Photosynthetic Oxygen Evolution Research Articles

The open-cubane oxo-oxyl coupling mechanism dominates photosynthetic oxygen evolution: a comprehensive DFT investigation on O-O bond formation in the S4 state.

The dioxygen formation mechanism of biological water oxidation in nature has long been the focus of argument; many diverse mechanistic hypotheses have been proposed. Based on a recent breakthrough in the resolution of the electronic and structural properties of the oxygen-evolving complex in the S3 state, our density functional theory (DFT) calculations reveal that the open-cubane oxo-oxyl coupling mechanism, whose substrates preferably originate from W2 and O5 in the S2 state, emerges as the best candidate for O-O bond formation in the S4 state. This is justified by the overwhelming energetic superiority of this mechanism over alternative mechanisms in both the isomeric open and closed-cubane forms of the Mn4CaO5 cluster; spin-dependent reactivity rooted in variable magnetic couplings was found to play an essential role. Importantly, this oxygen evolution mechanism is supported by the recent discovery of femtosecond X-ray free electron lasers (XFEL), and the origin of the observed structural changes from the S1 to S3 state has been analyzed. In this view, we corroborate the proposed water binding mechanism during S2-S3 transition and correlate the theoretical models with experimental findings from aspects of substrate selectivity according to water exchange kinetics. This theoretical consequence for native metalloenzymes may serve as a significant guide for improving the design and synthesis of biomimetic materials in the field of photocatalytic water splitting.

Sulphur alters chromium (VI) toxicity in Solanum melongena seedlings: Role of sulphur assimilation and sulphur-containing antioxidants

The present study investigates modulation in hexavalent chromium [Cr(VI) 25 μM] toxicity by sulphur (S; 0.5, 1.0 and 1.5 mM S as low (LS), medium (MS) and high sulphur (HS), respectively) in Solanum melongena (eggplant) seedlings. Biomass accumulation (fresh and dry weights), photosynthetic pigments, photosynthetic oxygen evolution and S content were declined by Cr(VI) toxicity. Furthermore, fluorescence characteristics (JIP-test) were also affected by Cr(VI), but Cr(VI) toxicity on photosystem II photochemistry was ameliorated by HS treatment via reducing damaging effect on PS II reaction centre and its reduction side. Enhanced respiration, Cr content and oxidative biomarkers: superoxide radical, hydrogen peroxide, lipid peroxidation and membrane damage were observed under Cr(VI) stress. Though Cr(VI) enhanced adenosine triphasphate sulfurylase (ATPS) and o-acetylserine(thiol)lyase (OASTL), glutathione-S-transferase (GST), glutathione reductase (GR) and ascorbate peroxidase (APX) activity, and content of total glutathione, cysteine and NP-SH, however, their levels/activity were further enhanced by S being maximum with HS treatment. The results show that Cr(VI) toxicity does increase under LS treatment while HS protected Cr(VI)-induced damaging effects in brinjal seedlings. Under HS treatment, in mitigating Cr(VI) toxicity, S assimilation and its associated metabolites such as cysteine, glutathione and NP-SH play crucial role.

Physiological responses of coastal and oceanic diatoms to diurnal fluctuations in seawater carbonate chemistry under two CO<sub>2</sub> concentrations

Abstract. Diel and seasonal fluctuations in seawater carbonate chemistry are common in coastal waters, while in the open-ocean carbonate chemistry is much less variable. In both of these environments, ongoing ocean acidification is being superimposed on the natural dynamics of the carbonate buffer system to influence the physiology of phytoplankton. Here, we show that a coastal Thalassiosira weissflogii isolate and an oceanic diatom, Thalassiosira oceanica, respond differentially to diurnal fluctuating carbonate chemistry in current and ocean acidification (OA) scenarios. A fluctuating carbonate chemistry regime showed positive or negligible effects on physiological performance of the coastal species. In contrast, the oceanic species was significantly negatively affected. The fluctuating regime reduced photosynthetic oxygen evolution rates and enhanced dark respiration rates of T. oceanica under ambient CO2 concentration, while in the OA scenario the fluctuating regime depressed its growth rate, chlorophyll a content, and elemental production rates. These contrasting physiological performances of coastal and oceanic diatoms indicate that they differ in the ability to cope with dynamic pCO2. We propose that, in addition to the ability to cope with light, nutrient, and predation pressure, the ability to acclimate to dynamic carbonate chemistry may act as one determinant of the spatial distribution of diatom species. Habitat-relevant diurnal changes in seawater carbonate chemistry can interact with OA to differentially affect diatoms in coastal and pelagic waters.

Photosynthesis of Oil Palm (Elaeis guineensis)

Oil Palm (Elaeis guineensis) plantations cover more than 107,000km2 in SE-Asia but there is little information on its photosynthetic characteristics. Photosynthesis in seedling, juvenile and adult Oil Palm (6 months, 1–2y and >5y old, respectively) were measured using blue-diode Pulse Amplitude Modulation Fluorometry (PAM). The Absorptance Factor of the leaves (Abt465nm) was measured using a Reflectance Absorptance Transmission (RAT) meter to calculate actual, rather than relative Electron Transport Rates (ETR). Midday measurements in juvenile and adult Oil Palm tree were: maximum quantum yield of Photosystem II (Ymax) in juveniles was about 0.63, Optimum irradiance (Eopt) was ≈300μmolphotonm−2s−1. The maximum ETR (ETRmax) of juvenile plants was 24.06±1.69μmole−m−2s−1: based on 4e−/O2 this is equivalent to a maximum Photosynthetic Oxygen Evolution Rate (POERmax) of 89.21±6.25μmol O2 mg Chl a−1h−1. Adult Oil Palm plants have a Ymax similar to juveniles but Eopt was ≈600μmolphotonm−2s−1. The ETRmax of adult plants was 58.97±2.07μmole−m−2s−1: or POERmax=305.3±10.7μmol O2 mg Chl a−1h−1. Oil Palm is a classic sun plant with high photosynthetic rates at high irradiances. Photosynthetic efficiencies (α0) were high for C3 sun plants: α0 in adult plants (0.272±0.018e− photon−1) was higher than juvenile plants (0.204±0.034e− photon−1) expressed on a leaf surface area basis and on a Chl a basis (1.406±0.093 vs. 0.757 ± 0.124 O2 photon−1m2g Chl a−1). In juvenile and adult plants Eopt, POERmax and α0 tend to maximize about midday. In seedlings, Eopt and POERmax are highest in the early morning but maximum α0 is at about midday. Oil Palms strategically optimize photosynthesis for high irradiances and manipulate their photosynthesis vs. irradiance characteristics during the course of daylight.

Dynamics of Proton Transfer to Internal Water during the Photosynthetic Oxygen-Evolving Cycle.

In photosynthesis, the light-driven oxidation of water is a sustainable process, which converts solar to chemical energy and produces protons and oxygen. To enable biomimetic strategies, the mechanism of photosynthetic oxygen evolution must be elucidated. Here, we provide information concerning a critical step in the oxygen-evolving, or S-state, cycle. During this S3-to-S0 transition, oxygen is produced, and substrate water binds to the manganese-calcium catalytic site. Our spectroscopic and H218O labeling experiments show that this S3-to-S0 step is associated with the protonation of an internal water cluster in a hydrogen-bonding network, which contains calcium. When compared to the protonated water cluster, formed during a preceding step, the S1-to-S2 transition, the S3-to-S0 hydronium ion is likely to be coordinated by additional water molecules. This evidence shows that internal water and the hydrogen bonding network act as a transient proton acceptor at multiple points in the oxygen-evolving cycle.

Comparison of Photoacoustic Signals in Photosynthetic and Nonphotosynthetic Leaf Tissues of Variegated Pelargonium zonale

Green-white variegated leaves of Pelargonium zonale were studied using the photoacoustic method. Our aim was to characterize photosynthetically active green tissue and nonphotosynthetically active white tissue by the photoacoustic amplitude signals. We observed lower stomatal conductance and higher leaf temperature in white tissue than in green tissue. Besides these thermal differences, significantly higher absorbance in green tissue was based on chlorophyll and carotenoids which were absent in white tissue. However, optical properties of epidermal layers of both tissues were equal. The photoacoustic amplitude of white tissue was over four times higher compared to green tissue, which was correlated with lower stomatal conductance. In addition, at frequencies >700 Hz, the significant differences between the photoacoustic signals of green and white tissue were obtained. We identified the photoacoustic signal deriving from photosynthetic oxygen evolution in green tissue, using high intensity of red light modulated at 10 Hz. Moreover, the photoacoustic amplitude of green tissue increased progressively with time which corresponded to the period of induction of photosynthetic oxygen evolution. For the first time, very high frequencies (1 kHz to 5 kHz) were applied on leaf material.

NdhV subunit regulates the activity of type-1 NAD(P)H dehydrogenase under high light conditions in cyanobacterium Synechocystis sp. PCC 6803.

The cyanobacterial NAD(P)H dehydrogenase (NDH-1) complexes play crucial roles in variety of bioenergetic reactions. However, the regulative mechanism of NDH-1 under stressed conditions is still unclear. In this study, we detected that the NDH-1 activity is partially impaired, but the accumulation of NDH-1 complexes was little affected in the NdhV deleted mutant (ΔndhV) at low light in cyanobacterium Synechocystis sp. PCC 6803. ΔndhV grew normally at low light but slowly at high light under inorganic carbon limitation conditions (low pH or low CO2), meanwhile the activity of CO2 uptake was evidently lowered than wild type even at pH 8.0. The accumulation of NdhV in thylakoids strictly relies on the presence of the hydrophilic subcomplex of NDH-1. Furthermore, NdhV was co-located with hydrophilic subunits of NDH-1 loosely associated with the NDH-1L, NDH-1MS′ and NDH-1M complexes. The level of the NdhV was significantly increased at high light and deletion of NdhV suppressed the up-regulation of NDH-1 activity, causing the lowered the photosynthetic oxygen evolution at pH 6.5 and high light. These data indicate that NdhV is an intrinsic subunit of hydrophilic subcomplex of NDH-1, required for efficient operation of cyclic electron transport around photosystem I and CO2 uptake at high lights.

Gas exchange, carbon balance and stomatal traits in wild and cultivated rice (Oryza sativa L.) genotypes

Carbon balancing within the plant species is an important feature for climatic adaptability. Photosynthesis and respiration traits are directly linked with carbon balance. These features were studied in 20 wild rice accessions Oryza spp., and cultivars. Wide variation was observed within the wild rice accessions for photosynthetic oxygen evolution or photosynthetic rate (A), dark (Rd), and light induced respiration (LIR) rates, as well as stomatal density and number. The mean rate of A varied from 10.49 μmol O2 m−2 s−1 in cultivated species and 13.09 μmol O2 m−2 s−1 in wild spp., The mean Rd is 2.09 μmol O2 m−2 s−1 and 2.31 μmol O2 m−2 s−1 in cultivated and wild spp., respectively. Light induced Respiration (LIR) was found to be almost twice in wild rice spp., (16.75 μmol O2 m−2 s−1) compared to cultivated Oryza spp., Among the various parameters, this study reveals LIR and A as the key factors for positive carbon balance. Stomatal contribution towards carbon balance appears to be more dependent on abaxial surface where several number of stomata are situated. Correlation analysis indicates that Rd and LIR increase with the increase in A. In this study, O. nivara (CR 100100, CR 100097), O. rufipogon (IR 103404) and O. glumaepatula (IR104387) were identified as potential donors which could be used in rice breeding program. Co-ordination between gas exchange and patchiness in stomatal behaviour appears to be important for carbon balance and environmental adaptation of wild rice accessions, therefore, survival under harsh environment.

Aplicación de la Técnica Fotoacústica Resuelta en Tiempo al Monitoreo de la Fotosíntesis en Plantas de Lirio Acuático (Eichhornia Crassipes).

We reported about the use of the time resolved photoacoustic technique for the analysis of the photosynthetic oxygen evolution and the energy storage in green plants. We present an application of this technique to the study of the photosynthesis in the aquatic vegetation, usually called aquatic lirium or water hyacinth (Eichhornia Crassipes).

Morphology, growth, biochemical composition and photosynthetic performance of Chlorella vulgaris (Trebouxiophyceae) under low and high nitrogen supplies

Storage triacylglycerol accumulated by oleaginous microalgae have been utilized as optimal feedstock for biodiesel production. Nitrogen limitation is one of the most effective approaches in inducing oil accumulation in microalgae. However, the mechanism underlying this process is not well established. The aim of the present study was to determine changes in morphology, growth, biochemical composition, and photosynthetic performance of Chlorella vulgaris JNU13 under low nitrogen supply (LN, 3.5mM) and high nitrogen supply (HN, 17.6mM). The results showed that LN repressed cell division and cell weight gain. C. vulgaris under HN showed higher lipid levels compared to those subjected to LN. LN showed a decrease in photosynthetic capacity [relative electron transport rate (rETR), photosynthetic oxygen evolution rate (Pn), and utilization efficiency of light energy (α)], ratio of PS I to PS II, dark respiration rate (Rd), and the proportion of z-scheme electron transport pathway. Inversely, LN increased the proportion of the alternative electron transport pathway and non-photochemical quenching (NPQ). The damaged photosystems during limited nitrogen conditions negatively affected lipid accumulation in oleaginous C. vulgaris JNU13. It is therefore essential to maintain a balance between low nitrogen stress and high photosynthetic capacity by regulating the initial nitrogen supply to maximize lipid yield. The results of the present study may be used as a reference for regulating the initial nitrogen supply to enhance oil productivity.

Effects of sodium bicarbonate concentration on growth, photosynthesis, and carbonic anhydrase activity of macroalgae Gracilariopsis lemaneiformis, Gracilaria vermiculophylla, and Gracilaria chouae (Gracilariales, Rhodophyta).

There is potential for bicarbonate to improve crop yields and economic efficiency of marine algae. However, few studies have focused on the effect of bicarbonate on the growth, photosynthesis, and enzyme activity associated with carbon utilization, especially in commercial macroalgae. Here, the addition of bicarbonate (up to 420mg L(-1)) to macroalgal cultures has been evaluated for Gracilariopsis lemaneiformis, Gracilaria vermiculophylla, and Gracilaria chouae with respect to growth rate, photosynthetic activity, carbonic anhydrase activity, and biochemical composition. The results showed that the effects of NaHCO3 on growth, chlorophyll a, phycoerythrin, photosynthetic oxygen evolution, photochemical parameters of PSI and PSII, carbonic anhydrase activity, and nitrogen content were significant (P<0.05) and followed the same pattern in the three species. The parameter values were promoted in lower NaHCO3 concentrations (up to 252 or 336mg L(-1)) and inhibited in higher NaHCO3 concentrations (>336mg L(-1) for Gp. lemaneiformis and>420mg L(-1) for the other two species). Moreover, species-specific differences induced by supplementation with bicarbonate were discovered during culture. Optimal concentrations of NaHCO3 used in this study were 252mg L(-1) for Gp. lemaneiformis and 336mg L(-1) for G. vermiculophylla and G. chouae. These results suggest that an adequate supplementation of sodium bicarbonate is a viable strategy for promoting growth and photosynthetic activity in some macroalgae as well as for improving biochemical composition. The study will help to accelerate the growth rate of algae and improve the quality of thalli, and will also be useful for enhancing the understanding of carbon utilization in macroalgae.

Analysis of triacylglycerol accumulation under nitrogen deprivation in the red alga Cyanidioschyzon merolae.

Triacylglycerol (TAG) produced by microalgae is a potential source of biofuel. Although various metabolic pathways in TAG synthesis have been identified in land plants, the pathway of TAG synthesis in microalgae remains to be clarified. The unicellular rhodophyte Cyanidioschyzon merolae has unique properties as a producer of biofuel because of easy culture and feasibility of genetic engineering. Additionally, it is useful in the investigation of the pathway of TAG synthesis, because all of the nuclear, mitochondrial and plastid genomes have been completely sequenced. We found that this alga accumulated TAG under nitrogen deprivation. Curiously, the amount and composition of plastid membrane lipids did not change significantly, whereas the amount of endoplasmic reticulum (ER) lipids increased with considerable changes in fatty acid composition. The nitrogen deprivation did not decrease photosynthetic oxygen evolution per chlorophyll significantly, while phycobilisomes were degraded preferentially. These results suggest that the synthesis of fatty acids is maintained in the plastid, which is used for the synthesis of TAG in the ER. The accumulated TAG contained mainly 18 : 2(9,12) at the C-2 position, which could be derived from phosphatidylcholine, which also contains this acid at the C-2 position.

A simple indicator for non-destructive estimation of the violaxanthin cycle pigment content in leaves.

The photosynthetic apparatus of higher plants acclimates to irradiance. Among the features which are changing is the pool size of the pigments belonging to the violaxanthin cycle, in which zeaxanthin is formed. In high light grown leaves, the violaxanthin cycle pool size is up to five times larger than in low light. The changes are reversible on a time scale of several days. Since it has been published that violaxanthin cycle pigments do not transfer absorbed energy to chlorophyll, we hypothesized that excitation of chlorophyll fluorescence in the blue spectral region may be reduced in high light-acclimated leaves. Fluorescence excitation spectra of leaves of the Arabidopsis thaliana tt3 mutant showed strong differences between high and low light-acclimated plants from 430 to 520nm. The resulting difference spectrum was similar to carotenoids but shifted by about 20nm to higher wavelengths. A good correlation was observed between the fluorescence excitation ratio F 470/F 660 and the violaxanthin cycle pool size when leaves were acclimated to a range of irradiances. In parallel to the decline of F 470/F 660 with high light acclimation also the quantum yield of photosynthetic oxygen evolution in blue light decreased. The data confirm that violaxanthin cycle carotenoids do not transfer absorbed light to chlorophyll. It is proposed to use the ratio F 470/F 660 as an indicator for the light acclimation status of the chloroplasts in a leaf.

Capsular polysaccharides facilitate enhanced iron acquisition by the colonial cyanobacterium Microcystis sp. isolated from a freshwater lake.

Microcystis sp., especially in its colonial form, is a common dominant species during cyanobacterial blooms in many iron-deficient water bodies. It is still not entirely clear, however, how the colonial forms of Microcystis acclimate to iron-deficient habitats, and the responses of unicellular and colonial forms to iron-replete and iron-deficient conditions were examined here. Growth rates and levels of photosynthetic pigments declined to a greater extent in cultures of unicellular Microcystis than in cultures of the colonial form in response to decreasing iron concentrations, resulting in the impaired photosynthetic performance of unicellular Microcystis as compared to colonial forms as measured by variable fluorescence and photosynthetic oxygen evolution. These results indicate that the light-harvesting ability and photosynthetic capacity of colonial Microcystis was less affected by iron deficiency than the unicellular form. The carotenoid contents and nonphotochemical quenching of colonial Microcystis were less reduced than those of the unicellular form under decreasing iron concentrations, indicating that the colonial morphology enhanced photoprotection and acclimation to iron-deficient conditions. Furthermore, large amounts of iron were detected in the capsular polysaccharides (CPS) of the colonies, and more iron was found to be attached to the colonial Microcystis CPS under decreasing iron conditions as compared to unicellular cultures. These results demonstrated that colonial Microcystis can acclimate to iron deficiencies better than the unicellular form, and that CPS plays an important role in their acclimation advantage in iron-deficient waters.

Physiological Performances of Temperate Vegetables with Response to Chronic and Acute Heat Stress

In face of climate change catastrophes, understanding the thermal limits and optimal physiological thermal window food crop is of particular urgency. This research aims to evaluate: 1) how physiological performances of plant will change with increasing chronic and acute heat stress; 2) if the examined parameters form a hierarchy in terms of thermal tolerance; and 3) the optimal thermal window and critical temperatures of the examined plants with response to chronic and acute heat stress. Six temperate vegetables were subjected to chronic and acute heat stress and a suite of physiological parameters were evaluated. Dose responses were observed in shoot fresh weight, photosynthetic gas exchange, photosynthetic oxygen evolution, electron transfer rate, photo- and non-photochemical quenching with significant drop in performance as early as 28°C for selected species. Conversely, ratio of variable to maximum fluorescence (Fv/Fm) was not affected by heat stress until 46°C in chronic heat stress. Examining the temperature at which a measured parameter’s performance dropped by 50% compared to control (LT50), a distinct hierarchy of the indices was observed for Canasta, recombinant inbred line 141, Lactuca serriola and Lactuca sativa (L. “Salinas”): shoot fresh weight, representing the highest integrated level of photosynthesis was the most sensitive to thermal stress (28°C - 30°C), followed by oxygen evolution (35°C - 45°C) while non-photochemical and photochemical quenching which is subcellular function of stress alleviation had a much higher capacity failure temperature (47°C - 60°C). It is expected that Fv/Fm ratio, a measurement of sub-cellular structural integrity, will approach that of non-photochemical and photochemical quenching, if not exceeding it. By examining the photosynthetic parameters via their hierarchy of biological organization, it can be inferred that plants like Arugula and recombinant inbred line 192 are already operating near their thermal limit and have less energetic investment into heat stress mediation whereas L. serriola prioritizes thermal tolerance at the expense of photosynthesis efficiency.

Influence of the sanosil-induced oxidative stress on the photosynthetic apparatus of different strains of green algae and cyanobacteria

Photosynthetic oxygen evolution (measured by polarographic oxygen rate electrode) and pulse amplitude modulated chlorophyll fluorescence were used to assess the effect of sanosil-induced oxidative stress on photosystem II (PSII) in the green alga Chlorella vulgaris and the cyanobacterium Synechocystis salina isolated from Antarctic and mesophilic environments. This study revealed a relatively stronger influence of sanosil (especially its main component, hydrogen peroxide) on the donor site (oxygen evolving complex) compared to the acceptor side of the PSII in both green algae and cyanobacteria. The inhibition of the oxygen evolution results mainly from a decrease in the fast operating PSII centers. In addition, the obtained data showed that the effects of the oxidative stress on the cyanobacterium and the green alga strongly depend on the antenna size of PSII.

Discerning the effects of photoinhibition and photoprotection on the rate of oxygen evolution in Arabidopsis leaves

Higher plants possess a set of interconnected processes to regulate light harvesting. Non-photochemical quenching of chlorophyll a fluorescence (NPQ) is the fastest process activated to protect the photosystem (PS) II from the absorption of excess light energy. However, damage of PSII reaction centers (RCIIs) is often inevitable, a phenomenon known as photoinhibition. Both NPQ and photoinhibition undermine PSII quantum yield (ΦPSII). Recently, we devised a fluorescence-based methodology that uses the coefficient of photochemical quenching measured in the dark following illumination (qPd) to assess the intactness of RCIIs. This procedure enables to express ΦPSII as a function (ƒ) of NPQ and qPd, ΦPSII=ƒ(NPQ,qPd), thus allowing to efficiently discern between the effects of protective NPQ and photoinhibition upon the efficiency of electron transport. In this study, we addressed the relationship between qPd and ΦPSII measured by photosynthetic oxygen evolution in intact leaves of Arabidopsis. We found a linear correlation between qPd and ΦPSII of oxygen evolution (as well as Fv/Fm). This relates to the fact that qPd reflects the onset of photoinhibition. These results further demonstrate the validity of the qPd parameter and underlying theory in quantitatively assessing PSII efficiency solely by using this effective and simple fluorescence technique.

Artificial Photosynthesis- Progress and Prospects

The Joint Center for Artificial Photosynthesis (JCAP) is the Fuels from Sunlight Energy Innovation Hub established by the US Department of Energy in 2010 to advance research and development on systems that convert sunlight, water, and carbon dioxide into a range of commercially useful fuels. JCAP has adopted an approach in which robust concepts for complete solar-fuels generators motivate basic scientific research targeting the accelerated discovery and integration of necessary components. Through a combination of scientific, engineering, and theoretical modeling approaches, JCAP has discovered novel materials and developed solar water-splitting prototypes that exhibit performance characteristics which were inconceivable just five years ago. As JCAP continues into a second five year term, they will capitalize on its scientific achievements and sophisticated technology development during the initial funding period by focusing on artificial photosynthetic systems that produce carbon-based fuels by reducing carbon dioxide. In this talk, both the accomplishments prospects of artificial photosynthesis will be discussed. The initial five-year funding of JCAP resulted in various accomplishments that will be highlighted in this talk, including: discovery of new methods to protect light absorbing semiconductors from corrosion in aqueous solutions while still maintaining excellent electrical charge conduction to the surface; creation of an innovative high-throughput-experimentation facility with a coordinated pipeline for the rapid preparation, processing, screening, characterization, and data analysis of light absorbers and electrocatalysts; discovery of new mechanisms and materials for electrocatalytic water-splitting reactions, including earth-abundant catalysts with activity as good as those based on rare-earth metals; design, construction and testing of versatile, fully integrated test beds to facilitate the evaluation and optimization of new components and assemblies for solar-fuels generators; comprehensive multiphysics analyses and prototypes for the design of efficient and robust PEC H2 devices; life-cycle and techno-economic assessment of possible PEC systems; and standardization and development of benchmarking protocols for PEC component and device-performance validation. As JCAP moves forward into its second five-year mission, JCAP will create the scientific foundation for a scalable technology that converts carbon dioxide into renewable transportation fuels, under mild conditions, with only sunlight providing the input energy. The approach of JCAP towards meeting this objective will be introduced in this talk including the three pillars of: (1) mechanisms: discovery and understanding of highly selective catalytic mechanisms for carbon dioxide reduction and oxygen evolution operative at mild conditions of temperature and pressure; (2) materials: accelerated discovery of electrocatalytic and photoelectrocatalytic materials and useful light absorber photoelectrodes for the selective, efficient CO2 reduction into hydrocarbon fuels; and (3) prototypes: demonstration, in JCAP testbed prototypes, of artificial photosynthetic carbon dioxide reduction components and oxygen evolution components that exceed natural photosynthesis in efficiency and rival it in selectivity.

Study on the photosynthetic characteristics of a Pyropia haitanensis red mutant cultured under different light intensities

The photosynthetic characteristics of a Pyropia haitanensis red mutant mutated from a wild-type strain using chemical mutagens were studied. The aim was to compare the differences in photosynthetic characteristics between the red mutant and the wild type, and then to analyse the possibility of the red mutant as breeding material. The results indicated that the cytoplasm thickness of the red mutant and the wild type were similar, whereas the cell wall of the red mutant was significantly thinner than that of the wild type. Additionally, the chlorophyll a extract absorption spectra of both strains exhibited no obvious difference, whereas the absorption peaks at 498, 545, and 565 nm (which belong to phycoerythrin, PE) in the phycobiliprotein extract absorption spectra of the red mutant were clearly higher than those of the wild type. The PE content per area of the red mutant thallus was significantly higher than that of the wild type, and the ratios of PE to phycocyanin (PC) and PE to chlorophyll a were significantly higher in the red mutant than in the wild type. The net photosynthetic oxygen evolution rates of the red mutant and wild type cultured under different light intensities demonstrated that the oxygen evolution rates of all samples decreased with increasing light intensities, whereas the oxygen evolution rate of the red mutant was higher than that of the wild type under the same light intensities. The light response curves also indicated that the light-saturated photosynthetic rates (Pmax), light saturation points (LSPs), and light compensation points (LCPs) of both strains decreased to different degrees with increasing light intensities and that the Pmax and LSP values of the red mutant were significantly higher than those of the wild type under identical light intensities. In contrast, there were no obvious differences in the respiration rate (Rd) and in the LCP. The Fv/Fm values of both strains were similar before light treatment, whereas the Fv/Fm of the red mutants after culture under different light intensities (120 and 200 μmol photons m−2 s−1) for 3 days were significantly higher than those values of the wild type. Moreover, ∆F/Fm′ also exhibited a similar variation. Based on these results, the high content of PE in the P. haitanensis red mutant causes a steady red phenotype, and the increase in the PE concentration and the decrease in the thickness of the thallus may enhance its photosynthetic physiological activity. Thus, the red mutant of P. haitanensis may provide good material for Pyropia breeding.

Cyanobacterial diversity in hydrocarbon-polluted sediments and their possible role in bioremediation

The cyanobacterial diversity in crude-oil-contaminated mats and soil sediments from the Guwahati refinery, in Guwahati, India, was studied using a polyphasic approach. Sequencing of the 16S rRNA gene of the isolated cyanobacterial strains and of denaturing gradient gel electrophoresis bands of the environmental samples revealed dominance of the genera Leptolyngbya and Planktothrix and the presence of Tolypothrix sp., Anabaena sp., Oscillatoriales sp., and Arthronema sp. These strains exhibited wide variation in their transferase glutamine synthetase activity and ammonia excretion activity. Treatment of isolates with hydrocarbon sludge caused a sharp decrease in photosynthetic oxygen evolution activity followed by time-dependent recovery, which ranged from 18.6% to 153.1% after 4 h. The CO2 evolution activity remained unaffected or exhibited stimulation after 1% or 2% oil sludge treatment.