Efficient Photosynthetic Systems Research Articles

The potential of microalgae for carbon capture and sequestration

Microalgae have been highlighted as a contributor to CO2 sequestration due to their efficient photosynthetic system. However, calculations on their actual potential for CO2 sequestration are often lacking. Here, we calculated the potential of microalgae for the capture of CO2 by integrating it with a large emitter (gas-based energy plant) and a low emitter (dairy farms), and also discussed if such integrated systems can be considered as carbon sequesters given that the final use of the biomass often quickly releases the captured CO2. Moreover, the CO2 footprint of microalgal systems is highlighted as a critical point of attention for future developments. Such considerations are of utmost importance to avoid false promises that ultimately harm this sector, as large investments are made following untruthful claims that, when proven wrong, result in a loss of interest. Finally, key definitions are proposed to improve clarity and help in such discussions.

Improvement in the photoprotective capability benefits the productivity of a yellow-green wheat mutant in N-deficient conditions

Wheat yellow-green mutant Jimai5265yg has a more efficient photosynthetic system and higher productivity than its wild type under N-deficient conditions. To understand the relationship between photosynthetic properties and the grain yield, we conducted a field experiment under different N application levels. Compared to wild type, the Jimai5265yg flag leaves had higher mesophyll conductance, photosynthetic N-use efficiency, and photorespiration in the field without N application. Chlorophyll a fluorescence analysis showed that PSII was more sensitive to photoinhibition due to lower nonphotochemical quenching (NPQ) and higher nonregulated heat dissipation. In N-deficient condition, the PSI acceptor side of Jimai5265yg was less reduced. We proposed that the photoinhibited PSII protected PSI from over-reduction through downregulation of electron transport. PCA analysis also indicated that PSI photoprotection and electron transport regulation were closely associated with grain yield. Our results suggested that the photoprotection mechanism of PSI independent of NPQ was critical for crop productivity.

Robust Heterogeneous Photocatalyst for Visible-Light-Driven Hydrogen Evolution Promotion: Immobilization of a Fluorescein Dye-Encapsulated Metal-Organic Cage on TiO2.

The design of artificial photocatalytic devices that simulates the ingenious and efficient photosynthetic systems in nature is promising. Herein, a metal-organic cage [Pd6(NPyCzPF)12]12+ (MOC-PC6) integrating 12 organic ligands NPyCzBP and 6 Pd2+ catalytic centers is designed, which is well defined to include organic dye fluorescein (FL) for constructing a supramolecular photochemical molecular device (SPMD) FL@MOC-PC6. Photoinduced electron transfer (PET) between MOC-PC6 and the encapsulated FL has been observed by steady-state and time-resolved emission spectroscopy. FL@MOC-PC6 is successfully heterogenized with TiO2 by a facile sol-gel method to achieve a robust heterogeneous FL@MOC-PC6-TiO2. The close proximity between the Pd2+ catalytic site and FL included in the cage enables PET from the photoexcited FL to Pd2+ sites through a powerful intramolecular pathway. The photocatalytic hydrogen production assessments of the optimized 4 wt % FL@MOC-PC6-TiO2 demonstrate an initial H2 production rate of 2402 μmol g-1 h-1 and a turnover number of 4356 within 40 h, enhanced by 15-fold over that of a homogeneous FL@MOC-PC6. The effect of the MOC content on photocatalytic H2 evolution (PHE) is investigated and the inefficient comparison systems, such as MOC-PC6, MOC-PC6-TiO2, FL-sensitized MOC-PC6/FL-TiO2, and analogue FL/MOC-PC6-TiO2 with free FL, are evaluated. This study provides a creative and distinctive approach for the design and preparation of novel heterogeneous SPMD catalysts based on MOCs.

Roles of Si and SiNPs in Improving Thermotolerance of Wheat Photosynthetic Machinery via Upregulation of PsbH, PsbB and PsbD Genes Encoding PSII Core Proteins

Photosystem II is extremely susceptible to environmental alterations, particularly high temperatures. The maintenance of an efficient photosynthetic system under stress conditions is one of the main issues for plants to attain their required energy. Nowadays, searching for stress alleviators is the main goal for maintaining photosynthetic system productivity and, thereby, crop yield under global climate change. Potassium silicate (K2SiO3, 1.5 mM) and silicon dioxide nanoparticles (SiO2NPs, 1.66 mM) were used to mitigate the negative impacts of heat stress (45 °C, 5 h) on wheat (Triticum aestivum L.) cv. (Shandawelly) seedlings. The results showed that K2SiO3 and SiO2NPs diminished leaf rolling symptoms and electrolyte leakage (EL) of heat-stressed wheat leaves. Furthermore, the maximum quantum yield of photosystem II (Fv/Fm) and the performance index (PIabs), as well as the photosynthetic pigments and organic solutes including soluble sugars, sucrose, and proline accumulation, were increased in K2SiO3 and SiO2NPs stressed leaves. At the molecular level, RT-PCR analysis showed that K2SiO3 and SiO2NPs treatments stimulated the overexpression of PsbH, PsbB, and PsbD genes. Notably, this investigation indicated that K2SiO3 was more effective in improving wheat thermotolerance compared to SiO2NPs. The application of K2SiO3 and SiO2NPs may be one of the proposed approaches to improve crop growth and productivity to tolerate climatic change.

Structural variability, coordination and adaptation of a native photosynthetic machinery.

Cyanobacterial thylakoid membranes represent the active sites for both photosynthetic and respiratory electron transport. We used high-resolution atomic force microscopy to visualize the native organization and interactions of photosynthetic complexes within the thylakoid membranes from the model cyanobacterium Synechococcus elongatus PCC 7942. The thylakoid membranes are heterogeneous and assemble photosynthetic complexes into functional domains to enhance their coordination and regulation. Under high light, the chlorophyll-binding proteins IsiA are strongly expressed and associate with Photosystem I (PSI), forming highly variable IsiA-PSI supercomplexes to increase the absorption cross-section of PSI. There are also tight interactions of PSI with Photosystem II (PSII), cytochrome b6f, ATP synthase and NAD(P)H dehydrogenase complexes. The organizational variability of these photosynthetic supercomplexes permits efficient linear and cyclic electron transport as well as bioenergetic regulation. Understanding the organizational landscape and environmental adaptation of cyanobacterial thylakoid membranes may help inform strategies for engineering efficient photosynthetic systems and photo-biofactories.

A wish list for synthetic biology in photosynthesis research.

This perspective summarizes the presentations and discussions at the ' International Symposium on Synthetic Biology in Photosynthesis Research', which was held in Shanghai in 2018. Leveraging the current advanced understanding of photosynthetic systems, the symposium brain-stormed about the redesign and engineering of photosynthetic systems for translational goals and evaluated available new technologies/tools for synthetic biology as well as technological obstacles and new tools that would be needed to overcome them. Four major research areas for redesigning photosynthesis were identified: (i) mining natural variations of photosynthesis; (ii) coordinating photosynthesis with pathways utilizing photosynthate; (iii) reconstruction of highly efficient photosynthetic systems in non-host species; and (iv) development of new photosynthetic systems that do not exist in nature. To expedite photosynthesis synthetic biology research, an array of new technologies and community resources need to be developed, which include expanded modelling capacities, molecular engineering toolboxes, model species, and phenotyping tools.

Photochemical Properties of Host-Guest Supramolecular Systems with Structurally Confined Metal-Organic Capsules.

Inspired by natural photosynthesis, researchers have designed symmetric metal-organic hosts with large inner pockets that are spontaneously generated through preorganized ligands and functionalized metallocorners to construct dye-containing host-guest systems. The abundant noncovalent interaction sites in the pockets of the hosts facilitated substrate-catalyst interactions for possible enrichment, fixation, and activation of substrates/reagents, providing special electron transfer pathways for regio- or stereoselectively photocatalytic chemical transformations. In this Account, we focus our attention on metal-organic hosts that contain photoactive or redox-active units to evaluate electron transfer and charge separation between host and guest units in these supramolecular systems and elucidate the related photoinduced chemical reactions controlled by these electron transfer processes within the structurally confined pockets of these interesting metal-organic hosts. We have been engaged in developing methods to isolate a series of chromophores for charge separation in supramolecular systems, incorporating organic dyes as photosensitizers in metal-organic hosts with electron acceptor/donor guests is a promising way to enable typical enzyme-like photocatalytic transformations within a confined microenvironment. Related to these inter- and intramolecular photoinduced electron transfer (PET) processes, the formation of host-guest supramolecular systems to fix and isolate the donor-acceptor pair with a short through-space distance provided a new PET pathway to stabilize the charge-separated ion pair. Highly efficient photosynthetic systems can be obtained when charge transfer to electron donors/acceptors occurs faster than the charge recombination. This Account starts with a brief summary of the potential approaches for constructing photoactive metal-organic hosts through the incorporation of dye molecules within ligand backbones or as a part of the metal nodes of the architecture. Following the methodological summary is a discussion on the mechanisms governing the photoinduced charge separation and electron transfer pathways within the dye-incorporated metal-organic hosts. We also searched for strategies for constructing photoactive supramolecular systems through encapsulating dye molecules within the inner space of redox-active hosts. The photochemistry of these systems demonstrated the following advantages due to the structural confinement: avoiding excited state quenching caused by other chemical species, including aggregated dyes, stabilizing the radical intermediate and tuning the absorption or emission of the guest through electron/energy transfer pathways. The photoinduced dye to redox-active host electron transfer is a new and efficient pathway that is meaningful for chemists to realize and understand many important enzymatic processes and to reveal the secrets of a substance and energy metabolism in biological systems. The confined interactions between the host and the guest have shown fascinating effects of promoting and controlling light-induced chemical transformations.

The Combination of Hydrogen and Methanol Production through Artificial Photosynthesis-Are We Ready Yet?

Because 100 % quantum efficiency for the photosynthetic production of H2 from H2 O under visible illumination has been achieved recently, the oxidation of H2 O to O2 remains the bottleneck to the overall water-splitting reaction. Oxidation of CH4 to CH3 OH might be combined with water reduction instead, so that H2 and CH3 OH chemical fuels can be simultaneously produced through a one-step process under solar illumination. This combination would be a promising approach towards a more sustainable future of chemistry, in which developing different strategies for artificial photosynthesis is of paramount importance. By using free and adsorbed HO. radicals on the semiconductor surface, CH4 can be activated to H3 C. radicals and converted into CH3 OH, respectively, with great selectivity up to 100 %. The present lack of efficient photosynthetic systems for the formation of H2 and CH3 OH from abundant H2 O and CH4 motivates future research for basic science and industrial applications.

Exploitation of microbial biodiversity to engineer efficient photosynthetic system and tolerance to abiotic stresses in plants

Exploitation of microbial biodiversity to engineer efficient photosynthetic system and tolerance to abiotic stresses in plants

Enhanced tolerance of transgenic potato plants expressing choline oxidase in chloroplasts against water stress.

BackgroundGlycinebetaine, whose biosynthesis could be catalyzed by choline oxidase (COD), is an extremely efficient compatible solute for scavenging oxidative stress-inducing molecules and protecting the photosynthetic system in plants. To study the effects of the codA transgene for choline oxidase on the drought resistance and recovery, a transgenic potato cultivar (SC) bearing codA gene and a non-transgenic (NT) control cultivar were raised in pots under moderate and severe drought stress. The experiment was constituted by a two-day-pretreatment with 20% PEG and a four-day-water stress combined with two-day-recovery treatment.ResultsUnder the four-day-water stress, plants were provided with normal water condition, 10% or 20% polyethylene glycol. The results of pretreatment showed an expression of codA gene in transgenic potato and an accumulation of glycine betaine (GB); leaf water potential was higher in SC than in NT. In the stress-recovery-treatment, SC showed stronger antioxidant ability, more efficient photosynthetic system, higher chlorophyll content, lower malondialdehyde content and better recovery from water deficit stress than NT.ConclusionAlthough this work concentrated on the short-term water stress and recover treatments on transgenic potato plants with the over-expression of CodA gene and its control line. The datas shows that the exogenous codA gene provided potato a stronger drought resistance and recovery ability.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-54-30) contains supplementary material, which is available to authorized users.

Peperomia leaf cell wall interface between the multiple hypodermis and crystal-containing photosynthetic layer displays unusual pit fields

Leaves of succulent Peperomia obtusifolia (Piperaceae), and its related species, contain a large multilayered hypodermis (epidermis) subtended by a very small single-layered photosynthetic palisade parenchyma, the latter containing spherical aggregates of crystals called druses. Each druse is in a central vacuole surrounded by chloroplasts. All hypodermal cell walls are thin, except for thick lowermost periclinal walls associated with the upper periclinal walls of the subtending palisade cells. These thick walls display 'quilted' impressions (mounds) formed by many subtending palisade cells. Conspicuous depressions occur in most mounds, and each depression contains what appear to be many plasmodesmata. These depressions are opposite similar regions in adjacent thin palisade periclinal walls, and they can be considered special pit fields that represent thin translucent regions ('windows' or 'skylights'). Druses in the vacuoles of palisade cells occur below these pit field regions and are surrounded by conspicuous cytoplasmic chloroplasts with massive grana oriented perpendicular to the crystals, probably providing for an efficient photosynthetic system under low-intensity light. Leaf clearings and fractures, light microscopy and crossed polarizers, general and histochemical staining, and transmission and scanning electron microscopy were used to examine these structures. Druses in the vacuoles of palisade cells occur below the thin pit field regions in the wall interface, suggesting an interesting physical relationship that could provide a pathway for light waves, filtered through the multiple hypodermis. The light waves pass into the palisade cells and are collected and dispersed by the druses to surrounding chloroplasts with large grana. These results imply an intriguing possible efficient photosynthetic adaptation for species growing in low-light environments, and provide an opportunity for future research on how evolution through environmental adaptation aids plants containing crystals associated with photosynthetic tissues to exist under low-light intensity and with other stresses.

Aspen shoots are carbon autonomous during bud break

Current thinking holds that carbon autonomy of branches in trees is unlikely, particularly during bud break, when the new developing shoots require significant influx of carbon resources from more distant sources. Results from recent studies indicate that the impact of bud break on overall tree reserves might be small. In two studies the independence of flushing shoots from stored carbon reserves and the photosynthesis in developing new leaves and shoots of Populus tremuloides were explored. New developing shoots quickly became a positive carbon source and only a few days into flush, the photosynthetic system of the newly developing shoots was efficient enough to achieve positive carbon gain even at low light levels. Only 14% of the stored shoot reserves, without any mobilization from more distant reserves, were used during bud break and early shoot expansion. Without any underlying stress, shoots of deciduous trees appear to be carbon autonomous during bud break when demand on stored carbon should be the highest. The development of an efficient photosynthetic system in new shoots is critical in the recovery of carbon reserves in aspen. It minimizes the cost of bud break to the overall stored carbon reserves by optimizing the assimilation of carbon in the newly developed leaves, while eliminating the cost for mobilizing carbon reserves from more distant sources. This carbon autonomy of shoots has important implications for the whole tree carbon balance particularly to the non-photosynthetic tissues which functions solely depending on carbon export from the newly developing leaves and shoots.

Construction and maintenance of the optimal photosynthetic systems of the leaf, herbaceous plant and tree: an eco-developmental treatise.

The paper by Monsi and Saeki in 1953 (Japanese Journal of Botany 14: 22-52) was pioneering not only in mathematical modelling of canopy photosynthesis but also in eco-developmental studies of seasonal changes in leaf canopies. Construction and maintenance mechanisms of efficient photosynthetic systems at three different scaling levels--single leaves, herbaceous plants and trees--are reviewed mainly based on the nitrogen optimization theory. First, the nitrogen optimization theory with respect to the canopy and the single leaf is briefly introduced. Secondly, significance of leaf thickness in CO2 diffusion in the leaf and in leaf photosynthesis is discussed. Thirdly, mechanisms of adjustment of photosynthetic properties of the leaf within the herbaceous plant individual throughout its life are discussed. In particular, roles of sugar sensing, redox control and of cytokinin are highlighted. Finally, the development of a tree is considered. Various mechanisms contribute to construction and maintenance of efficient photosynthetic systems. Molecular backgrounds of these ecologically important mechanisms should be clarified. The construction mechanisms of the tree cannot be explained solely by the nitrogen optimization theory. It is proposed that the pipe model theory in its differential form could be a potential tool in future studies in this research area.

Preface: Structure and Function of Plant Canopies

This section comprises a set of papers taken from those presented at a symposium held to commemorate the 50th anniversary of the Monsi-Saeki theory (1953), together with invited papers. The papers describe recent advances in the study of structure and function of plant canopies and are written by former students (and their collaborators) of Professors Monsi and Saeki. The topics cover construction and maintenance of efficient photosynthetic systems at leaf, individual plant and stand level. Canopy structure and function are analysed with respect to optimization and an evolutionarily stable strategy. A new translation of the original paper by Monsi and Saeki (1953) into English has been commissioned and is included in this section.

Electrostatic control of the efficiency of light-induced electron transfer across membranes

The energetics and efficiency of light-induced electron transfer across membranes is examined on a molecular level. It is found that the activation energies that control the efficiency are determined by the solvation energies of the charge-transfer states, the redox potentials of the donors and acceptors, and the dielectric relaxation of the system. The formalism developed allows one to assess the efficiency of any artificial photosynthetic system in terms of its molecular components and their local environment. It is pointed out that the key problem in designing an efficient photosynthetic system is the transfer of a charge through a low dielectric environment and that this problem cannot be overcome by choosing the position of the primary donor and acceptor in the membrane. It is predicted that artificial photosynthetic systems can be optimized by placing the acceptors in polar sites that provide a large effective dielectric constant and low dielectric relaxation and by arranging the acceptors in order of increasing redox potentials. The implication regarding bacterial photosynthesis is discussed.

Energetics of Light‐Induced Charge Separation Across Membranes

AbstractThe efficiency of light induced electron transfer across membranes is examined on a molecular level. The activation energies that determine this efficiency are evaluated by pure electrostatic considerations in terms of the membrane dielectric and the relaxation of the dielectric at the sites of the electron donors and acceptors. These considerations allow one, for the first time, to assess the efficiency of photosynthetic systems in terms of their molecular components. It is demonstrated that a conduction chain of stacked acceptors immersed in a low dielectric membrane cannot be expected to provide an efficient photosynthetic system. On the other hand, efficient photosynthetic systems can be obtained when the acceptors are placed in polar active sites of proteins and arranged in order of increasing redox potentials.

Wirksamkeit der symbiontischen N2-Fixierung der Körnerleguminosen in Abhängigkeit von Rhizobienimpfung, Substrat, N-Düngung und 14C-saccharoselieferung

Cultivation experiments (Mitscherlich-vessels, quartz sand, 15N-labelled soil, 15N-fertilizer) showed, that various strains of Rhizobium lupini (white and yellow lupines) and of Rhizobium leguminosarum (field beans and peas) induced a different N2-fixation of the inoculated plants, the most effective Rhizobium strains being 367a, Cz, T3, 271 (Rh. lupini), and Azotogen (Rh, leguminosarum). Yellow lupines and field bean plants were supplied with N2 from the air considerably better than white lupines and peas after inoculation with the most effective Rhizobium strains. Application of mineral N to the white lupines and peas not only substituted the inhibited N2-fixation, but increased N amounts in the plants. White lupines fixed more N2 under soil conditions than in quartz sand. An experiment with steam-sterilized and 15-labelled soil as a comparative substrate showed, that this finding was mainly caused by an additional Rhizobium infection from the soil. Contrary to field beans and yellow lupines which fix N2 up to ripeness, white lupines and peas finished N2-fixation in the time of flowering. Mineral-N applied at that time was an additional source of N for last-named plants and they utilized it for production of higher protein yields. Continual spraying of white lupine plants with 14C-labelled sucrose solution after the time of flowering caused continuance of N2-fixation up to the stage of ripeness. It is assumed that the cause of this effect was the competition of growing seeds and nodules for the photosynthates. The supply of nodules was inadequate without external sucrose application. Mineral N inhibited the sucrose-induced N2-fixation of white lupine nodules and their consumption of photosynthates. Consequently, the applied 14C was transported into seeds to a larger extent. The investigations allow the following conclusion: Effective N2-fixation requires nodules being a powerful sink for assimilates on the basis of a highly efficient photosynthetic system of the host plant.

Variation of Chloroplast‐associated Processes with Divergent Selections from Zea mays L.1

Associations among chloroplast characteristics were investigated using divergent selections from Zea mays L.; narrow (NL) vs. wide (WL) leaves, two replicates low (LP) vs. high (HP) stalk volume (sixth leaf stage) and golden (g) vs. normal (G) isopopulations. Leaf width selections differed in chlorophyll contents but had similar in vitro rates of ferricyanide reduction and noncyclic photophosphorylation, chloroplast protein levels and rates of net CO2 fixed per mg chlorophyll for three light intensities. The LP selections had inefficient photosynthetic systems relative to HP, while Golden had at least as efficient photosynthetic system as Normal. In contrast, LP selections had 13% and Golden 23% higher ferricyanide reduction and noncyclic photophosphorylation rates than HP and Normal, respectively. Information from in vitro measures was contradictory to that from other sources. Genetically controlled differences for chloroplast protein relative to chlorophyll level were found. Total chloroplast protein (TCP) and a fraction removed by NaOH (CPF) were both highly correlated with ferricyanide reduction rates. While TCP and CPF levels reflected seasonal effects, differences between genotypes for protein levels remained relatively consistent. TCP measure was proposed for population genetic studies to establish whether photochemical properties of chloroplasts have value as selection criteria.

Influence of Temperature on the Growth of Erodium botrys and Trifolium subterraneum1

Temperature effects on the vegetative growth of broadleaf filaree, Erodium botrys (Cav.) Bertol., and subterranean clover, Trijolium subterraneum L., were studied at three diurnal temperature regimes: low (5 to 15 C), medium (10 to 20 C), and high (15 to 25 C). The objective of this study was to evaluate the response of these species to temperatures that reflect the conditions of the annual grassland type during the seedling stage. Chambergrown plants were harvested periodically over a 5‐week period.Filaree was less sensitive to low temperatures and exhibited a temperature optimum between 10 to 20 C and 15 to 25 C, whereas sub clover showed a linear increase in relative growth rate with temperature up to 15 to 25 C.Although sub clover demonstrated a more efficient photosynthetic system, i.e., a greater net assimilation rate, filaree had a higher photosynthetic capacity as shown by a greater leaf area ratio. Filaree partitioned more assimilate into leaf tissue than sub clover which in turn produced more stem and root tissue than filaree. These results indicate that filaree is favored when late fall rains occur along with lower temperatures.

Effect of Sunlight on Sap Concentration of Citrus Leaves

1. Increases in the sap concentration of leaves of Eureka lemon and Valencia orange occur when the leaves are exposed to direct sunlight. 2. The sap of Eureka lemon leaves on exposure to direct sunlight increases its concentration more rapidly than does that of Valencia orange leaves. 3. Increases in sap concentration due to the action of sunlight on the leaves are due entirely to photosynthetic products, the ash of the sap remaining the same under both conditions. 4. A greater percentage of the cross-sectional diameter of the Eureka lemon leaves is occupied by palisade tissue than is found to be the case with the Valencia orange leaves. This, together with the fact that more magnesium is found in the sap of Eureka lemon leaves than in that of Valencia orange leaves, and the more rapid response of leafy lemon cuttings to vegetative propagation, lends support to the view that greater increase in lemon leaf sap concentration in direct sunlight over that of orange leaf sap may be due to a more efficient photosynthetic system. 5. The great variation in sap concentration of citrus leaves brought about by direct sunlight indicates that large errors may result through indiscriminate sampling.