Electron Transfer In Photosynthesis Research Articles

Cadmium-Induced Physiological Responses, Biosorption and Bioaccumulation in Scenedesmus obliquus.

Cadmium ion (Cd2+) is a highly toxic metal in water, even at low concentrations. Microalgae are a promising material for heavy metal remediation. The present study investigated the effects of Cd2+ on growth, photosynthesis, antioxidant enzyme activities, cell morphology, and Cd2+ adsorption and accumulation capacity of the freshwater green alga Scenedesmus obliquus. Experiments were conducted by exposing S. obliquus to varying concentrations of Cd2+ for 96 h, assessing its tolerance and removal capacity towards Cd2+. The results showed that higher concentrations of Cd2+ (>0.5 mg L-1) reduced pigment content, inhibited algal growth and electron transfer in photosynthesis, and led to morphological changes such as mitochondrial disappearance and chloroplast deformation. In this process, S. obliquus counteracted Cd2+ toxicity by enhancing antioxidant enzyme activities, accumulating starch and high-density granules, and secreting extracellular polymeric substances. When the initial Cd2+ concentration was less than or equal to 0.5 mg L-1, S. obliquus was able to efficiently remove over 95% of Cd2+ from the environment through biosorption and bioaccumulation. However, when the initial Cd2+ concentration exceeded 0.5 mg L-1, the removal efficiency decreased slightly to about 70%, with biosorption accounting for more than 60% of this process, emerging as the predominant mechanism for Cd2+ removal. Fourier transform infrared correlation spectroscopy analysis indicated that the carboxyl and amino groups of the cell wall were the key factors in removing Cd2+. In conclusion, S. obliquus has considerable potential for the remediation of aquatic environments with Cd2+, providing algal resources for developing new microalgae-based bioremediation techniques for heavy metals.

Mutation in Mg-Protoporphyrin IX Monomethyl Ester (Oxidative) Cyclase Gene ZmCRD1 Causes Chlorophyll-Deficiency in Maize.

Chlorophyll molecules are non-covalently associated with chlorophyll-binding proteins to harvest light and perform charge separation vital for energy conservation during photosynthetic electron transfer in photosynthesis for photosynthetic organisms. The present study characterized a pale-green leaf (pgl) maize mutant controlled by a single recessive gene causing chlorophyll reduction throughout the whole life cycle. Through positional mapping and complementation allelic test, Zm00001d008230 (ZmCRD1) with two missense mutations (p.A44T and p.T326M) was identified as the causal gene encoding magnesium-protoporphyrin IX monomethyl ester cyclase (MgPEC). Phylogenetic analysis of ZmCRD1 within and among species revealed that the p.T326M mutation was more likely to be causal. Subcellular localization showed that ZmCRD1 was targeted to chloroplasts. The pgl mutant showed a malformed chloroplast morphology and reduced number of starch grains in bundle sheath cells. The ZmCRD1 gene was mainly expressed in WT and mutant leaves, but the expression was reduced in the mutant. Most of the genes involved in chlorophyll biosynthesis, chlorophyll degradation, chloroplast development and photosynthesis were down-regulated in pgl. The photosynthetic capacity was limited along with developmental retardation and production reduction in pgl. These results confirmed the crucial role of ZmCRD1 in chlorophyll biosynthesis, chloroplast development and photosynthesis in maize.

Structure of a tetrameric photosystem I from a glaucophyte alga Cyanophora paradoxa

Photosystem I (PSI) is one of the two photosystems functioning in light-energy harvesting, transfer, and electron transfer in photosynthesis. However, the oligomerization state of PSI is variable among photosynthetic organisms. We present a 3.8-Å resolution cryo-electron microscopic structure of tetrameric PSI isolated from the glaucophyte alga Cyanophora paradoxa, which reveals differences with PSI from other organisms in subunit composition and organization. The PSI tetramer is organized in a dimer of dimers with a C2 symmetry. Unlike cyanobacterial PSI tetramers, two of the four monomers are rotated around 90°, resulting in a completely different pattern of monomer-monomer interactions. Excitation-energy transfer among chlorophylls differs significantly between Cyanophora and cyanobacterial PSI tetramers. These structural and spectroscopic features reveal characteristic interactions and excitation-energy transfer in the Cyanophora PSI tetramer, suggesting that the Cyanophora PSI could represent a turning point in the evolution of PSI from prokaryotes to eukaryotes.

6-Ethoxy-4- N-(2-morpholin-4-ylethyl) -2-N-propan-2-yl-1,3, 5-triazine-2, 4-diamineendows herbicidal activity against Phalaris minora weed of wheat crop field: An in -silico and experimental approaches of herbicide discovery.

Phalaris minor is a major weed of wheat crop which has evolved resistance against herbicides. Isoproturon is the most accepted herbicide developedresistance in 1992. Later, introduced herbicides also developed resistance and cross-resistance to their respective binding sites. Isoproturon binds at the QB binding site of the D1 protein of photosystem-II (PS-II), which blocks the electron transfer in photosynthesis. In this work, we have carried out a series of computational studies to prioritize the promising herbicides against D1 protein of P. minor. Through the computational studies, twenty-four lead molecules are prioritized which have shown a higher binding affinity and inhibition constant than the reference ligand molecule. The binding and conformational stability of docked complexes was evaluated by molecular dynamics simulations and binding free energy calculations i.e., MM/PBSA. A list of amino acids such as Ala225, Ser226, Phe227, and Asn229 present in the binding site of protein is obtained to be playing an important role in the stability of the protein-lead complex via hydrogen bond and π-π interactions. Binding free energy calculation revealed that the selected lead molecule binding is energetically favorable and driven by electrostatic interactions. Among 24 leads, computational results have uncovered eight promising compounds as potential herbicides which have shown comparable physiochemical profile, better docking scores, system stability, H-bond occupancy, and binding free energy than terbutryn, a reference molecule. These prioritized molecules were custom synthesized and evaluated for their herbicidal activity and specificity through whole plant assay under laboratory-controlled conditions. The lead molecule ELC5 (6-ethoxy-4-N-(2-morpholin-4-ylethyl)-2-N-propan-2-yl-1,3,5-triazine-2,4-diamine) has shown comparable activity to the reference herbicide(isoproturon) against P. minor.

Delayed fluorescence as a new screening method of plant species for urban greening: an experimental study using four bryophytes

Selecting suitable plant species is important in urban greening because urban environments often provide unfavorable conditions for plant growth. We focused on delayed fluorescence (DF), i.e., light emitted from plants immediately following light exposure as a result of back electron transfer in photosynthesis, as an indicator of photosynthetic activity. Moss greening, urban greening using bryophytes, has attracted attention as a new domain of greening that does not require soil. Therefore, tolerance to drying, which is a characteristic environmental factor in cities, of four bryophytes—Bryum argenteum Hedw., Racomitrium japonicum Dozy et Molk., Hypnum plumaeforme Wilson, and Polytrichum commune Hedw.—was evaluated in the laboratory using DF. Assuming an urban environment, experiments were performed to measure the transition of DF following the cessation of irrigation and re-watering. The recovery of accumulated DF values (0–200 s) by rehydration 8 days after irrigation cessation was increased in the order H. plumaeforme ≈ P. commune < R. japonicum < B. argenteum. B. argenteum presented an increase in the accumulated amount of DF 8 h after irrigation cessation, and presented a significantly higher DF when compared with the other three species at 16 h. Together with results of previous studies, these findings of desiccation tolerance in the studied species indicate that DF is a useful method for characterizing desiccation tolerance in plants and selecting potentially useful plants for urban greening.

Investigations on The Mechanism of Artificial Photosynthesis of Ca-Pc-PDI and Dendrimer Molecule by DFT Calculations

Artificial photosynthesis modelling of Ca-Pc-PDI complex Ca Phthalocyanine Perylenediimide), and dendrimer molecule using Density of Functional Theory (DFT) Method has been studied to showed the energy efficiency of these compounds in terms of electron transfer in photosynthesis. The Analysis of Ca-Pc-PDI and dendrimer compound and also chlorophyl has been done in all computations using the GAMESS-US software. The computations result in this research showed that the large wavelength complex compounds of Ca-Pc-PDI obtained was 138.3299 nm and energy efficiency obtained was 0.89 eV. The data analysis states that the absorption of harvest light energy of complex compounds Ca-Pc-PDI lies in the far UV spectrum. The other side, the polyphenylene dendrimer structure molecular orbital analyses it was found that the dendrimer was capable of electron transfers as indicated by the existence of HOMO and LUMO and result comparisons with chlorophyll. UV wavelengths of the polyethylene dendrimer and chlorophyll, respectively, suggesting that the polyphenylene dendrimer is capable of substituting chlorophyll in artificial photosyntheses. We can states from the result that these compound ability to be applied in the modeling of artificial photosynthesis as a material of energy absorption that mimics the workings of chlorophyll in terms of electron transfer in natural photosynthesis process. Keywords: Artificial photosynthesis modelling, Ca-Phthalocyanine-Perylenediimide complex, and dendrimer molecule

Effect of copper contaminated food on the life cycle and secondary production of Daphnia laevis

In aquatic environments, copper (Cu) plays important physiological roles in planktonic food chain, such as electron transfer in photosynthesis and constituting proteins that transport oxygen in some arthropods, while at higher concentrations it is toxic on these organisms and higher trophic levels. The combined effects of natural (e.g. volcanic activity) and anthropogenic sources (e.g. mining waste) contribute to the increase in copper pollution in different ecosystems and regions around the world. In the present study, we evaluated the bioaccumulation and effect of Cu on Raphidocelis subcapitata (freshwater algae), and the influence of Cu-contaminated food (algae) on Daphnia laevis (tropical cladoceran). The amount of copper accumulated in microalgae and cladoceran was quantified, and life-history parameters of D. laevis such as growth, reproduction and longevity were measured. The cell density of Cu exposed R. subcapitata declined, and cladoceran fed with contaminated food had lower longevity, production of eggs and neonates, and reduced secondary production. A concentration dependent increase in Cu accumulation was observed in the microalgae, while the opposite occurred in the animal, indicating a cellular metal regulatory mechanism in the latter. However, this regulation seems not to be sufficient to avoid metal induced damages in the cladoceran such as decreased longevity and reproduction. We conclude that diet is an important metal exposure route to this cladoceran, and the assessment of chronic contamination during the complete life cycle of cladoceran provides results that are similar to those observed in natural environments, especially when native organisms are investigated.

Plasticity of bud phenology and photosynthetic capacity in hybrid poplar plantations along a latitudinal gradient in northeastern Canada

Intensively managed plantations are being established in a wide range of environmental conditions to satisfy the high demand for wood products and reduce the exploitation pressure on natural forests. In this study, we investigated the plasticity of four hybrid poplar (Populus spp.) clones established in 2005 along a latitudinal gradient in northwestern Quebec, Canada. The effect of latitudinal gradient on maximum rates of electron transfer (Jmax) and carboxylation (Vcmax), dark respiration (Rd), spring and fall bud phenology, net photosynthesis (Pn), specific leaf area (SLA), per mass nitrogen leaf concentration (Nm) were assessed in order to evaluate if clonal plasticity would result in increased overall productivity.Growth season duration between the southernmost to the northernmost sites ranged 21–32 days, and was positively correlated to stem volume and negatively correlated to bud burst and bud set duration. Growth increment (stem volume) along the latitudinal gradient ranged 100–184% between the least and most productive clone. Clone 747215 had the most stable but the slowest growth. Leaf net photosynthesis decreased or did not change northwards except for the most productive clone for which it increased slightly likely due to a significant decrease in SLA. Maximum rates of carboxylation and photosynthesis electron transfer (Vcmax and Jmax) decreased northwards for three of the four clones, suggesting that photosynthesis of trees did not acclimate to lower temperatures from south to north. Plasticity of photosynthetic variables, measured with trait plasticity index was usually greater than that of SLA and Nm.

Cell size and the blockage of electron transfer in photosynthesis: Proposed endpoints for algal assays and its application to soil alga Chlorococcum infusionum

This study evaluated multiple endpoints of algal assays to identify sensitive and easy to use endpoints that could be applied to evaluate algal toxicity in metal-polluted soil extracts. Soil algae play an important role in trophic levels; thus, Chlorococcum infusionum was selected as the test species. Soil extracts were used because they might help identify potential soil retention and ecological hazards caused by pollutants that are present in the soil aqueous phase. The multi-endpoints measured were growth yield, photosynthetic activities, and cell viabilities. Nine parameters were measured to evaluate photosynthetic activity; namely, specific energy fluxes per quinone A-reducing photosystem II reaction center (absorption flux, trapped energy flux, electron transport flux, and dissipated energy flux per reaction center), quantum yields (maximum quantum yield of primary photochemistry, quantum yield of electron transport, quantum yield of energy dissipation, and average quantum yield of primary photochemistry), and the blockage of electron transfer from the reaction center to the quinone pool. Cell viability was evaluated by measuring cell size, cell granularity, and the autofluorescence of chlorophyll using flow cytometry. The results showed that heavy metals reduced growth yield, cell viability, and the photosynthetic activity of C. infusionum in soil extracts. Out of the 13 tested endpoints, the blockage of electron transfer from the reaction center to the quinone pool and cell size represented the most sensitive endpoints. We propose that both endpoints should be measured, along with conventional growth yield, to determine the effect of soil pollutants and to lower pollutant concentrations in soils.

Revisiting the Supramolecular Organization of Photosystem II in Chlamydomonas reinhardtii

Photosystem II (PSII) is a multiprotein complex that splits water and initiates electron transfer in photosynthesis. The central part of PSII, the PSII core, is surrounded by light-harvesting complex II proteins (LHCIIs). In higher plants, two or three LHCII trimers are seen on each side of the PSII core whereas only one is seen in the corresponding positions in Chlamydomonas reinhardtii, probably due to the absence of CP24, a minor monomeric LHCII. Here, we re-examined the supramolecular organization of the C. reinhardtii PSII-LHCII supercomplex by determining the effect of different solubilizing detergents. When we solubilized the thylakoid membranes with n-dodecyl-β-D-maltoside (β-DM) or n-dodecyl-α-D-maltoside (α-DM) and subjected them to gel filtration, we observed a clear difference in molecular mass. The α-DM-solubilized PSII-LHCII supercomplex bound twice more LHCII than the β-DM-solubilized supercomplex and retained higher oxygen-evolving activity. Single-particle image analysis from electron micrographs of the α-DM-solubilized and negatively stained supercomplex revealed that the PSII-LHCII supercomplex had a novel supramolecular organization, with three LHCII trimers attached to each side of the core.

Spectroscopic evidence for the effect of the ortho H2O spin on the electron transfer in photosynthesis

A spin mechanism for electron transfer control in the reaction center of purple bacteria in photosynthesis is proposed. Rotation and conversion of the ortho/para spin isomers of two H2O molecules located near the special pair of the reaction center are treated as the sources of the coherent modulations of transient kinetics. Modulation of the collective wave function of the reaction center electrons by the total proton spin of ortho H2O is a key feature allowing the molecule to play the role of a gate controlling the electron transfer. The iron atom in the reaction center with the gradient magnetic field is treated as a catalyst removing the strict forbiddenness of H2O ortho/para conversion. It is shown that the modulation of the reaction center stimulated emission kinetics observed in the field of femtosecond pulses coincides with the rotational transitions of ortho/para H2O. Influence of the effect of the electric field (Stark effect) on the level displacement and ortho/para conversion rate is discussed.

Carboxylate Shifts Steer Interquinone Electron Transfer in Photosynthesis

Understanding the mechanisms of electron transfer (ET) in photosynthetic reaction centers (RCs) may inspire novel catalysts for sunlight-driven fuel production. The electron exit pathway of type II RCs comprises two quinone molecules working in series and in between a non-heme iron atom with a carboxyl ligand (bicarbonate in photosystem II (PSII), glutamate in bacterial RCs). For decades, the functional role of the iron has remained enigmatic. We tracked the iron site using microsecond-resolution x-ray absorption spectroscopy after laser-flash excitation of PSII. After formation of the reduced primary quinone, Q(A)(-), the x-ray spectral changes revealed a transition (t½ ≈ 150 μs) from a bidentate to a monodentate coordination of the bicarbonate at the Fe(II) (carboxylate shift), which reverted concomitantly with the slower ET to the secondary quinone Q(B). A redox change of the iron during the ET was excluded. Density-functional theory calculations corroborated the carboxylate shift both in PSII and bacterial RCs and disclosed underlying changes in electronic configuration. We propose that the iron-carboxyl complex facilitates the first interquinone ET by optimizing charge distribution and hydrogen bonding within the Q(A)FeQ(B) triad for high yield Q(B) reduction. Formation of a specific priming intermediate by nuclear rearrangements, setting the stage for subsequent ET, may be a common motif in reactions of biological redox cofactors.

Rationally tuning the reduction potential of a single cupredoxin beyond the natural range

Redox processes are at the heart of numerous functions in chemistry and biology, from long-range electron transfer in photosynthesis and respiration to catalysis in industrial and fuel cell research. These functions are accomplished in nature by only a limited number of redox-active agents. A long-standing issue in these fields is how redox potentials are fine-tuned over a broad range with little change to the redox-active site or electron-transfer properties. Resolving this issue will not only advance our fundamental understanding of the roles of long-range, non-covalent interactions in redox processes, but also allow for design of redox-active proteins having tailor-made redox potentials for applications such as artificial photosynthetic centres or fuel cell catalysts for energy conversion. Here we show that two important secondary coordination sphere interactions, hydrophobicity and hydrogen-bonding, are capable of tuning the reduction potential of the cupredoxin azurin over a 700 mV range, surpassing the highest and lowest reduction potentials reported for any mononuclear cupredoxin, without perturbing the metal binding site beyond what is typical for the cupredoxin family of proteins. We also demonstrate that the effects of individual structural features are additive and that redox potential tuning of azurin is now predictable across the full range of cupredoxin potentials.

Electron flow through proteins

Electron transfers in photosynthesis and respiration commonly occur between metal-containing cofactors that are separated by large molecular distances. Employing laser flash-quench triggering methods, we have shown that 20-Å, coupling-limited Fe II–Ru III and Cu I–Ru III electron tunneling in Ru-modified cytochromes and blue copper proteins can occur on the microsecond timescale both in solutions and crystals. Redox equivalents can be transferred even longer distances by multistep tunneling, often called hopping, through intervening amino acid side chains. Our work has established that 20-Å hole hopping through an intervening tryptophan is two orders of magnitude faster than single-step electron tunneling in a Re-modified blue copper protein.

Transient EPR: using spin polarization in sequential radical pairs to study electron transfer in photosynthesis

The light induced electron transfer in photosynthesis generates a series of sequential spin polarized radical pairs, and transient electron paramagnetic resonance (TREPR) is ideally suited to study the lifetimes and physical and electronic structures of these radical pairs. In this article, the basic principles of TREPR are outlined with emphasis on the electron spin polarization (ESP) that develops during the electron transfer process. Examples of the analysis of TREPR data are given to illustrate the information that can be obtained. Recent applications of the technique to study the functionality of reaction centers, light-induced structural changes, and protein-cofactor interactions are reviewed.

Underdamped Vibrations Control the Primary Electron Transfer in Photosynthesis at Low Temperatures

Measurements performed with the help of ultrafast laser spectroscopy have clearly shown that the primary electron transfer in photosynthesis lasts no longer than a few picoseconds. Equally fast are processes of vibrational relaxation which have to be taken into account in the correct description of the phenomenon. Here, we consider a simple theory combining the electron transfer process with diffusion in the energy space of a chosen underdamped vibrational mode of protein environment. Analytical formulas for effective transition rate constants are derived, and a transient kinetics is considered. The quality of analytical approximations is verified by numerical simulations for various physical conditions. Efficient parallel computations have been applied. The model can explain a peculiar temperature dependence of pump-probe spectra observed.

Protein Dynamics Control the Kinetics of Initial Electron Transfer in Photosynthesis

The initial electron transfer dynamics during photosynthesis have been studied in Rhodobacter sphaeroides reaction centers from wild type and 14 mutants in which the driving force and the kinetics of charge separation vary over a broad range. Surprisingly, the protein relaxation kinetics, as measured by tryptophan absorbance changes, are invariant in these mutants. By applying a reaction-diffusion model, we can fit the complex electron transfer kinetics of each mutant quantitatively, varying only the driving force. These results indicate that initial photosynthetic charge separation is limited by protein dynamics rather than by a static electron transfer barrier.

Ultrafast Electron Transfer in Photosynthesis: Reduced Pheophytin and Quinone Interaction Mediated by Conical Intersections

The mechanism of electron transfer (ET) from reduced pheophytin (Pheo(-)) to the primary stable photosynthetic acceptor, a quinone (Q) molecule, is addressed by using high-level ab initio computations and realistic molecular models. The results reveal that the ET process involving the (Pheo(-) + Q) and (Pheo + Q(-)) oxidation states can be essentially seen as an ultrafast radiationless transition between the two hypersurfaces taking place via conical intersections (CIs). According to the present findings, an efficient ultrafast ET implies that the Pheo- and Q move toward each other in a given preferential parallel orientation, reaching the most effective arrangement for ET at intermolecular distances (R) around 5-3 Angstrom, where the lowest CIs are predicted. Favored donor/acceptor interactions are related to orientations with some overlap between the lowest occupied molecular orbitals (LUMO) of the two systems, and they lead to state-crossings at an earlier stage of the movement (larger R). Furthermore, when the topology of the interacting moieties does not make possible the LUMOs overlap, the corresponding diabatic potential energy curves do not intersect. Thus, it is anticipated that large scale motions, which are difficult to monitor experimentally, are actually occurring in the photosynthetic reaction centers of bacteria, algae, and higher plants, to fulfill the observed ultrafast ET processes.

Substitution of Isoleucine L177 by Histidine Affects the Pigment Composition and Properties of the Reaction Center of the Purple Bacterium Rhodobacter sphaeroides

Using site-directed mutagenesis, we obtained the mutant of the purple bacterium Rhodobacter sphaeroides with Ile to His substitution at position 177 in the L-subunit of the photosynthetic reaction center (RC). The mutant strain forms stable and photochemically active RC complexes. Relative to the wild type RCs, the spectral and photochemical properties of the mutant RC differ significantly in the absorption regions corresponding to the primary donor P and the monomer bacteriochlorophyll (BChl) absorption. It is shown that the RC I(L177)H contains only three BChl molecules compared to four BChl molecules in the wild type RC. Considering the fact that the properties of both isolated and membrane-associated mutant RCs are similar, we conclude that the loss of a BChl molecule from the mutant RC is caused by the introduced mutation but not by the protein purification procedure. The new mutant missing one BChl molecule but still able to perform light-induced reactions forming the charge-separated state P+QA- appears to be an interesting object to study the mechanisms of the first steps of the primary electron transfer in photosynthesis.

Dielectric and photoelectric properties of photosynthetic reaction centers

A brief review of studies of dielectric and photoelectric properties of photosynthetic reaction centers of purple bacteria as well as photosystem I and photosystem II of cyanobacteria and higher plants is given. A simple kinetic model of the primary processes of electron transfer in photosynthesis is used to discuss possible mechanisms of correlation between rate constant of charge transfer reaction, free energy of electron transition, and effective dielectric constant in the locus of corresponding carriers.