthetic light harvesting and the partitioning of electrons between the linear and cyclic electron transport pathways of photosynthesis are discussed.
Topics: Arabidopsis; Arabidopsis Proteins; Cytochrome b6f Complex; Photosynthesis; Thylakoids
PubMed: 31825808
DOI: 10.1016/j.bbabio.2019.148141 -
Plants (Basel, Switzerland) Sep 2022Clary sage ( L.) is a medicinal plant that has the potential to be used for phytoextraction of zinc (Zn) and cadmium (Cd) from contaminated soils by accumulating these...
Combined Impact of Excess Zinc and Cadmium on Elemental Uptake, Leaf Anatomy and Pigments, Antioxidant Capacity, and Function of Photosynthetic Apparatus in Clary Sage ( L.).
Clary sage ( L.) is a medicinal plant that has the potential to be used for phytoextraction of zinc (Zn) and cadmium (Cd) from contaminated soils by accumulating these metals in its tissues. Additionally, it has been found to be more tolerant to excess Zn than to Cd stress alone; however, the interactive effects of the combined treatment with Zn and Cd on this medicinal herb, and the protective strategies of Zn to alleviate Cd toxicity have not yet been established in detail. In this study, clary sage plants grown hydroponically were simultaneously exposed to Zn (900 µM) and Cd (100 μM) for 8 days to obtain more detailed information about the plant responses and the role of excess Zn in mitigating Cd toxicity symptoms. The leaf anatomy, photosynthetic pigments, total phenolic and anthocyanin contents, antioxidant capacity (by DPPH and FRAP analyses), and the uptake and distribution of essential elements were investigated. The results showed that co-exposure to Zn and Cd leads to an increased leaf content of Fe and Mg compared to the control, and to increased leaf Ca, Mn, and Cu contents compared to plants treated with Cd only. This is most likely involved in the defense mechanisms of excess Zn against Cd toxicity to protect the chlorophyll content and the functions of both photosystems and the oxygen-evolving complex. The data also revealed that the leaves of clary sage plants subjected to the combined treatment have an increased antioxidant capacity attributed to the higher content of polyphenolic compounds. Furthermore, light microscopy indicated more alterations in the leaf morphology after Cd-only treatment than after the combined treatment. The present study shows that excess Zn could mitigate Cd toxicity in clary sage plants.
PubMed: 36145808
DOI: 10.3390/plants11182407 -
Archives of Microbiology Feb 2022This investigation tested the hypothesis that the native cyanobacteria can acclimatize and grow under the combination of environmental factors and/or how does their...
This investigation tested the hypothesis that the native cyanobacteria can acclimatize and grow under the combination of environmental factors and/or how does their process change with the age of culture? Here, we tried to combine multiple factors to simulated what happens in natural ecosystems. We analyzed the physiological response of terrestrial cyanobacterium, Cylindrospermum sp. FS 64 under combination effect of different salinity (17, 80, and 160 mM) and alkaline pHs (9 and 11) at extremely limited carbon dioxide concentration (no aeration) up to 96 h. Our evidence showed that growth, biomass, photosystem II, and phycobilisome activity significantly increased under 80 mM salinity and pH 11. In addition, this combined condition led to a significant increase in maximum light-saturated photosynthesis activity and photosynthetic efficiency. While phycobilisomes and photosystem activity decreased by increasing salinity (160 mM) which caused decreased growth rates after 96 h. The single-cell study (CLMS microscopy) which illustrated the physiological state of the individual and active-cell confirmed the efficiency and effectiveness of both photosystems and phycobilisome under the combined effect of 80 mM salinity and pH 11.
Topics: Acclimatization; Cyanobacteria; Ecosystem; Light; Photosynthesis; Phycobilisomes
PubMed: 35122519
DOI: 10.1007/s00203-022-02772-6 -
Science (New York, N.Y.) Jun 2018Photosystems I and II convert solar energy into the chemical energy that powers life. Chlorophyll a photochemistry, using red light (680 to 700 nm), is near universal...
Photosystems I and II convert solar energy into the chemical energy that powers life. Chlorophyll a photochemistry, using red light (680 to 700 nm), is near universal and is considered to define the energy "red limit" of oxygenic photosynthesis. We present biophysical studies on the photosystems from a cyanobacterium grown in far-red light (750 nm). The few long-wavelength chlorophylls present are well resolved from each other and from the majority pigment, chlorophyll a. Charge separation in photosystem I and II uses chlorophyll f at 745 nm and chlorophyll f (or d) at 727 nm, respectively. Each photosystem has a few even longer-wavelength chlorophylls f that collect light and pass excitation energy uphill to the photochemically active pigments. These photosystems function beyond the red limit using far-red pigments in only a few key positions.
Topics: Chlorophyll; Chlorophyll A; Cyanobacteria; Light; Photosynthesis; Photosystem I Protein Complex; Photosystem II Protein Complex
PubMed: 29903971
DOI: 10.1126/science.aar8313 -
Biochimica Et Biophysica Acta Sep 2015Photosystem (PS) II is a multisubunit thylakoid membrane pigment-protein complex responsible for light-driven oxidation of water and reduction of plastoquinone.... (Review)
Review
Photosystem (PS) II is a multisubunit thylakoid membrane pigment-protein complex responsible for light-driven oxidation of water and reduction of plastoquinone. Currently more than 40 proteins are known to associate with PSII, either stably or transiently. The inherent feature of the PSII complex is its vulnerability in light, with the damage mainly targeted to one of its core proteins, the D1 protein. The repair of the damaged D1 protein, i.e. the repair cycle of PSII, initiates in the grana stacks where the damage generally takes place, but subsequently continues in non-appressed thylakoid domains, where many steps are common for both the repair and de novo assembly of PSII. The sequence of the (re)assembly steps of genuine PSII subunits is relatively well-characterized in higher plants. A number of novel findings have shed light into the regulation mechanisms of lateral migration of PSII subcomplexes and the repair as well as the (re)assembly of the complex. Besides the utmost importance of the PSII repair cycle for the maintenance of PSII functionality, recent research has pointed out that the maintenance of PSI is closely dependent on regulation of the PSII repair cycle. This review focuses on the current knowledge of regulation of the repair cycle of PSII in higher plant chloroplasts. Particular emphasis is paid on sequential assembly steps of PSII and the function of the number of PSII auxiliary proteins involved both in the biogenesis and repair of PSII. This article is part of a Special Issue entitled: Chloroplast Biogenesis.
Topics: Chloroplasts; Phosphorylation; Photosystem II Protein Complex; Protein Transport
PubMed: 25615587
DOI: 10.1016/j.bbabio.2015.01.006 -
The Plant Journal : For Cell and... Mar 2019Natural growth environments commonly include fluctuating conditions that can disrupt the photosynthetic energy balance and induce photoinhibition through inactivation of...
Natural growth environments commonly include fluctuating conditions that can disrupt the photosynthetic energy balance and induce photoinhibition through inactivation of the photosynthetic apparatus. Photosystem II (PSII) photoinhibition is efficiently reversed by the PSII repair cycle, whereas photoinhibited photosystem I (PSI) recovers much more slowly. In the current study, treatment of the Arabidopsis thaliana mutant proton gradient regulation 5 (pgr5) with excess light was used to compromise PSI functionality in order to investigate the impact of photoinhibition and subsequent recovery on photosynthesis and carbon metabolism. The negative impact of PSI photoinhibition on CO fixation was especially deleterious under low irradiance. Impaired starch accumulation after PSI photoinhibition was reflected in reduced respiration in the dark, but this was not attributed to impaired sugar synthesis. Normal chloroplast and mitochondrial metabolisms were shown to recover despite the persistence of substantial PSI photoinhibition for several days. The results of this study indicate that the recovery of PSI function involves the reorganization of the light-harvesting antennae, and suggest a pool of surplus PSI that can be recruited to support photosynthesis under demanding conditions.
Topics: Arabidopsis; Arabidopsis Proteins; Carbohydrate Metabolism; Carbon; Carbon Dioxide; Chloroplasts; Light; Mitochondria; Mutation; Photosynthesis; Photosynthetic Reaction Center Complex Proteins; Photosystem I Protein Complex; Photosystem II Protein Complex; Starch
PubMed: 30488561
DOI: 10.1111/tpj.14177