High Light Irradiation Research Articles

CREC Optical-Fibre Sensors for Hydrodynamic Studies in Gas−Solid Fluidized Beds

Optical probes can be employed in dense and dilute fluidized beds. Their application is useful to determine particle volume fraction, bubble velocity, bubble size, and solid segregation in dense-phase fluidized-bed reactors, as well as particle-cluster velocity, size, and shape, in downer/riser units. The CREC-UWO team has developed a unique and miniaturized CREC Optiprobes System (CREC-GS-OPS) equipped with a GRIN (graded refraction index) lens. The GRIN lens creates a small volume of high light irradiation by focusing a laser a few millimetres away from the front of the probe tip. This design minimizes sensor intrusiveness and, as a result, provides trustworthy measurements of hydrodynamic parameters. Through the application of the CREC-GS-OPS, advances have been achieved, leading to (a) the development of a “Y-back” unit with graphite ferrules that protects the optiprobes from fibre-optic stresses and prevents the loss of sensor calibration and (b) the establishment of statistically-based data analysis. It is envisioned that through the introduction of a few design changes, the CREC Optiprobes will be made suitable for high-temperature applications. This will allow the measurement of catalyst flow recirculation (among other measurements), in industrial-scale fluidized-bed catalytic cracking units involving fluidized riser crackers and catalyst regenerators.

High-Proportion Blue Light Irradiation at the End-of-Production Stage Promotes the Biosynthesis and Recycling of Ascorbate in Lettuce.

Ascorbate (AsA), an essential antioxidant for both plants and the human body, plays a vital role in maintaining proper functionality. Light plays an important role in metabolism of AsA in horticultural plants. Our previous research has revealed that subjecting lettuce to high light irradiation (HLI) (500 μmol·m-2·s-1) at the end-of-production (EOP) stage effectively enhances AsA levels, while the optimal light quality for AsA accumulation is still unknown. In this study, four combinations of red (R) and blue (B) light spectra with the ratio of 1:1 (1R1B), 2:1 (2R1B), 3:1 (3R1B), and 4:1 (4R1B) were applied to investigate the biosynthesis and recycling of AsA in lettuce. The results demonstrated that the AsA/total-AsA content in lettuce leaves was notably augmented upon exposure to 1R1B and 2R1B. Interestingly, AsA levels across all treatments increased rapidly at the early stage (2-8 h) of irradiation, while they increased slowly at the late stage (8-16 h). The activity of L-galactono-1,4-lactone dehydrogenase was augmented under 1R1B treatment, which is pivotal to AsA production. Additionally, the activities of enzymes key to AsA cycling were enhanced by 1R1B and 2R1B treatments, including ascorbate peroxidase, dehydroascorbate reductase, and monodehydroascorbate reductase. Notably, hydrogen peroxide and malondialdehyde accumulation increased dramatically following 16 h of 1R1B and 2R1B treatments. In addition, although soluble sugar and starch contents were enhanced by EOP-HLI, this effect was comparatively subdued under the 1R1B treatment. Overall, these results indicated that AsA accumulation was improved by irradiation with a blue light proportion of over 50% in lettuce, aligning with the heightened activities of key enzymes responsible for AsA synthesis, as well as the accrual of hydrogen peroxide. The effective strategy holds the potential to enhance the nutritional quality of lettuce while bolstering its antioxidant defenses.

Characterization of PetM cytochrome b6f subunit 7 domain-containing protein in tomato

Abstract In recent years, multiple advances have been made in understanding the photosynthetic machinery in model organisms. Knowledge transfer to horticultural important fruit crops is challenging and time-consuming due to restrictions in gene editing tools and prolonged life cycles. Here, we characterize a gene encoding a PetM domain-containing protein in tomato. The CRISPR/Cas9 knockout lines of the PetM showed impairment in the chloroplastic electron transport rate (ETR), reduced CO2 assimilation, and reduction of carotenoids and chlorophylls (Chl) under several light conditions. Further, growth-condition-dependent elevation or repression of Chl a/b ratios and de-epoxidation states were identified, underlining possible impairment compensation mechanisms. However, under low light and glasshouse conditions, there were basal levels in CO2 assimilation and ETR, indicating a potential role of the PetM domain in stabilizing the cytochrome b6f complex (Cb6f) under higher light irradiance and increasing its quantum efficiency. This suggests a potential evolutionary role in which this domain might stabilize the site of the Cb6f regulating ratios of cyclic and linear electron transport and its potential importance during the conquest of terrestrial ecosystems during which plants were exposed to higher irradiance. Finally, the results are discussed with regard to metabolism and their implication to photosynthesis from an agronomic perspective.

Redox-mediated activation of ATG3 promotes ATG8 lipidation and autophagy progression in Chlamydomonas reinhardtii.

Autophagy is one of the main degradative pathways used by eukaryotic organisms to eliminate useless or damaged intracellular material to maintain cellular homeostasis under stress conditions. Mounting evidence indicates a strong interplay between the generation of reactive oxygen species and the activation of autophagy. Although a tight redox regulation of autophagy has been shown in several organisms, including microalgae, the molecular mechanisms underlying this control remain poorly understood. In this study, we have performed an in-depth in vitro and in vivo redox characterization of ATG3, an E2-activating enzyme involved in ATG8 lipidation and autophagosome formation, from 2 evolutionary distant unicellular model organisms: the green microalga Chlamydomonas (Chlamydomonas reinhardtii) and the budding yeast Saccharomyces cerevisiae. Our results indicated that ATG3 activity from both organisms is subjected to redox regulation since these proteins require reducing equivalents to transfer ATG8 to the phospholipid phosphatidylethanolamine. We established the catalytic Cys of ATG3 as a redox target in algal and yeast proteins and showed that the oxidoreductase thioredoxin efficiently reduces ATG3. Moreover, in vivo studies revealed that the redox state of ATG3 from Chlamydomonas undergoes profound changes under autophagy-activating stress conditions, such as the absence of photoprotective carotenoids, the inhibition of fatty acid synthesis, or high light irradiance. Thus, our results indicate that the redox-mediated activation of ATG3 regulates ATG8 lipidation under oxidative stress conditions in this model microalga.

Print-Light-Synthesis for Single-Step Metal Nanoparticle Synthesis and Patterned Electrode Production.

The fabrication of thin-film electrodes, which contain metal nanoparticles and nanostructures for applications in electrochemical sensing as well as energy conversion and storage, is often based on multi-step procedures that include two main passages: (i) the synthesis and purification of nanomaterials and (ii) the fabrication of thin films by coating electrode supports with these nanomaterials. The patterning and miniaturization of thin film electrodes generally require masks or advanced patterning instrumentation. In recent years, various approaches have been presented to integrate the spatially resolved deposition of metal precursor solutions and the rapid conversion of the precursors into metal nanoparticles. To achieve the latter, high intensity light irradiation has, in particular, become suitable as it enables the photochemical, photocatalytical, and photothermal conversion of the precursors during or slightly after the precursor deposition. The conversion of the metal precursors directly on the target substrates can make the use of capping and stabilizing agents obsolete. This review focuses on hybrid platforms that comprise digital metal precursor ink printing and high intensity light irradiation for inducing metal precursor conversions into patterned metal and alloy nanoparticles. The combination of the two methods has recently been named Print-Light-Synthesis by a group of collaborators and is characterized by its sustainability in terms of low material consumption, low material waste, and reduced synthesis steps. It provides high control of precursor loading and light irradiation, both affecting and improving the fabrication of thin film electrodes.

Metronomic Photodynamic Therapy with Conjugated Polymer Nanoparticles in Glioblastoma Tumor Microenvironment.

Alternative therapies such as photodynamic therapy (PDT) that combine light, oxygen and photosensitizers (PSs) have been proposed for glioblastoma (GBM) management to overcome conventional treatment issues. An important disadvantage of PDT using a high light irradiance (fluence rate) (cPDT) is the abrupt oxygen consumption that leads to resistance to the treatment. PDT metronomic regimens (mPDT) involving administering light at a low irradiation intensity over a relatively long period of time could be an alternative to circumvent the limitations of conventional PDT protocols. The main objective of the present work was to compare the effectiveness of PDT with an advanced PS based on conjugated polymer nanoparticles (CPN) developed by our group in two irradiation modalities: cPDT and mPDT. The in vitro evaluation was carried out based on cell viability, the impact on the macrophage population of the tumor microenvironment in co-culture conditions and the modulation of HIF-1α as an indirect indicator of oxygen consumption. mPDT regimens with CPNs resulted in more effective cell death, a lower activation of molecular pathways of therapeutic resistance and macrophage polarization towards an antitumoral phenotype. Additionally, mPDT was tested in a GBM heterotopic mouse model, confirming its good performance with promising tumor growth inhibition and apoptotic cell death induction.

Trehalose phosphate phosphatase overexpression for the mitigation of high-light induced stress in Parachlorella kessleri

Parachlorella kessleri is a marine algal species with diverse biofuels and pigments due to its high lipid content. P. kessleri undergo photo-inhibition when grown in outdoor cultivation due to high-light irradiance. Trehalose is a regulatory molecule to relieve stress conditions in P. kessleri. In the present study, over-expression of trehalose phosphate phosphatase (TPP), the trehalose pathway's second gene, was employed in P. kessleri to overcome high-light-induced photo-inhibition. TPP over-expression led to increased trehalose content by 27.23 %. Transformants exhibited enhanced H2O2 scavenging, reduction in chlorophyll b content and enhanced photosynthetic efficiency (Y(II)) as well as regulated non-photochemical quenching (Y(NPQ)) as compared to that of wild type. These combined physiological changes resulted in 35 % and 15 % biomass productivity enhancement at 1000 and 1200 μE m−2 s−1. TPP over-expression was thus associated with improved photosynthetic efficiency and high-light stress resistance in P. kessleri.

Stability Evaluation of Aflatoxin B1 Solution Certified Reference Material via Ultra-High Performance Liquid Chromatography Coupled with High-Resolution Mass Spectrometry

Aflatoxin B1 (AFB1) solution certified reference materials (CRMs) have been widely utilized in the measurements of AFB1 contaminations in foods and agricultural products. It is of great importance to evaluate the stability of AFB1 solution CRMs in different matrices for their practical applications. In this study, the stability of AFB1 solution CRM was investigated and its degradation products under various conditions were elucidated using ultra-high performance liquid chromatography coupled with high-resolution mass spectrometry for the first time. Exposure to high temperatures and UV light irradiation accelerated the degradation of AFB1 solution significantly, and the degradation products were largely dependent on the solvents. Two degradation pathways were proposed based on the degradation products. The addition reaction, oxidation reaction, and modification of the methoxy group are the major processes involved in the degradation of the AFB1 solution. The results of this study indicate that the property value of the acetonitrile solution of AFB1 can be well retained when it is stored at temperatures lower than 60 °C, and the exposure to UV light irradiation is avoided.

The Mediterranean bioconstructor Lithophyllum stictiforme shows adaptability to future warming

Understanding how coralline algae may acclimatize to ocean warming is important to understand their survival over the coming century. Taking advantage of natural differences in temperature conditions between coastal areas in Sardinia (Italy) and between depths, the responses in terms of biological traits to warming of the crustose coralline alga Lithophyllum stictiforme, a key bioconstructor of coralligenous reefs in the Mediterranean, were evaluated in the field by two innovative transplant experiments where translocated specimens were used as controls. Results of the first experiment (algae cross transplanted between a cold and a warm site at two depths, 23 and 34 m) showed that the marginal growth of the alga and production of conceptacles were higher in the cold site, regardless of the treatment (transplant and translocation) and depth. However, growth in thickness in algae transferred from the cold to the warm site was higher at 34 m of depth, where they had a better performance than the local (translocated) algae. Results of the second experiment (algae transplanted from 34 m to 15 m of depth under different light irradiance manipulations) evidenced that the increase in temperature of +4°C was tolerated by thalli transplanted at 15 m, but that thallus growth and conceptacles production was negatively affected by the higher light irradiance. These results suggest an overall good adaptability of L. stictiforme under warmer conditions, even those due to thermocline deepening. Overall, these results encourage consideration of the use of transplants of this bioconstructor in future restoration actions of coralligenous habitats.

Untangling leaf expansion triggers: A new experimental study with Epipremnum aureum (Araceae)

Allomorphic aroid vines exhibit a distinct morphology compared to the typical “sun and shade” leaf pattern. Their leaves exposed to high light irradiance at canopies are up to 30 times larger in area compared to leaves in the forest understory. Growth axis direction, contact with the host, and canopy light are morphogenesis-inducing factors for these aroids. While the first two factors are directly related to growth, the light obtained at canopies is associated with foraging and reproduction. In previous studies, the stimulus of light or the simultaneous application of contact and growth axis direction was not able to induce intense changes in leaf, petiole, and stem dimensions, as seen in nature. In this study, we tested the simultaneous interaction of light intensity, growth axis direction, and contact as inducing factors of morphological shoot development in the allomorphic aroid vine, Epipremnum aureum. An experiment with 60 cuttings was established, which included three growth conditions (horizontal, hanging, and climbing) and two light conditions (low light and high light). After 10 months, the leaf, petiole, and internode dimensions and dry mass allocation were compared. In both the horizontal and hanging treatments, the presence of high light doubled the individual leaf area to approximately 60 cm2. However, when high light was combined with vertical growth and contact stimuli in the climbing treatment, this increase was 20-fold, producing leaves up to 1,000 cm². Dry mass allocation followed the same pattern. This result shows that the enormous leaf area expansion of E. aureum is a synergistic effect of the simultaneous application of light, growth axis direction, and contact. The increase in light interception by wider leaves is an advantage to the maintenance of allomorphic aroid vines in a variable light environment such as in canopies.

Nannochloropsis oceanica (Eustigmatophyceae) mutants resistant to rose bengal demonstrate high tolerance to oxygen

ABSTRACT The genus Nannochloropsis (Eustigmatophyceae), including N. oceanica, has attracted considerable interest, due to its ability to accumulate high levels of lipids. Under large-scale cultivation outdoors, cells are exposed to a combination of high oxygen and light irradiance conditions that may promote photoinhibition, so selecting strains able to tolerate oxidative stress is desirable. Rose bengal (RB) reacts with oxygen to form singlet oxygen in the presence of light. Therefore, RB can be a very useful tool for testing the sensitivity of algae to oxidative stress and thus identify strains capable of photosynthesis under oxidative stress. In this study, two mutants of N. oceanica, RB2 and RB113, which are resistant to high concentrations of rose bengal, were phenotypically characterized for their sensitivity to high oxygen concentrations. Both strains exhibited levels of catalase and ascorbate peroxidase 1.5- and 3-fold higher, respectively, than the wild type. In addition, the synthesis of carotenoids was lower than in the wild type, indicating lower oxidative stress. These results were confirmed by chlorophyll fluorescence measurements, which indicated a lower sensitivity of the photosynthetic apparatus of the mutants, especially of RB2, even in the presence of H2O2. The results support the hypothesis that resistance to rose bengal may also induce resistance to high dissolved oxygen stress. The ability shown by the mutants to perform photosynthesis more efficiently under high oxygen stress than the wild type makes them promising candidates for outdoor cultures.

Transcriptomic and Metabolomic Response to High Light in the Charophyte Alga Klebsormidium nitens.

The characterization of the molecular mechanisms, such as high light irradiance resistance, that allowed plant terrestralization is a cornerstone in evolutionary studies since the conquest of land by plants played a pivotal role in life evolution on Earth. Viridiplantae or the green lineage is divided into two clades, Chlorophyta and Streptophyta, that in turn splits into Embryophyta or land plants and Charophyta. Charophyta are used in evolutionary studies on plant terrestralization since they are generally accepted as the extant algal species most closely related to current land plants. In this study, we have chosen the facultative terrestrial early charophyte alga Klebsormidium nitens to perform an integrative transcriptomic and metabolomic analysis under high light in order to unveil key mechanisms involved in the early steps of plants terrestralization. We found a fast chloroplast retrograde signaling possibly mediated by reactive oxygen species and the inositol polyphosphate 1-phosphatase (SAL1) and 3′-phosphoadenosine-5′-phosphate (PAP) pathways inducing gene expression and accumulation of specific metabolites. Systems used by both Chlorophyta and Embryophyta were activated such as the xanthophyll cycle with an accumulation of zeaxanthin and protein folding and repair mechanisms constituted by NADPH-dependent thioredoxin reductases, thioredoxin-disulfide reductases, and peroxiredoxins. Similarly, cyclic electron flow, specifically the pathway dependent on proton gradient regulation 5, was strongly activated under high light. We detected a simultaneous co-activation of the non-photochemical quenching mechanisms based on LHC-like stress related (LHCSR) protein and the photosystem II subunit S that are specific to Chlorophyta and Embryophyta, respectively. Exclusive Embryophyta systems for the synthesis, sensing, and response to the phytohormone auxin were also activated under high light in K. nitens leading to an increase in auxin content with the concomitant accumulation of amino acids such as tryptophan, histidine, and phenylalanine.

Picophytoplankton in the West Pacific Ocean: A Snapshot.

Marine picophytoplankton have crucial ecological value and make an important contribution to marine primary productivity. While biomass of phytoplankton in general is projected to decline as a result of global warming, picophytoplankton will likely dominate in the future oceans due to their growth advantages in an oligotrophic environment. To better understand the biography of picophytoplankton, we undertook a comprehensive study of the distribution patterns of picophytoplankton, carbon biomass, and Chl a concentrations, etc. based on large-scale sampling in the tropical Western Pacific Ocean. In terms of cellular abundance, Prochlorococcus was the most abundant group (averaging [1.03 ± 0.40] × 104 cells/mL), followed by Synechococcus (averaging [1.31 ± 1.22] × 103 cells/mL) and then picoeucaryote (averaging [4.83 ± 2.84] × 102 cells/mL). The picophytoplankton size-fractionated chlorophyll a (Pico-Chl a) accounted for about 30% of the total Chl a, with Prochlorococcus and picoeukaryotes contributing 41 and 35%, respectively, of the Pico-Chl a-normalized carbon biomass, indicating the ecological importance of picophytoplankton as the primary producers. In terms of biogeographic distribution, the picophytoplankton communities exhibited contrasting patterns. The surface distribution of Prochlorococcus and Synechococcus was concentrated in the low latitude of the 142°E section, while picoeucaryote was more abundant near the 130°E and equator sections. Synechococcus was higher in the shallow layer at 25 m, and it was extremely tolerant of high-light irradiation, while Prochlorococcus and picoeucaryote were distributed in the deep Chlorophyll maximum layer (DCM) (about 100 m). From the carbon-to-Chlorophyll a ratios, which was derived from Prochlorococcus and picoeucaryote population groups, we found that the ratio varied widely, from 0.19 to 75.56, and was highest at the depth of 200 m. Of these, Prochlorococcus had an important contribution. The correlation analysis of environmental factors showed that Prochlorococcus, Synechococcus, and picoeucaryote were negatively correlated with nutrient concentration. We concluded that Prochlorococcus group was dominant in the WPO, both in abundance and biomass, and the various abiotic factors such as temperature, salinity, and nutrient concentrations were closely correlated with the spatial variation in the picophytoplankton community. These findings aid our understanding of how contrasting environmental conditions influence picophytoplankton community and the importance of picophytoplankton in contributing the carbon pool in the oligotrophic ocean.

Heterologous mannitol-1-phosphate dehydrogenase gene over-expression in Parachlorella kessleri for enhanced microalgal biomass productivity

BackgroundMicroalgae have tremendous potential in CO2 sequestration, bioenergy, biofuels, wastewater treatment, and high-value metabolites production. However, large-scale production of microalgae is hampered due to photo-inhibition in outdoor cultivation. Mannitol, as an osmolyte, is known to relieve the stress produced under different abiotic stress conditions during the growth of a photosynthetic organism. ResultsIn the present study, Mannitol-1-phosphate 5-dehydrogenase (Mt1D) was over-expressed to study the effect of mannitol over-production in Parachlorella kessleri under high-light induced stress. Over-expression of Mt1D led to 65% increased mannitol content in the transformed P. kessleri compared to that of wild type. Mannitol transformant demonstrated > 20-fold reduction in reactive oxygen species generation and 15% higher biomass productivity when grown in outdoor cultivation with high-light irradiance of 1200 μmol photons m−2 s−1. ConclusionsThe current study establishes that a higher mannitol concentration provides stress shielding and leads to better acclimatization of transgenic microalgae against high-light generated stress. It also led to reduced ROS generation and improved growth of microalga under study. Thus, overexpression of the Mt1D gene in microalgae can be a suitable strategy to combat high-light stress.

Seasonal diversity of cyanobacteria and new report of Brasilonema sp. colonizing the monuments of Santiniketan and Bishnupur (India)

Cyanobacteria colonize stone monuments around the world. However, the species diversity depends on the substratum and climatic conditions. We documented the seasonal diversity of cyanobacteria in the monuments of Santiniketan and Bishnupur. Though in summer seasons, temperatures on the surface of these monuments go from 45 to 49 °C, we observed the highest diversity of 27 species of cyanobacteria in the summer season. Here, we report for the first time, the presence of Brasilonema sp. from the monuments of Bishnupur and Santiniketan. Bayesian phylogenetic analysis shows it form a strong clade with other Brasilonema sp. along with Scytonema rivulare. We found a reduced form of scytonemin from Brasilonema sp., which might protect against UV and high light. We carried out canonical corresponding analysis (CCA) since we found a significant difference in environmental parameters. Our study shows species like Gloeocapsa sanguinea, Lyngbya arboricola, Scytonema geitleri were positively correlated with environmental parameters. Chroococcus minor is highly influenced by light intensity and relative humidity, whereas Scytonema geitleri was much influenced by light intensity. We also extracted and characterized scytonemin, a UV-absorbing compound from Brasilonema sp. which might be helping it in survival under high light and UV irradiation.

Sunscreen Effect Exerted by Secondary Carotenoids and Mycosporine-like Amino Acids in the Aeroterrestrial Chlorophyte Coelastrella rubescens under High Light and UV-A Irradiation.

The microalga Coelastrella rubescens dwells in habitats with excessive solar irradiation; consequently, it must accumulate diverse compounds to protect itself. We characterized the array of photoprotective compounds in C. rubescens. Toward this goal, we exposed the cells to high fluxes of visible light and UV-A and analyzed the ability of hydrophilic and hydrophobic extracts from the cells to absorb radiation. Potential light-screening compounds were profiled by thin layer chromatography and UPLC-MS. Coelastrella accumulated diverse carotenoids that absorbed visible light in the blue–green part of the spectrum and mycosporine-like amino acids (MAA) that absorbed the UV-A. It is the first report on the occurrence of MAA in Coelastrella. Two new MAA, named coelastrin A and coelastrin B, were identified. Transmission electron microscopy revealed the development of hydrophobic subcompartments under the high light and UV-A exposition. We also evaluate and discuss sporopollenin-like compounds in the cell wall and autophagy-like processes as the possible reason for the decrease in sunlight absorption by cells, in addition to inducible sunscreen accumulation. The results suggested that C. rubescens NAMSU R1 accumulates a broad range of valuable photoprotective compounds in response to UV-A and visible light irradiation, which indicates this strain as a potential producer for biotechnology.

Increasing the performance of Passion fruit (Passiflora edulis) seedlings by LED light regimes

Due to progress in the industrial development of light-emitting diodes (LEDs), much work has been dedicated to understanding the reaction of plants to these light sources in recent years. In this study, the effect of different LED-based light regimes on growth and performance of passion fruit (Passiflora edulis) seedlings was investigated. Combinations of different light irradiances (50, 100, and 200 µmol m−2 s−1), quality (red, green, and blue light-emitting LEDs), and photoperiods (10 h/14 h, 12 h/12 h and 14 h/10 h light/dark cycles) were used to investigate the photosynthetic pigment contents, antioxidants and growth traits of passion fruit seedlings in comparison to the same treatment white fluorescent light. Light irradiance of 100 µmol m−2 s−1 of a 30% red/70% blue LED light combination and 12 h/12 h light/dark cycles showed the best results for plant height, stem diameter, number of leaves, internode distance, and fresh/dry shoot/root weights. 14 h/10 h light/dark cycles with the same LED light combination promoted antioxidant enzyme activities and the accumulation of phenols and flavonoids. In contrast, lower light irradiance (50 µmol m−2 s−1) had negative effects on most of the parameters. We conclude that passion fruit seedlings' optimal performance and biomass production requires long and high light irradiances with a high blue light portion.

Regulation of ascorbate accumulation and metabolism in lettuce by end-of-production high light irradiation provided by red and blue LEDs

Increasing the L-ascorbate (AsA) content of vegetables is very important for improving plant quality in greenhouses and plant factories because AsA is an antioxidant that is essential for the proper function of plants and the human body. End-of-production (EOP) high light irradiation is an economical preharvest practice for improving product quality. Here, we studied the dynamic responses of the AsA pool and AsA metabolism in lettuce exposed to EOP high light irradiation (300, 400, and 500 μmol m−2·s−1) from red and blue LEDs over a 16-h time course. Compared to the control (200 μmol m−2·s−1), the content of AsA and total AsA (T-AsA) in lettuce leaves significantly increased after 8 h of high light irradiation, and the contents of AsA and T-AsA increased by 42.4 % and 36.9 %, respectively, under 500 μmol m−2·s−1 irradiation. Transcript levels of the AsA metabolism-related genes GME, GGP, GPP, GLDH, APX, MDHAR1, MDHAR2, DHAR1, DHAR2, and GR were upregulated under higher light. Likewise, the activities of AsA-related enzymes (GLDH, APX, DHAR, and GR) increased under 500 μmol m−2·s−1. The expression of genes (GGP, GPP, GLDH, MDHAR1, MDHAR2, DHAR1, DHAR2, and GR) was more sensitive to high light irradiation in AsA metabolism. Both high light intensity and long irradiation time increased the soluble sugar content. Moreover, high light intensity (500 μmol m−2·s−1) increased the content of H2O2, O2*−, and MDA in lettuce leaves, especially at 16 h. In conclusion, EOP high light increased AsA levels by upregulating the expression of genes and the activity of enzymes in AsA metabolism. The increase in soluble sugar availability and the signaling of reactive oxygen species also contributed to AsA accumulation. We therefore recommend 8 h of high light (500 μmol m−2·s−1) irradiation before harvest to increase the AsA content of lettuce.

Thymidylate kinase (TMK) of the photosynthetic, nitrogen-fixing cyanobacterium Nostoc sp. strain PCC7120: Biophysical, biochemical and physiological characterisation

Thymidylate kinase (TMK/TMPK) is an important enzyme in DNA biosynthesis and catalyses the conversion of dTMP to dTDP. Due to its therapeutic potential, the focus has been on characterizing the TMK proteins of pathogens and human origin, with very little information available on the TMK proteins of photosynthetic organisms and agriculturally important nitrogen-fixing organisms. In this work we report the characterisation of TMK in an evolutionarily ancient organism, cyanobacteria. The TMK protein of the photosynthetic, nitrogen-fixing cyanobacterium Nostoc PCC7120 (AnTMK) was found to have low conformational stability, which related to its low Tm of ~46 °C confirmed by Differential Scanning Fluorimetry (DSF) and Differential Scanning Calorimetry (DSC) techniques. The AnTMK protein exhibited substrate specificity for dTMP and ATP with Km of 20.74 ± 1.47 μM and 20.17 ± 2.96 μM respectively. The enzyme kinetics data and the positive co-operativity observed between dTMP and ATP binding correlated well with the data obtained from Isothermal Titration Calorimetry (ITC). Homology model of the enzyme suggested that the binding mode of substrate nucleotides to the enzyme is conserved. When overexpressed constitutively in Nostoc PCC7120 (Antmk+), it supported faster growth measured in terms of chlorophyll a content under normal growth conditions, but exhibited lower photosynthetic efficiency. Compared to the vector control recombinant Nostoc AnpAM, the Antmk + cells exhibited higher photoinhibition at higher light irradiance with more open reaction centres and lower dissipation of heat, indicative of damage to photosynthetic machinery. This indicated that the TMK is likely to have a significant role in photosynthetic organisms.

Synergistic dynamics of critical cofactors effectuates fuel relevant metabolic profile of Scenedesmus sp.: Targeting cleaner energy production

Microalgae based biofuel is dictated to a great extent by certain synergistic interactions between critical nutrients as well as the quality and quantity of light energy available. For latitude regions with high light irradiance for a greater part of year, it is important to optimize the proportions of critical nutrients for microalgae species to display a suitable metabolic profile and not loose advantage when total light energy input increases. In this study, the conjunct impact of light intensity using white LED, together with photoperiod and nutrients (nitrate, phosphate and glucose) depleted and replete conditions on energy storage metabolites and fuel characteristics of Scenedesmus sp. were investigated under a mixotrophic growth regime. Results show that Scenedesmus sp. could efficiently exploit even very intense light, for longer duration (216 μmolm−2s−1 at 16:8 light: dark photoperiod) in presence of 1.5 g/L of sodium nitrate, 0.04 g/L of di-sodium hydrogen phosphate and 5 g/L of glucose (G5N1.5P0.04) to produce a biomass of 1782.4 ± 56.8 μg/mL with a specific growth rate of 0.2 ± 0.007 day−1. High light intensity (216 μmolm−2s−1) and organic carbon at 16:8 light: dark photoperiod (L16:D8) led to increased synthesis of carbohydrate content in the absence of nitrate and phosphate (1924.8 ± 128.6 μg/mg at G5N0P0), increased TFA in the absence of nitrate (59.5 μg/mg at G5N0P0.04) and high lipid content (154.1 ± 7.7 μg/mg at G5N1.5P0.04) without obliterating growth. Certain vital properties that determine the biodiesel quality were computed and compared to the parallel parameters put forth by European and American biodiesel norms. These results stand to be a baseline for sustainable algal bio-refinery and create futuristic vistas for further evaluation of Scenedesmus sp. for bio-energy applications in countries like India having tropical climate with high solar incoming radiation for a greater part of the year.