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In this paper, we discuss the explicit role of resonant nuclear/vibrational modes in mediating energy transport among chlorophylls in the Light-harvesting Complex II (LHCII), the major light-harvesting complex in green plants. The vibrational modes are considered to be resonant/quasi-resonant with the energy gap between electronic excitons. These resonant vibrations, along with the remaining nuclear degrees of freedom, constitute the environment/bath to the electronically excited system and contribute to two major phenomena: (a) decoherence and (b) incoherent phonon-mediated population relaxation. In this work, we explore the subtle interplay among the electronic excitation, the resonant vibrations, and the environment in dictating environment assisted quantum transport in light-harvesting complexes. We conclusively show that resonant vibrations are capable of boosting the incoherent population relaxation pathways and cause rapid decoherence. [ABSTRACT FROM AUTHOR]

1(a) and 1(b), respectively, it is clear that this feature emerges specifically as a result of HT activity[7] - remaining hidden by the inhomogenous broadening when the system is only vibronically mixed by FC activity through a Huang-Rhys factor similar to those found in LHCII.[9] In the model, this side-band can only be observed when additional vibronic mixing through HT activity is included. A growing body of work has pointed to vibronic mixing as a crucial design principle for efficient energy and charge transfer in natural[[1], [3]] and artificial systems.[[4]] Notable among these studies was the recent observation of vibronically promoted ultrafast energy flow in the major antenna complex of green plants and algae light-harvesting complex II (LHCII) - the most abundant membrane protein on the Earth[6] - via the emerging experimental technique two-dimensional electronic-vibrational (2DEV) spectroscopy.[3] This spectroscopy, which correlates electronic and nuclear degrees-of-freedom, shows promise for providing mechanistic insight into vibronic coupling; however, explicit theoretical input is necessary to extract such a detail. Electronic linear absorption spectra (top row) and 2DEV spectra (bottom row) for a heterodimer model without (a) and with (b) HT activity and (c) LHCII at 77 K. [Extracted from the article]

Fucoxanthin is an algae-specific xanthophyll of aquatic carotenoid. It is prevalent in brown seaweed because it functions as a light-harvesting complex for algal photosynthesis and photoprotection. Its exceptional chemical structure exhibits numerous biological activities that benefit human health. Due to these valuable properties, fucoxanthin's potential as a potent source for functional food, feed, and medicine is being explored extensively today. This article has thoroughly reviewed the availability and biosynthesis of fucoxanthin in the brown seaweed, as well as the mechanism behind it. We included the literature findings concerning the beneficial bioactivities of fucoxanthin such as antioxidant, anti-inflammatory, anti-obesity, antidiabetic, anticancer, and other potential activities. Last, an additional view on its potential as a functional food ingredient has been discussed to facilitate a broader application of fucoxanthin as a promising bioactive compound. [ABSTRACT FROM AUTHOR]

Photosynthesis involves light‐harvesting complexes where an array of antenna pigment channels the absorbed solar energy to the reaction centre of a photosystem. This work reports a supramolecular dendrimer‐dye assembly that mimics the natural light‐harvesting mechanism. A dendrimeric molecule based on two‐fluorophores has been constructed with three coumarin units at the end of three long arms and a 7‐diethylaminocoumarin unit at the interior. The molecule self‐aggregates in water into spherical micelles, which can encapsulate a rose‐bengal dye (RB). On excitation, peripheral coumarin units shuttled the energy to the loaded RB dye reaction center via a two‐step cascade resonance energy transfer (RET). The energy absorbed in the periphery is funnelled efficiently, resulting in a strong emission from the dye that resembles an energy funnel. The energy transfer cascade has been studied with both steady‐state and time‐resolved fluorescence spectroscopy. Molecular dynamics simulations of the self‐assembled aggregates in water were also in agreement with the experimental observations. [ABSTRACT FROM AUTHOR]

We simulate the long-range inter-complex electronic energy transfer in photosystem II--from the antenna complex, via a core complex, to the reaction center--using a non-Markovian (ZOFE) quantum master equation description that allows the electronic coherence involved in the energy transfer to be explicitly included at all length scales. This allows us to identify all locations where coherence is manifested and to further identify the pathways of the energy transfer in the full network of coupled chromophores using a description based on excitation probability currents. We investigate how the energy transfer depends on the initial excitation--localized, coherent initial excitation versus delocalized, incoherent initial excitation--and find that the overall energy transfer is remarkably robust with respect to such strong variations of the initial condition. To explore the importance of vibrationally enhanced transfer and to address the question of optimization in the system parameters, we systematically vary the strength of the coupling between the electronic and the vibrational degrees of freedom. We find that the natural parameters lie in a (broad) region that enables optimal transfer efficiency and that the overall long-range energy transfer on a ns time scale appears to be very robust with respect to variations in the vibronic coupling of up to an order of magnitude. Nevertheless, vibrationally enhanced transfer appears to be crucial to obtain a high transfer efficiency, with the latter falling sharply for couplings outside the optimal range. Comparison of our full quantum simulations to results obtained with a "classical" rate equation based on a modified-Redfield/generalized-Förster description previously used to simulate energy transfer dynamics in the entire photosystem II complex shows good agreement for the overall time scales of excitation energy transport. [ABSTRACT FROM AUTHOR]

We theoretically investigate a possibility that the symmetry of the repetitively branched structure of light-harvesting dendrimers creates the energy gradient descending toward inner generations (layers of pigment molecules) of the dendrimers. In the first half of this paper, we define a model system using the Frenkel exciton Hamiltonian that focuses only on the topology of dendrimers and numerically show that excitation energy tends to gather at inner generations of the model system at a thermal equilibrium state. This indicates that an energy gradient is formed in the model system. In the last half, we attribute this result to the symmetry of the model system and propose two symmetry-origin mechanisms creating the energy gradient. The present analysis and proposition are based on the theory of the linear chain (LC) decomposition [S. Koda, J. Chem. Phys. 142, 204112 (2015)], which equivalently transforms the model system into a set of one-dimensional systems on the basis of the symmetry of dendrimers. In the picture of the LC decomposition, we find that energy gradient is formed both in each linear chain and among linear chains, and these two mechanisms explain the numerical results well. [ABSTRACT FROM AUTHOR]

The excitation of molecular systems by natural incoherent light relevant, for example, to photosynthetic light-harvesting is examined. We show that the result of linear excitation with natural incoherent light can be obtained using incident light described in terms of transform limited pulses, as opposed to conventional classical representations with explicit random character. The derived expressions allow for computations to be done directly for any thermal light spectrum using a simple wave function formalism and provide a route to the experimental determination of natural incoherent excitation using pulsed laser techniques. Pulses associated with solar and cosmic microwave background radiation are provided as examples. [ABSTRACT FROM AUTHOR]

Silicon colloids are presented as efficient absorbers in the VIS-NIR region. The theory of resonant absorption by Mie modes in a single high-index sphere is reviewed and engineering rules established. The presented model predicts enhanced absorption in the crystalline silicon band-to-band absorption region, with absorption efficiencies exceeding one in the VIS and excellent NIR response. A maximum resonant absorption efficiency close to 4 can be obtained at the violet region (425 nm), and values above 0.25 are possible in the bandgap edge at wavelengths up to 1400 nm. Silicon colloids are proposed as a promising cost-effective, silicon saving, sunlight harvesters with improved VIS and NIR response. [ABSTRACT FROM AUTHOR]

Agronomic biofortification of crops with selenium (Se) is an important strategy to minimize hidden hunger and increase nutrient intake in poor populations. Selenium is an element that has several physiological and biochemical characteristics, such as the mitigation of different types of abiotic stress. Selenoproteins act as powerful antioxidants in plant metabolism through the glutathione peroxidase (GSH) pathway, and provide an increased activity for enzymatic (SOD, CAT, and APX) and non-enzymatic (ascorbic acid, flavonoids, and tocopherols) compounds that act in reactive oxygen species (ROS) scavenging system and cell detoxification. Selenium helps to inhibit the damage caused by climate changes such as drought, salinity, heavy metals, and extreme temperature. Also, Se regulates antenna complex of photosynthesis, protecting chlorophylls by raising photosynthetic pigments. However, Se concentrations in soils vary widely in the earth's crust. Soil Se availability regulates the uptake, transport, accumulation, and speciation in plants. Foliar Se application at the concentration 50 g ha−1 applied as sodium selenate increases the antioxidant, photosynthetic metabolism, and yield of several crops. Foliar Se application is a strategy to minimize soil adsorption and root accumulation. However, the limit between the beneficial and toxic effects of Se requires research to establish an optimal dose for each plant species under different edaphoclimatic conditions. In this review, we present the compilation of several studies on agronomic biofortification of plants with Se to ensure food production and food security to mitigate hidden hunger and improve the health of the population. • Se application at low concentration enhance chlorophyll and photosynthesis in plants. • Se activate the antioxidant metabolism in plants to combat ROS production. • Non-enzymatic compounds such ascorbic acid, flavonoids, and tocopherols are increased by Se application. • Se decrease damage caused by abiotic stresses such as drought, salinity, and extreme temperature. [ABSTRACT FROM AUTHOR]

The pathways and dynamics of excitation energy transfer between the chlorophyll (Chl) domains in solubilized trimeric and aggregated light-harvesting complex II (LHCII) are examined using two-dimensional electronic spectroscopy (2DES). The LHCII trimers and aggregates exhibit the unquenched and quenched excitonic states of Chl a, respectively. 2DES allows direct correlation of excitation and emission energies of coupled states over population time delays, hence enabling mapping of the energy flow between Chls. By the excitation of the entire Chl b Qy band, energy transfer from Chl b to Chl a states is monitored in the LHCII trimers and aggregates. Global analysis of the two-dimensional (2D) spectra reveals that energy transfer from Chl b to Chl a occurs on fast and slow time scales of 240-270 fs and 2.8 ps for both forms of LHCII. 2D decay-associated spectra resulting from the global analysis identify the correlation between Chl states involved in the energy transfer and decay at a given lifetime. The contribution of singlet-singlet annihilation on the kinetics of Chl energy transfer and decay is also modelled and discussed. The results show a marked change in the energy transfer kinetics in the time range of a few picoseconds. Owing to slow energy equilibration processes, long-lived intermediate Chl a states are present in solubilized trimers, while in aggregates, the population decay of these excited states is significantly accelerated, suggesting that, overall, the energy transfer within the LHCII complexes is faster in the aggregated state. [ABSTRACT FROM AUTHOR]

Although the study did not find kelp pigment impairment caused by exposure to coal constituents, kelp pigment analysis is still a useful means of assessing kelp health. Methods for assessing the potential for elevated concentrations of environmental chemicals that result in adverse health effects on aquatic macrophytes, including kelp, are limited. [Extracted from the article]

The light-harvesting chlorophyll a /b-binding (Lhc) superfamily, composed of several distinct antennae protein families, plays essential roles in light capture and photoprotection in plants. Compared with the extensive research in Arabidopsis thaliana and certain species, little is known about this superfamily in cassava (Manihot esculenta), an Euphorbiaceous plant experienced one so-called ρ recent whole-genome duplication (WGD). This study presents the first genome-wide identification of Lhc supergene family in cassava, resulting in 35 members that are distributed across 15 chromosomes. Phylogenetic analysis and BRH (Best Reciprocal Hit)-based sequence comparison assigned these genes into four previously defined families and 26 orthologous groups (including one absent from Arabidopsis). Synteny analysis showed that nine identified duplicates were derived from the WGD as well as local duplication, and retention bias of WGD duplicates in this species was shown to be something different from that in Arabidopsis which experienced two recent WGDs. Transcriptional profiling of MeLhc superfamily genes revealed a predominant expression pattern in green tissues such as leaf and midvein. Moreover, comparison of exon-intron structures, protein motifs, and gene expression profiles revealed divergence of duplicate pairs. Our findings will not only improve our knowledge on the evolution of this superfamily in cassava, but also provide valuable information for further functional studies. • This is the first genome-wide analysis of Lhc superfamily genes in cassava, an economically important Euphorbiaceous plant. • A high number of 35 members were found, which are unevenly distributed across 15 out of the 18 chromosomes. • Nine duplicates identified were shown to result from the so-called ρ recent WGD as well as local duplication. • Retention bias of WGD duplicates in cassava is different from Arabidopsis , a model plant experienced two recent WGDs. • Comparison of protein motifs and gene expression profiles revealed divergence of MeDof duplicates. [ABSTRACT FROM AUTHOR]

Biological systems are subjected to continuous environmental fluctuations, and therefore, flexibility in the structure and function of their protein building blocks is essential for survival. Protein dynamics are often local conformational changes, which allows multiple dynamical processes to occur simultaneously and rapidly in individual proteins. Experiments often average over these dynamics and their multiplicity, preventing identification of the molecular origin and impact on biological function. Green plants survive under high light by quenching excess energy, and Light-Harvesting Complex Stress Related 1 (LHCSR1) is the protein responsible for quenching in moss. Here, we expand an analysis of the correlation function of the fluorescence lifetime by improving the estimation of the lifetime states and by developing a multicomponent model correlation function, and we apply this analysis at the single-molecule level. Through these advances, we resolve previously hidden rapid dynamics, including multiple parallel processes. By applying this technique to LHCSR1, we identify and quantitate parallel dynamics on hundreds of microseconds and tens of milliseconds timescales, likely at two quenching sites within the protein. These sites are individually controlled in response to fluctuations in sunlight, which provides robust regulation of the light-harvesting machinery. Considering our results in combination with previous structural, spectroscopic, and computational data, we propose specific pigments that serve as the quenching sites. These findings, therefore, provide a mechanistic basis for quenching, illustrating the ability of this method to uncover protein function. [ABSTRACT FROM AUTHOR]

Abstract The light-harvesting 2 complex (LH2) of the purple phototrophic bacterium Rhodobacter sphaeroides is a highly efficient, light-harvesting antenna that allows growth under a wide-range of light intensities. In order to expand the spectral range of this antenna complex, we first used a series of competition assays to measure the capacity of the non-native pigments 3-acetyl chlorophyll (Chl) a , Chl d , Chl f or bacteriochlorophyll (BChl) b to replace native BChl a in the B800 binding site of LH2. We then adjusted the B800 site and systematically assessed the binding of non-native pigments. We find that Arg −10 of the LH2 β polypeptide plays a crucial role in binding specificity, by providing a hydrogen-bond to the 3-acetyl group of native and non-native pigments. Reconstituted LH2 complexes harbouring the series of (B)Chls were examined by transient absorption and steady-state fluorescence spectroscopies. Although slowed 10-fold to ~6 ps, energy transfer from Chl a to B850 BChl a remained highly efficient. We measured faster energy-transfer time constants for Chl d (3.5 ps) and Chl f (2.7 ps), which have red-shifted absorption maxima compared to Chl a. BChl b , red-shifted from the native BChl a , gave extremely rapid (≤0.1 ps) transfer. These results show that modified LH2 complexes, combined with engineered (B)Chl biosynthesis pathways in vivo , have potential for retaining high efficiency whilst acquiring increased spectral range. Highlights • The Rba. sphaeroides LH2 B800 site preferentially binds BChl a over other (B)Chls. • The BChl a 3-acetyl H-bond and B-ring structure contribute to B800 site specificity. • Removal of H-bonding by βArg −10 abolishes specificity for BChl a over Chl a. • Non-native (B)Chls in the B800 site rapidly and efficiently transfer energy to B850. • Engineering LH2 is a potential route to in vivo utilisation of non-native (B)Chls. [ABSTRACT FROM AUTHOR]

Light harvesting is a key step in photosynthesis but creation of synthetic light‐harvesting systems (LHSs) with high efficiencies has been challenging. When donor and acceptor dyes with aggregation‐induced emission were trapped within the interior of cross‐linked reverse vesicles, LHSs were obtained readily through spontaneous hydrophobically driven aggregation of the dyes in water. Aggregation in the confined nanospace was critical to the energy transfer and the light‐harvesting efficiency. The efficiency of the excitation energy transfer (EET) reached 95 % at a donor/acceptor ratio of 100:1 and the energy transfer was clearly visible even at a donor/acceptor ratio of 10 000:1. Multicolor emission was achieved simply by tuning the donor/acceptor feed ratio in the preparation and the quantum yield of white light emission from the system was 0.38, the highest reported for organic materials in water to date. [ABSTRACT FROM AUTHOR]

Highlights • Plants utilize super/megacomplexes to survive severe light conditions on land. • Several LHCII trimers can bind to the PSI–PSII megacomplex via the LHCI belt. • Excitation energy is diverted automatically to PSI in the megacomplex. • Megacomplexes help regulate the excitation energy in photosystems. Traditionally, two types of photosystem reaction centers (PSI and PSII) are thought to be spatially dispersed in the plant thylakoid membrane. In this model, PSI and PSII independently accept excitation energy from their own peripheral light-harvesting complexes, LHCI and LHCII, respectively, and form supercomplexes (PSI–LHCI and PSII–LHCII). However, recent studies using a combination of mild detergent treatment and spectroscopic analysis have revealed the existence of various megacomplexes such as a PSI–PSII megacomplex and a PSII megacomplex. Flexibility in the formation of supercomplexes and megacomplexes is important for land plants to regulate excitation energy to survive under strong and fluctuating sunlight on land. [ABSTRACT FROM AUTHOR]

Summary: In angiosperms, such as Arabidopsis and barley, the chloroplast NADH dehydrogenase‐like (NDH) complex associates with two copies of photosystem I (PSI) supercomplex to form an NDH−PSI supercomplex for the stabilization of the NDH complex. Two linker proteins, Lhca5 and Lhca6, are members of the light‐harvesting complex I (LHCI) family and mediate this supercomplex formation. The liverwort Marchantia polymorpha has branched from the basal land plant lineage and has neither Lhca5 nor Lhca6. Consequently, the NDH complex does not form a supercomplex with PSI in this plant. The Lhca6 gene does not seem to exist also in the moss Physcomitrella patens (Physcomitrella). Conversely, the Lhca5 gene has been found in Physcomitrella, although experimental evidence is still lacking for its contribution to NDH−PSI supercomplex formation as a linker. Here, we biochemically characterized the Lhca5 knock‐out mutant (lhca5) in Physcomitrella. The NDH−PSI supercomplex observed in wild‐type Physcomitrella was absent in the lhca5 mutant. Lhca5 protein was detected in this NDH−PSI supercomplex. Some PSI and NDH subunits were co‐immunoprecipitated with Lhca5−HA. These results indicate that the Physcomitrella gene is the functional ortholog of Lhca5 reported in Arabidopsis. Between Physcomitrella and Arabidopsis, the stromal loop region is highly conserved in Lhca5 proteins but not in other LHCI members. We found that Lhca5 contributed to the stable accumulation of the NDH complex, but part of the NDH complex was still sensitive to high light intensity, even in the wild‐type. We considered that angiosperms acquired another linker protein, Lhca6, to further stabilize the NDH complex. Significance Statement: In angiosperms, the chloroplast NDH complex is sandwiched between two copies of the PSI supercomplex via two linker proteins, Lhca5 and Lhca6. In the moss Physcomitrella patens, only the Lhca5 gene was conserved and contributes to NDH−PSI supercomplex formation. Lhca5‐dependent supercomplex formation is required for stabilization of the NDH complex, but the NDH complex is still sensitive to high light intensity, even in wild‐type Physcomitrella. During the evolution of land plants, another supercomplex formation via Lhca6 was necessary to further stabilize the NDH complex. [ABSTRACT FROM AUTHOR]

Abstract Although a multitude of theoretical studies exist on light-harvesting complex 2 (LH2), less is known about the light-harvesting complex 3 (LH3) of similar ring-like structure. In a comparative study of three system, i.e., the LH2 protein-pigment aggregate of the purple bacterium Rhodospirillum molischianum as well as for the LH2 and LH3 complexes of Rhodoblastus acidophilus the similarities and the differences in the excitonic system were analyzed. To this end, the systems have been studied in a multi-scale approach that combines molecular dynamics simulations with quantum chemistry calculations and quantum dynamics. Along the ground-state molecular dynamics trajectories, the excited energy gaps were determined in a quantum mechanics/molecular mechanics hybrid fashion. Based on the simulations, spectral densities, absorption spectra and exciton dynamics have been determined. After correcting for some shortcoming in the absorption spectra, the exciton dynamics within and between the ring systems have been determined and discussed. [ABSTRACT FROM AUTHOR]

Seven different carotenoids with the number of conjugated double bonds (N) from 5 to 11 were incorporated in vitro into carotenoidless complexes LH2 of the sulfur bacterium Allochromatium vinosum strain MSU. The efficiency of their incorporation varied from 4 to 99%. The influence of N in the carotenoid molecules on the energy transfer efficiency from these pigments to bacteriochlorophyll (BChl) in the modified LH2 complexes was studied for the first time. The highest level of energy transfer was recorded for rhodopin (N = 11) and neurosporene (N = 7) (37 and 51%, respectively). In the other carotenoids, this parameter ranged from 11 to 33%. In the LH2 complexes studied, we found no direct correlation between the decrease in N in carotenoids and increase in the energy transfer efficiency from these pigments to BChl. [ABSTRACT FROM AUTHOR]

Higher plant Photosystem I (PSI) includes a peripheral antenna system (LHCI) composed of four light-harvesting proteins (Lhca1-Lhca4). The LHCI system is highly conserved, suggesting that it plays a specific role within the LHC family. In order to elucidate the specific function of LHCI, the phenotype of an Arabidopsis mutant devoid of the whole LHCI system was studied over a range of conditions, including rapid changes in irradiation. ΔLhca plants displayed stunted growth and reduced thylakoid lumen acidification respect to wild type, suggesting that the lack of LHCI affected electron transport rate. Under rapidly changing light intensity, growth rate of the mutant was further reduced and the redox balance of the photosynthetic electron chain impaired. Instead, under constant, excess light regime, the ΔLhca plants did not suffer enhanced photooxidation vs. wild type, implying LHCI optimizes the flow rate through the electron transport chain by maintaining high PSI activity at all irradiances. We conclude that a complete PSI supercomplex, including LHCI, is crucial for the dynamic regulation of PQ redox state and therefore for PSII photoprotection. [ABSTRACT FROM AUTHOR]

Recently, we proposed a simple conceptual fluctuating antenna model (FAM), describing excitation diffusion and trapping in a continuous medium, where variations of the excitation transfer pathways are taken into account by the introduced fractional space dimension. Since then, this model has been successfully applied to simulate multi-exponential excitation quenching kinetics in a series of plant photosynthetic systems, purified from the thylakoid membranes, without invoking a radical pair state in the reaction centre. Here, we overview this model and its parameters obtained for various systems, and extend the area of its applications to several pigment-protein supercomplexes containing the photosystem I (PSI). We show that while the diffusion in the PSI core is virtually three-dimensional, the PSI core aggregates interconnected with other light-harvesting complexes (LHCI and/or LHCII) are characterized by a substantially reduced dimension, which indicates a smaller number of energy transfer links from LHCI to the PSI core. We also suggest that in vivo both PSI and PSII antennae are substantially larger than those observed in the isolated systems: PSII antenna contains in total about 6 LHCII trimers while PSI is aggregated with at least one LHCII trimer. The obtained results show that FAM can be a very useful tool to follow photosynthetic apparatus transformations during short- and long-term adaptation to varying light, monitored by kinetic fluorescence spectroscopy. [ABSTRACT FROM AUTHOR]

Photosynthetic organisms conserve the captured energy of solar radiation into stable chemical forms. To do so, they have evolved specialized systems of pigment-protein complexes consisting of light-harvesting antennas and reaction centres. Photosynthetic antennas contain remarkably dense arrangements of light-absorbing pigments held by the protein scaffold, and their function is to absorb light and funnel the excitation energy to the reaction centre. Decades of experimental and theoretical research resulted in a detailed understanding of the energy migration pathways within the photosynthetic apparatus. The key parameters determining the excitation relaxation and transfer are inter-pigment coupling and energetic disorder or non-equality of excitation energies at equivalent pigment sites due to the interaction with the disordered protein scaffold. Circularly symmetric light-harvesting antennas from purple bacteria present a beautiful example of the interplay between these parameters. The spectral signature of this interplay could be observed with the single-molecule fluorescence microscopy techniques. The results of these measurements were interpreted with an intuitively clear dichotomous model of disorder of pigment site energies. [ABSTRACT FROM AUTHOR]

Non-photochemical quenching (NPQ) is responsible for the protection of the photosynthetic apparatus of plants from photodamage at high-light conditions. It is commonly agreed that NPQ takes place in the major light-harvesting complexes (LHCII), however, its exact mechanisms are still under debate. Valuable information about its molecular nature can be provided by measuring time-resolved fluorescence (TRF) spectra of LHCII complexes and their aggregates. Previously [Chmeliov et al., Nat. Plants 2, 16045 (2016)], we analysed the corresponding TRF spectra using the multivariate curve resolution method and proposed a three-state model to describe the spectroscopic data. Usually, such data is described in terms of global analysis resulting in decay or evolution-associated spectra. In this work, we apply such analysis to the TRF data of LHCII aggregates and show that, although mathematically feasible, it cannot be directly related to the physical kinetic model. Nevertheless, a careful examination supplemented with additional spectroscopic information still results in the same three-state model proposed before. [ABSTRACT FROM AUTHOR]

The article reports on photoinhibition of photosynthesis is a well-known phenomenon in higher plants. It mentions that mosses from sunny habitats are considered photoinhibition tolerant because their photosynthetic apparatus has photoprotective mechanisms typical of vascular plants and green algae. It also mentions about the role of light-harvesting complex stress-related protein (LHCSR) proteins in thermal dissipation in photoinhibited mosses.

Natural light-harvesting is performed by pigment-protein complexes, which collect and funnel the solar energy at the start of photosynthesis. The identity and arrangement of pigments largely define the absorption spectrum of the antenna complex, which is further regulated by a palette of structural factors. Small alterations are induced by pigment-protein interactions. In light-harvesting systems 2 and 3 from Rhodoblastus acidophilus, the pigments are arranged identically, yet the former has an absorption peak at 850 nm that is blue-shifted to 820 nm in the latter. While the shift has previously been attributed to the removal of hydrogen bonds, which brings changes in the acetyl moiety of the bacteriochlorophyll, recent work has shown that other mechanisms are also present. Using computational and modeling tools on the corresponding crystal structures, we reach a different conclusion: The most critical factor for the shift is the curvature of the macrocycle ring. The bending of the planar part of the pigment is identified as the second-most important design principle for the function of pigment-protein complexes--a finding that can inspire the design of novel artificial systems. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the key coloured compounds (anthocyanins, carotenoids…etc) and the key proteins associated to their synthesis or degradation of peach fruit peel ( Prunus persica ‘Hujingmilu’) using iTRAQ techniques at different peach developmental stages and during the postharvest period. Peach fruits were collected 50 d, 90 d, 95 d, 100 d, and 105 day after flowering, as well as fruits being stored for 3 days after picking at 105 days after flowering. The key coloured compounds of ‘Hujingmilu ‘honey peach peel is composed of, among others, chlorophyll, anthocyanin, carotenoids, zeaxanthin, and lycopene. Peel color was regulated by chlorophyll degradation pathways, carotenoid metabolism pathways, and anthocyanin metabolism pathways, the iTRAQ technique identified 1848 unique proteins, of which 842 were related to biological processes, and 25 were related to color and 33 were related to energy transfer during fruit development and postharvest. During the development of peach fruit, light-harvesting complex chlorophyll a/b binding protein (CAB) and protochlorophyllide reductase(POR) are the key functional proteins for regulating chlorophyll metabolism, anthocyanidin 3-O-glucosyltransferase (3 G T) and UFGT are the key functional proteins for regulating anthocyanidin metabolism, PSY, zeta-carotene desaturase (ZCD) and carotenoid cleavage dioxygenase (CCD) are the key functional proteins for regulating carotenoid metabolism during the development and the postharvest period of peach fruit. Mg-protoporphyrin IX chelatase and pheophorbide a oxygenase (PAO) are the key functional proteins for regulating chlorophyll metabolism during postharvest. The key proteins were regulated a little earlier or accompany with the increase or decrease of peach peel coloured compounds. These results provide further understanding of the key coloured compounds of peach peel color, key proteins associated to coloured compounds, and reveal how the differential proteins take part in coloured compound metabolism pathway during fruit development and postharvest. [ABSTRACT FROM AUTHOR]

Owing to their versatile optical and electrical properties, semiconductor quantum dots are attracting attention as a material of choice for solar energy conversion. The quantum dot sensitized solar cells are considered as one of the most promising nextgeneration solar cells as they have the advantage of tunable band-gap energy and multiple exciton generation. We present here a study on quantum dot sensitized solar cells considering their construction and working, impact of incorporation of nanomaterials in solar cells and various structures for improving the performance of solar cells. [ABSTRACT FROM AUTHOR]

Oxygenic photosynthesis is conducted by two photoactive units, photosystem I (PSI) and photosystem II (PSII), that utilize light energy to generate the electron flow from water to NADPH. Photosynthetic organisms have developed a mechanism called state transition (ST) to regulate the excitation balance between the two units, since the balance is constantly disturbed by fluctuation in light quality. The traditional ST model assumes shuttling of a light-harvesting complex called LHCII between the two PSs. However, there has been no direct observation of the intracellular rearrangements of LHCII upon ST, which is crucial in order to evaluate the validity of the traditional ST model. Here, the intracellular distributions of the two PSs and LHCII are visualized by using a novel cryogenic optical microscope. The calculated Pearson's correlation coefficient between the relative fluorescence intensity of LHCII and the fluorescence intensity ratio of PSII to PSI provided information about the degree of co-localization of these components. The analysis indicated that the relative emission intensity from LHCII is stronger in the PSII-abundant region than in the PSI-abundant one in both states. On the other hand, a statistical analysis by Welch's test indicated that Pearson's correlation coefficient is significantly higher in state1 than state2, probably reflecting the movement of LHCII from PSII to PSI upon state transition. The study also found an independent cell group in which degree of ST was between those observed for fully converted cells. These cells tended to show lower correlation coefficients than the fully converted ones. This was explained by assuming the existence of free LHCII, which moves to but remains unconnected to PSI in state2. [ABSTRACT FROM AUTHOR]

Phycoerythrobilin (PEB) is an open-chain tetrapyrrole derived from heme and plays an important role as light-harvesting pigment in the phycobiliproteins of cyanobacteria and red algae. Furthermore, PEB can also function as an antioxidant with potential use as a natural acid stable food colorant. PEB is not commercially available and large, pure quantities can only be obtained by laborious methanolysis of red algae followed by liquid chromatography. Here we describe an improved method for high yield production and purification of PEB in Escherichia coli via heterologous expression where the two required enzymes heme oxygenase and PEB synthase subsequently convert the substrate heme provided by the host cell. Experiments in shaking flasks resulted in the highest product yield of 680.23 ± 42.75 μg PEB per g cell dry weight, by induction with 0.1 mM IPTG. Scale-up to batch-operated fermentation in a 2 L bioreactor reached product concentrations up to 5.02 mg PEB L −1 by adjustment of aeration, induction time, media composition and supplementation of precursors. A further approach included separation of PEB from developed foam above the culture. This enabled continuous product collection during cultivation and simplified product purification. Produced PEB was validated via UV–vis spectroscopy, high pressure liquid chromatography and mass spectrometry. [ABSTRACT FROM AUTHOR]

Fucoxanthin chlorophyll (Chl) a / c protein (FCP) is the major light-harvesting complex found in aquatic photosynthetic organisms such as diatoms and brown algae. In FCP, fucoxanthin and Chl- c absorb light in the blue-green region, and both of the antenna pigments transfer the excitation energy to Chl- a . Chl- c is characterized by the 17-acrylate moiety (17-CH CH COOH) conjugated to the porphyrin backbone, extending its π-conjugation. Protonation (17-CH CH COOH) or deprotonation (17-CH CH COO − ) of the acrylate moiety is capable of affecting the optical properties of Chl- c . In this study, we purified the FCP from Chaetoceros calcitrans , a diatom, and measured its electronic absorption, circular dichroism, fluorescence, and fluorescence-excitation spectra in buffer solutions at different pH values. A pH-dependent change was clearly observed at the Soret absorption band of Chl- c . Based on the change, the acid-dissociation constant of Chl- c , pKa, was determined to be 5.3 ± 0.2. Moreover, fluorescence spectroscopy revealed that a decrease in the energy transfer efficiency from Chl- c to Chl- a under acidic condition. The present results demonstrate that acid-dissociation of Chl- c occurs even while bound to FCP, thus giving a new insight into the photosynthetic function of Chl- c bound to the pigment-protein complexes. [ABSTRACT FROM AUTHOR]

The article explores the structure of plant photosystem I (PSI) and its complexes which form a supercomplex with light-harvesting complex (LHC). The PSI reaction center complex functions with the electron transport chain (ETC) harbored by the principal subunits PsaA and PsaB. The light-harvesting complex is considered the most prominent addition to the PSI structure with all structures containing three carotene molecules.

Light-harvesting complexes (LHCs) serve a dual role in photosynthesis, depending on the prevailing light conditions. In low light, they ensure photosynthetic efficiency by maximizing the light absorption cross-section and subsequent energy storage. Under excess light conditions, LHCs perform photoprotective quenching functions to prevent harmful chemical species such as triplet chlorophyll and singlet oxygen from forming and damaging the photosynthetic apparatus. In this Minireview, various photoprotective quenching mechanisms that have been identified in different photosynthetic organisms are surveyed and summarized, and implications for improving photosynthetic productivity are briefly discussed. [ABSTRACT FROM AUTHOR]

Photosynthetic organisms are frequently exposed to light intensities that surpass the photosynthetic electron transport capacity. Under these conditions, the excess absorbed energy can be transferred from excited chlorophyll in the triplet state (3Chl*) to molecular O2, which leads to the production of harmful reactive oxygen species. To avoid this photooxidative stress, photosynthetic organisms must respond to excess light. In the green alga Chlamydomonas reinhardtii, the fastest response to high light is nonphotochemical quenching, a process that allows safe dissipation of the excess energy as heat. The two proteins, UV-inducible LHCSR1 and blue light-inducible LHCSR3, appear to be responsible for this function. While the LHCSR3 protein has been intensively studied, the role of LHCSR1 has been only partially elucidated. To investigate the molecular functions of LHCSR1 in C. reinhardtii, we performed biochemical and spectroscopic experiments and found that the protein mediates excitation energy transfer from lightharvesting complexes for Photosystem II (LHCII) to Photosystem I (PSI), rather than Photosystem II, at a low pH. This altered excitation transfer allows remarkable fluorescence quenching under high light. Our findings suggest that there is a PSI-dependent photoprotection mechanism that is facilitated by LHCSR1. [ABSTRACT FROM AUTHOR]

Real-time visualization of assembly processes and sophisticated signal processing at the nanoscale are two challenging topics in photonic nanomaterials. Here, high-quality light-harvesting crystalline nanorods were developed by the coassembly of two polypyridyl Ir(III) and Ru(II) metallophosphors, behaving as the antenna chromophore and energy acceptor, respectively. By using a one-pot or stepwise growth condition, homogeneous and multiblock heterojunction nanorods were prepared, respectively. These nanostructures display multicolor phosphorescence from green to red due to the efficient triplet energy transfer and light-harvesting capability at low acceptor doping ratios. Heterojunction nanorods show gradient emission-color switches during different growth stages, in which the real-time stepwise assembly can be vividly visualized using fluorescence microscopy techniques. Triplet excitons were successfully manipulated in both homogeneous and heterojunction nanorods to realize waveguided green, orange, and red emissions and advanced photonic signal logics and encoding/decoding on single multiblock heterojunction nanorod. [ABSTRACT FROM AUTHOR]

In this work, we report a simple strategy by mixing a naphthyl-substituted 9,10-bis((E)-2-(pyridin-4-yl)vinyl)anthracene (BP4VA) and cucurbit[8]uril (CB[8]) in aqueous solution, based on the host-guest complexation between CB[8] and a BP4VA derivative ( 1 ), to construct supramolecular polymers. The host-guest interaction between CB[8] and naphthyl efficiently restricted the intramolecular rotation and the non-radiative relaxation channel, thereby resulting in the strong emission in dilute solution. We further investigate the self-assembly behaviors of the complex between CB[8] and 1 . The aggregated species of the supramolecular polymers in aqueous solution exhibited nanorods structures with a relatively wide size distribution ranging from 60 to 200 nm, which showed potential application as highly efficient aqueous light-harvesting systems by using supramolecular polymers as energy donor and sulfo-cyanine5 carboxylic acid (Cy5) as energy acceptor. [ABSTRACT FROM AUTHOR]

The first step in chlorophyll a degradation is the extraction of the central Mg. This reaction is catalyzed by Mg-dechelatase encoded by Stay-Green ( SGR ) in land plants. SGR extracts Mg from chlorophyll a but not from chlorophyll b , and chlorophyll b must be converted to chlorophyll a before degradation. The first reaction of the chlorophyll b to chlorophyll a conversion is catalyzed by chlorophyll b reductase. Non-Yellow Coloring 1 (NYC1) and NYC1 like (NOL) are isozymes of chlorophyll b reductase. When SGR was transiently overexpressed in Arabidopsis , both chlorophyll a and b were degraded, suggesting that the chlorophyll b to chlorophyll a conversion is activated by SGR overexpression. To examine the involvement of chlorophyll b reductases in SGR-induced chlorophyll b degradation, SGR was transiently overexpressed in nyc1 , nol , and nyc1 nol double mutants by dexamethasone treatment. It was found that in the wild type and nol mutant, chlorophyll a and b were degraded and all the chlorophyll-binding proteins decreased. Meanwhile, in nyc1 and nyc1 nol mutants, chlorophyll b degradation was suppressed and the light-harvesting complex of photosystem II remained. The mRNA and protein levels of NYC1 increased after SGR overexpression in wild type plants. These results suggest that Mg-dechelation of chlorophyll a by SGR activates chlorophyll b degradation by inducing the expression of NYC1 . This is an effective regulation of a metabolic pathway. [ABSTRACT FROM AUTHOR]

The LH2 protein has two types of bacteriochlorophyll (BChl) a termed B800 and B850 BChl a . Substitution of B800 BChl a with chlorophyll (Chl) a derivatives in this protein has considerable attention from the viewpoints of elucidation of the energy transfer mechanism and developments of artificial photosynthetic devices based on the LH2 structure. Herein we examine reconstitution properties of Chl a and 13 2 -demethoxycarbonyl Chl a (pyroChl a ) into the B800 binding sites in LH2 from the purple photosynthetic bacterium Rhodoblastus ( Rbl .) acidophilus . Both the Chl a derivatives were successfully inserted into the B800 binding sites in the LH2 protein whose B800 BChl a was removed (B800-free LH2), and the energy transfer from these derivatives to B850 BChl a was observed in the reconstituted LH2 proteins. Extraction of chlorophyllous pigments from the reconstituted LH2 proteins allows us to estimate the occupancy of Chl a and pyroChl a in the nine B800 binding sites from the molar ratio of (pyro)Chl a to residual B850 BChl a : the occupancy of Chl a was 72% and was 1.2-times larger than that of pyroChl a . These results indicate that Chl a and pyroChl a can be accommodated in the B800 binding sites in the LH2 protein derived from this bacterium, but the affinity of pyroChl a would be slightly smaller than that of Chl a . The binding properties of Chl a derivatives into the B800 binding sites in LH2 will be useful for manipulation of light-harvesting abilities in photosynthetic antenna proteins. [ABSTRACT FROM AUTHOR]

The photosystem II (PSII) supercomplex splits water utilizing light energy and is composed of a core dimer complex surrounded by light-harvesting complexes (LHCs). In green algae, the major LHCs which are LHCII trimers have thus far been categorized into strongly, moderately, or loosely binding LHCII trimers based on their predicted binding to core complexes. However, the binding energies have been indirectly predicted based on the presence or absence of LHCII trimers in the PSII supercomplex under electron microscopy and have not been determined experimentally. In this study, we investigated the binding of LHCII trimers by analyzing thermodynamic dissociation kinetics using isolated PSII supercomplexes. We identified two activation energies for dissociation of LHCII trimers: 54 ± 19 and 134 ± 8 kJ/mol. This result indicated the types of intermolecular interactions between LHCII trimers and core complexes. [ABSTRACT FROM AUTHOR]

The photosynthetic complex CP26, one of the minor antennae of the photosystem II, plays an important role in regulation of the excitation energy transfer in the PSII. Due to instability during isolation and purification, it remained poorly studied from the viewpoint of theoretical chemistry because of the absence of X-ray crystallography data. In this work, using the recently determined three-dimensional structure of the complex we apply the quantum chemical approach to study the properties of exciton states in it. Spectral properties, structure of exciton states and roles of the pigments in the complex and photosystem II are discussed. [ABSTRACT FROM AUTHOR]

Strong excitonic interactions are a key design strategy in photosynthetic light harvesting, expanding the spectral cross-section for light absorption and creating considerably faster and more robust excitation energy transfer. These molecular excitons are a direct result of exceptionally densely packed pigments in photosynthetic proteins. The main light-harvesting complexes of diatoms, known as fucoxanthin-chlorophyll proteins (FCPs), are an exception, displaying surprisingly weak excitonic coupling between their chlorophyll (Chl) a's, despite a high pigment density. Here,we show, using single-molecule spectroscopy, that the FCP complexes of Cyclotella meneghiniana switch frequently into stable, strongly emissive states shifted 4-10 nm toward the red. A few percent of isolated FCPa complexes and -20% of isolated FCPb complexes, on average, were observed to populate these previously unobserved states, percentages that agree with the steady-state fluorescence spectra of FCP ensembles. Thus, the complexes use their enhanced sensitivity to static disorder to increase their light-harvesting capability in a number of ways. A disordered exciton model based on the structure of the main plant light-harvesting complex explains the red-shifted emission by strong localization of the excitation energy on a single Chl a pigment in the terminal emitter domain due to very specific pigment orientations. We suggest that the specific construction of FCP gives the complex a unique strategy to ensure that its light-harvesting function remains robust in the fluctuating protein environment despite limited excitonic interactions. [ABSTRACT FROM AUTHOR]

The majority of life on Earth depends directly or indirectly on the sun as a source of energy. The initial step of photosynthesis is facilitated by light-harvesting complexes, which capture and transfer light energy into the reaction centers (RCs). Here, we analyzed the organization of photosynthetic (PS) complexes in the bacterium G. phototrophica, which so far is the only phototrophic representative of the bacterial phylum Gemmatimonadetes. The isolated complex has a molecular weight of about 800 ± 100 kDa, which is approximately 2 times larger than the core complex of Rhodospirillum rubrum. The complex contains 62.4 ± 4.7 bacteriochlorophyll (BChl) a molecules absorbing in 2 distinct infrared absorption bands with maxima at 816 and 868 nm. Using femtosecond transient absorption spectroscopy, we determined the energy transfer time between these spectral bands as 2 ps. Single particle analyses of the purified complexes showed that they were circular structures with an outer diameter of approximately 18 nm and a thickness of 7 nm. Based on the obtained, we propose that the LH complexes in G. phototrophica form 2 concentric rings surrounding the type 2 RC. The inner ring (corresponding to the B868 absorption band) is composed of 15 subunits and is analogous to the inner light-harvesting complex 1 (LH1) in purple bacteria. The outer ring is composed of 15 more distant BChl dimers with no or slow energy transfer between them, resulting in the B816 absorption band. This completely unique and elegant organization offers good structural stability, as well as high efficiency of light harvesting. Our results reveal that while the PS apparatus of Gemmatimonadetes was acquired via horizontal gene transfer from purple bacteria, it later evolved along its own pathway, devising a new arrangement of its light harvesting complexes. [ABSTRACT FROM AUTHOR]

Three sets of tetrapyrrole-chromophore arrays have been examined that exhibit panchromatic absorption across large portions of the near-ultraviolet (NUV) to nearinfrared (NIR) spectrum along with favorable excited-state properties for use in solar-energy conversion. The arrays vary the tetrapyrrole (porphyrin, chlorin, bacteriochlorin), chromophore (boron-dipyrrin, perylene, terrylene), and attachment sites (meso-position, β-pyrrole position). In all, seven dyads, one triad, and nine benchmarks in toluene and benzonitrile were studied using steady-state and time-resolved absorption and fluorescence spectroscopy. The results were analyzed with the aid of density functional theory (DFT) and time-dependent DFT calculations. Natural transition orbitals (NTOs) were constructed to assess the net change in electron density associated with each NUV-NIR absorption transition. The porphyrin- perylene dyad P-PMI displays the most even spectral coverage from 400 to 700 nm, with an average ε ∼ 43 000 M-1 cm-1. A significant contributor is a chromophore-induced reduction in the configuration interaction involving the four frontier molecular orbitals of benchmark porphyrins and associated constructive/destructive transition-dipole interference that results in intense (ε ∼ 400 000 M-1 cm-1) NUV and weak (<20 000 M-1 cm-1) visible features. P-PMI has an S1 lifetime (τs) of 4.7 ns in toluene and 1.3 ns in benzonitrile. Bacteriochlorin analogue BC-PMI has more extended spectral coverage (350-750 nm) and τs = 2.8 ns in toluene and 30 ps in benzonitrile. Terrylene analogue P-TMI has intermediate optical characteristics with τs = 310 ps in toluene and 150 ps in benzonitrile. The NTOs for most arrays show that S0 → S1 primarily involves the tetrapyrrole, but for PTMI the NTOs have electron density delocalized over the two units as a result of extensive orbital mixing. Collectively, the insights obtained should aid the design of tetrapyrrole-based architectures for panchromatic light-harvesting systems for solarenergy conversion. [ABSTRACT FROM AUTHOR]

It is demonstrated an effective to significantly improve the photocatalytic acitivity of BiOCl hierichial nanosheets by creating oxygen vacancies. These oxygen-deficient BiOCl nanosheets prepared via a two-step process exhibit substantially enhanced photocatalytic performance toward dye degradation when compared to the pristine BiOCl nanosheets. Such the superior photocatalytic performance is owing to the improved light-harvesting ability and increased doner density as a result of the induced oxygen vacancies. [ABSTRACT FROM AUTHOR]

The reaction centre-light harvesting 1 (RC-LH1) complex of Thermochromatium ( Tch. ) tepidum has a unique calcium-ion binding site that enhances thermal stability and red-shifts the absorption of LH1 from 880 nm to 915 nm in the presence of calcium-ions. The LH1 antenna of mesophilic species of phototrophic bacteria such as Rhodobacter ( Rba. ) sphaeroides does not possess such properties. We have engineered calcium-ion binding into the LH1 antenna of Rba. sphaeroides by progressively modifying the native LH1 polypeptides with sequences from Tch. tepidum . We show that acquisition of the C-terminal domains from LH1 α and β of Tch. tepidum is sufficient to activate calcium-ion binding and the extent of red-shifting increases with the proportion of Tch. tepidum sequence incorporated. However, full exchange of the LH1 polypeptides with those of Tch. tepidum results in misassembled core complexes. Isolated α and β polypeptides from our most successful mutant were reconstituted in vitro with BChl a to form an LH1-type complex, which was stabilised 3-fold by calcium-ions. Additionally, carotenoid specificity was changed from spheroidene found in Rba. sphaeroides to spirilloxanthin found in Tch. tepidum , with the latter enhancing in vitro formation of LH1. These data show that the C-terminal LH1 α/β domains of Tch. tepidum behave autonomously, and are able to transmit calcium-ion induced conformational changes to BChls bound to the rest of a foreign antenna complex. Thus, elements of foreign antenna complexes, such as calcium-ion binding and blue/red switching of absorption, can be ported into Rhodobacter sphaeroides using careful design processes. [ABSTRACT FROM AUTHOR]

Light-harvesting-like (LIL) proteins are a group of proteins that share a consensus amino acid sequence with light-harvesting Chl-binding (LHC) proteins. We hypothesized that they might be involved in photosynthesis-related processes. In order to gain a better understanding of a potential role in photosynthesis-related processes, we examined the most recently identified LIL protein, LIL8/PSB33. Recently, it was suggested that this protein is an auxiliary PSII core protein which is involved in organization of the PSII supercomplex. However, we found that the majority of LIL8/PSB33 was localized in stroma lamellae, where PSI is predominant. Moreover, the PSI antenna sizes measured under visible light were slightly increased in the lil8 mutants which lack LIL8/PSB33 protein. Analysis of fluorescence decay kinetics and fluorescence decay-associated spectra indicated that energy transfer to quenching sites within PSI was partially hampered in these mutants. On the other hand, analysis of the steady-state fluorescence spectra in these mutants indicates that a population of LHCII is energetically disconnected from PSII. Taken together, we suggest that LIL8/PSB33 is involved in the fine-tuning of light harvesting and/or energy transfer around both photosystems. [ABSTRACT FROM AUTHOR]