Hours Of Illumination Research Articles

The photolysis of flash-frozen dilute hydrogen peroxide solutions

[1] Hydrogen peroxide (HOOH) in ice and snow is an important chemical tracer for the oxidative capacity of past atmospheres. A previous study on the photolysis of HOOH used ice samples made from solutions frozen over the course of minutes, conditions that should result in HOOH present in quasi-liquid layers (QLLs). However, since HOOH in natural snows and ices can also be present in the ice matrix, in this work we studied HOOH photolysis in ice samples prepared by flash freezing very dilute aqueous solutions, to keep HOOH in the ice matrix. In addition, rather than following HOOH photolysis by using an organic probe to scavenge photoformed OH, here we measured changes in HOOH concentrations. Based on initial rates of HOOH photolysis, our resulting quantum yields for OH formation, Φ(OH), in ice range from approximately 0.25 to 0.43 between 238 and 265 K, respectively. These values are up to 50% smaller than previously published values from the QLL HOOH experiments, indicating that HOOH in the ice matrix undergoes slower photolysis. Further, during our experiments the HOOH photolysis rate constant sometimes shows a biphasic behavior, with slower photolysis after several hours of illumination. Using these final rate constants of HOOH decay we derive a lower bound, temperature-independent value for Φ(OH) of 0.29(±0.10). Based on Φ(OH) values from our initial rate measurements, we calculate HOOH lifetimes in polar environments as large as 30 days at the summer solstice, which is too short to allow burial of HOOH beneath the photic zone in the snowpack.

Studies on the Stability of Pt/K<sub>2</sub>La<sub>2</sub>Ti<sub>3</sub>O<sub>10</sub> Photocatalytic Hydrogen Evolution

Pt/K2La2Ti3O10 was prepared by impregnating K2La2Ti3O10 into H2PtCl6 solution. The structure of the photocatalyst was studied by means of XRD, UV-Vis spectroscopy and XPS. And the photocatalytic activities of the samples were examined in a Pyrex reaction cell by splitting methanol solution. The result revealed that Pt/K2La2Ti3O10 photocatalyst showed much higher activity than pure K2La2Ti3O10 and kept a high photocatalytic activity even after 120 hours of illumination. XPS showed that the valence state of Pt was reduced from Ptto Pt0 during the illumination.

Spectroscopic and Functional Characterizations of Cyanobacterium Synechocystis PCC 6803 Mutants on and near the Heme Axial Ligand of Cytochrome b559 in Photosystem II

The functional role of cytochrome (cyt) b(559) in photosystem II (PSII) was investigated in H22K alpha and Y18S alpha cyt b(559) mutants of the cyanobacterium Synechocystis sp. PCC6803. H22K alpha and Y18S alpha cyt b(559) mutant carries one amino acid substitution on and near one of heme axial ligands of cyt b(559) in PSII, respectively. Both mutants grew photoautotrophically, assembled stable PSII, and exhibited the normal period-four oscillation in oxygen yield. However, both mutants showed several distinct chlorophyll a fluorescence properties and were more susceptible to photoinhibition than wild type. EPR results indicated the displacement of one of the two axial ligands to the heme of cyt b(559) in H22K alpha mutant reaction centers, at least in isolated reaction centers. The maximum absorption of cyt b(559) in Y18S alpha mutant PSII core complexes was shifted to 561 nm. Y18S alpha and H22K alpha mutant PSII core complexes contained predominately the low potential form of cyt b(559). The findings lend support to the concept that the redox properties of cyt b(559) are strongly influenced by the hydrophobicity and ligation environment of the heme. When the cyt b(559) mutations placed in a D1-D170A genetic background that prevents assembly of the manganese cluster, accumulation of PSII is almost completely abolished. Overall, our data support a functional role of cyt b(559) in protection of PSII under photoinhibition conditions in vivo.

Preparation of nanocrystalline titania films with different porosity by water-based chemical solution deposition

This study describes the synthesis of nanocrystalline titania layers on silicon and glass substrates by chemical solution deposition, using a water-based citratoperoxo-Ti(IV) precursor solution. The same aqueous solution–gel precursor is used for deposition of, both, thin dense layers by spin-coating and thicker porous layers by tape-casting. In the latter, the precursor solution is modified by the addition of polyvinyl alcohol (PVA), which acts as a thickener and pore-forming agent. Phase composition, film morphology, and the hydrophilic character of the films are studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–VIS transmission measurements, variable angle spectroscopic ellipsometry (VASE), and by contact angle measurements. The thin 180 nm titania film, deposited from the unmodified precursor solution, shows a density of about 96%. Upon ultraviolet illumination, it acquires a highly hydrophilic surface. One hour of illumination is sufficient to obtain a water contact angle of almost 0°. Furthermore, the hydrophilisation process shows to be reversible. Tape-casting and thermal treatment of the modified precursor solution gives rise to the formation of a 500 nm thick, porous, pure anatase film. The nanocrystalline thick film is composed of 20–40 nm particles, and contains clearly defined pores of 20 nm, homogeneously distributed along the surface.

Cytokinin effects on tetrapyrrole biosynthesis and photosynthetic activity in barley seedlings

Cytokinin promotes morphological and physiological processes including the tetrapyrrole biosynthetic pathway during plant development. Only a few steps of chlorophyll (Chl) biosynthesis, exerting the phytohormonal influence, have been individually examined. We performed a comprehensive survey of cytokinin action on the regulation of tetrapyrrole biosynthesis with etiolated and greening barley seedlings. Protein contents, enzyme activities and tetrapyrrole metabolites were analyzed for highly regulated metabolic steps including those of 5-aminolevulinic acid (ALA) biosynthesis and enzymes at the branch point for protoporphyrin IX distribution to Chl and heme. Although levels of the two enzymes of ALA synthesis, glutamyl-tRNA reductase and glutamate 1-semialdehyde aminotransferase, were elevated in dark grown kinetin-treated barley seedlings, the ALA synthesis rate was only significantly enhanced when plant were exposed to light. While cytokinin do not stimulatorily affect Fe-chelatase activity and heme content, it promotes activities of the first enzymes in the Mg branch, Mg protoporphyrin IX chelatase and Mg protoporphyrin IX methyltransferase, in etiolated seedlings up to the first 5 h of light exposure in comparison to control. This elevated activities result in stimulated Chl biosynthesis, which again parallels with enhanced photosynthetic activities indicated by the photosynthetic parameters F(V)/F(M), J (CO2max) and J (CO2) in the kinetin-treated greening seedlings during the first hours of illumination. Thus, cytokinin-driven acceleration of the tetrapyrrole metabolism supports functioning and assembly of the photosynthetic complexes in developing chloroplasts.

Photocatalytic oxidation of methomyl in the presence of semiconducting oxides

The photocatalytic degradation of methomyl, a broad spectrum carbamate insecticide, has been investigated in aqueous heterogeneous solutions containing semiconductor oxides as photocatalysts. It was observed that, in the presence of the catalysts, quantitative degradation of the organic molecule occurs after four hours of illumination. As mineralisation products, CO2 and SO42− ions have been identified, whereas the nitrogen atom forms NH4+ and NO3− ions. Various commercial catalysts were compared with respect to their overall photocatalytic efficiency, while the initial photonic efficiency (ζ) of mineralisation under various experimental conditions have been calculated.

Effects of Lactobacilli and lactose on Salmonella typhimurium colonisation and microbial fermentation in the crop of the young turkey

1. Three experiments were performed to examine the effects of Lactobacilli and lactose on microbial fermentation and Salmonella enterica serovar Typhimurium colonisation in the crop of the young turkey. 2. The following carboxylic acids were detected in the crop ingesta: formic, acetic, butyric, lactic, valeric, caproic, oxalic, phenyl acetic, succinic and fumaric; propionic, isobutyric and isovaleric acids were not detectable. 3. At the beginning of the night, there were considerable quantities of ingesta in the crop of young turkeys. During the scotophase, there were progressive reductions in the contents and pH. Moreover, there were linear increases in the concentration of lactic, valeric and caproic acids (by approximately 7-fold over 8 h). Much smaller changes in crop pH were observed in the study where dietary treatments of Lactobacilli were not included. 4. Chronic addition of lactose or Lactobacilli to the diet exerted modest effects on the carboxylic acid concentration in the crop contents but did not consistently influence colonisation of the crop by Salmonella enterica serovar Typhimurium. 5. Young turkeys confine eating to the hours of illumination (photophase) with a peak in consumption prior to the subjective dusk.

Activity and photoregulated expression of PsPK3

The PsPK3 gene of the garden pea encodes a presumptive protein-serine/threonine kinase whose catalytic domain is closely related to the second messenger-dependent kinases. To demonstrate that PsPK3 is a functional protein kinase, its catalytic domain was expressed in and purified from Escherichia coli for in vitro activity assays. The recombinant catalytic domain autophosphorylated primarily on serines. We found previously that when 6-day-old etiolated pea seedlings are illuminated with continuous white light (WLc), PsPK3 transcript levels decline rapidly within apical buds, reaching their minimum levels within just a few hours of illumination. We asked whether PsPK3 transcript levels changed during seedling development using RNA gel blot analyses of total RNA purified from the apical buds and plumular hooks of seedlings ranging in age from 3 to 7 days. During seedling development in darkness, the amount of PsPK3 mRNA exhibited a modest decline. When etiolated seedlings were exposed to 1 day of WLc, PsPK3 gene expression in hooks was light-responsive even at the earliest stage of seedling development and became more responsive as the seedlings aged. We used antibodies directed against recombinant PsPK3 catalytic domain to ask whether light also regulates the abundance of PsPK3 polypeptides in the bud, hook, and upper portion of the stem of pea seedlings. PsPK3-related polypeptides are present in all three organ systems tested and their abundance is decreased by WLc in the hooks and stems of pea seedlings but not in apical buds. Therefore, the PsPK3 gene demonstrates discoordinate regulation of its polypeptide and mRNA abundances in greening pea seedlings.

Photocatalytic Inactivation of Legionella Pneumophila and an Aerobic Bacteria Consortium in Water over TiO2/SiO2 Fibres in a Continuous Reactor

A continuous photoreactor, working in a total recycle mode and irradiated by a low-pressure Hg lamp, has been used to study the bactericidal effect of a photocatalyst, formed by TiO2 embedded in SiO2 fibres, on Legionella pneumophila and a consortium of common gram-negative aerobic bacteria (Escherichia coli, Klebsiella sp., Pseudomona sp. and Proteus sp.) in water. The kinetic modeling of the inactivation process, carried out with the measured values of viable bacteria concentration at the outlet of photoreactor, evidenced that for each pass inside the photoreactor the ratio between the outlet and inlet cell concentrations was of order of 0.01 for the inactivation of L. pneumophila. For the other aerobic bacteria, which are usually taken as reference in photocatalytic bacteria inactivation studies, this ratio was of order of 0.3 for the first hour of illumination, while upon prolonged irradiation (up to 9 h) this ratio increased to 0.7. Several factors inducing this latter decrease of efficiency are possible, as e.g. competition for photocatalytic attack between microorganisms and organic compounds released by damaged bacteria or photoinduced alteration of a small fraction of still viable bacteria making them less interactive with the photocatalyst. The inactivation mechanism normally proposed for common bacteria involves an initial attack of the photogenerated radicals to the outer membrane; the consequent membrane dispersion allows the radicals to damage the cytoplasmic membrane. The higher lethality of the photocatalytic method observed towards Legionella (in comparison to the other aerobic bacteria) is explained considering that the radicals attack the Legionella secretion system, which is adapted for high virulence and would become activated for and through adhesion to the TiO2 surface. This attack would then be able to inactivate L. pneumophila without dispersing the outer membrane. Apart from this, the water flow through the catalyst fibres can facilitate the bacteria transport towards the anatase surface, and additionally the generated shear stress may help adhesion, at least for some bacteria as E. coli, contributing further to improve the photokilling efficiency; both factors may contribute to the efficiency of this photoreactor configuration.

The photoconductivity of sol–gel derived TiO2 films

TiO2 films on silica substrate were prepared by the sol–gel method. The photoconductivity of these films has been studied in different ambient conditions. The photoconductivity in vacuum is much larger than that in air. In air the photoconductivity exhibits saturation after a short illumination time. In vacuum the maximum current is reached after hours of illumination and is more than three orders of magnitude larger than in air. This effect is attributed to a loss of oxygen adsorbed at the surface. Oxygen is known as electron scavenger, and its removal extends the electron lifetime and results in a much larger saturation photocurrent.

Different kinetics of photoinactivation of photosystem I-mediated electron transport and P700 in isolated thylakoid membranes

Photoinactivation kinetics of photosystem I (PSI)-mediated electron transport rate was compared to that of P700 content at room (22 °C) and low (4 °C) temperatures in isolated spinach thylakoid membranes. The high light treatment was carried out under aerobic and anaerobic conditions. At 22 °C the decrease of electron transport rate showed first order exponential kinetics. The amount of P700 decreased linearly, being less affected in the first hours of illumination. During photoinhibition at 4 °C in the presence of oxygen, the kinetics of inactivation of PSI photochemical activity and the content of P700 were different. It was found that 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) had different protective effect on the electron transport rate and on P700 content at both temperatures. Treatment with high light intensity under N 2 atmosphere had no effect on the electron transport rate or P700 content. The possible degradation of PSI reaction centre proteins was determined using immunoblot methods. In the presence of linear electron transport at 22 °C correlation between formation of toxic hydroxyl radicals and inhibition of oxygen uptake was observed.

Diurnal Fluctuations of Nitrate Uptake and In Vivo Nitrate Reductase Activity in Pima and Acala Cotton

This study was conducted to determine whether diurnal fluctuations of nitrate reductase activity in two cotton species, Pima (Gossypium barbadense L.) and Acala (Gossypium hirsutum L.), are regulated by NO−3 uptake or leaf NO−3 concentration. The two species differ greatly in their N use efficiency. The seedlings were grown for 25 d in nutrient solutions containing 0.05, 0.10 or 1.0 mM NO−3 under a 14‐h light/10‐h dark cycle at 30°C/20°C. Uptake rates were measured by following NO−3 depletion from the uptake solutions at 20°C or 30°C. Nitrate reductase activity (NRA) in fully expanded first true leaves was determined by an anaerobic method in vivo. Upon illumination uptake rates for both species, measured at 30°C, increased until they plateaued in about 5 h and were maintained at that level for the remainder of the light period and the following dark cycle. When measured at 20°C in the dark, however, the uptake rates decreased 25 to 30% for the first 3 h and then remained constant. Leaf NRA increased rapidly during the first hour of illumination, reached a plateau and then decreased after 4 to 6 h of illumination. The decline was more rapid when NRA was assayed in the absence of NO−3 In darkness, NRA levels were low and did not fluctuate. Upon illumination, leaf NO−3 concentration also increased for about 7 h and then decreased gradually. The results indicate that (i) the diurnal rhythm of NO−3 uptake is modulated by temperature rather than by light/dark transitions, and (ii) while the increase in NRA upon illumination may be regulated by NO−3 flux from roots to shoots, the decrease in NRA under prolonged illumination is independent of that flux.

Hypocrellin and hypericin-induced phototoxicity of HL-60 cells: apoptosis or necrosis?

Hypericin and hypocrellin are potential antiviral and antineoplastic agents with multiple modes of light-induced biological activity connected with a production of singlet oxygen and/or excited-state proton transfer and consequent pH drop formation in the drugs environment. In present work light-induced cytotoxicity of hypericin and hypocrellin and mechansim of cell death (apoptosis or necrosis) on human leukemic cell line HL-60 was studied. As a mean for apoptosis detection we used poly (ADP-ribose) polymerase (PARP) as a sensitive marker of early stages of apoptosis. Our results show that exposition of HL-60 cells to hypericin (1 x 10(-5) mol x l(-1)) for 4 hours has no effect on PARP cleavage. However, after 24 and 48 hours of illumination there is evident that hypericin in this concentration cleaved PARP (116 kDa) into two fragments (85 and 25 kDa). Contrary to hypericin, hypocrellin in concentration 1 x 10(-5) mol x l(-1) after 4 hours of illumination cleaved PARP into two fragments typical for apoptosis. In lower concentration (1 x 10(-6) mol x l(-1)) hypocrellin possess also significant cytotoxic activity. Because we detected no fragmentation of PARP in all observed time periods we suggest that cytotoxic effect of hypocrellin in this concentration is due to induction of necrosis. Our results support the hypotesis that the hypericin and hypocrellin has similar mechanism of action and illumination increases cytotoxic effect of both agents.

Genetic deletion of proteins resembling Type IV pilins in Synechocystis sp. PCC 6803: their role in binding or transfer of newly synthesized chlorophyll.

Upon non-denaturing gel electrophoresis of Synechocystis sp. PCC 6803 thylakoid extracts, a Type IV pilin-like protein encoded by open reading frame sll1694 was found in chlorophyll-containing bands. The Synechocystis sp. PCC 6803 genome also encodes two similar open reading frames, sll1695 and slr1456. Even though transcripts of sll1694 and slr1456 could be detected, deletion of the three open reading frames in systems with normal chlorophyll content had no effect. However, Sll1694 was found to affect the rate of chlorophyll synthesis and of the assembly of chlorophyll-binding proteins. In the sll1694/sll1695 deletion mutant in a PS I-less/chlL- background, which is unable to synthesize chlorophyll in darkness, chlorophyll synthesis during the first hours of illumination after dark incubation was 30% slower than in the PS I-less/chlL- strain. Moreover, the biogenesis of chlorophyll-protein complexes with a 77K chlorophyll fluorescence emission maximum at 685 mm was delayed by several hours in this mutant whereas the rate of biogenesis of photosystem II was not significantly affected. Furthermore, results of non-denaturing gel electrophoresis indicated that a chlorophyll-binding complex formed during the early hours of chlorophyll synthesis was altered in stability and mobility upon deletion of the three open reading frames. We propose that the protein encoded by sll1694 is involved in, but is not absolutely required for, delivering chlorophyll to nascent photosystems and antennae.

Photoinduced effects in the Sb2Se3–BaCl2–PbCl2 glasses

Photoinduced optical phenomena in amorphous Sb2Se3–BaCl2–PbCl2 glasses are studied using experimental spectroscopic and theoretical quantum chemical methods. Photoinduced two-photon absorption (TPA) (for λ=10.6 μm) and second harmonic generation (SHG) (for the output wavelengths 5.3 μm) were measured. CO laser (λ=5.5 μm) was used as a source of photoinducing light. We have found that with an increasing CO-laser exposure the SHG maximum output signal increases and achieves its maximum value at CO photon fluence 18×1013 phot./cm2 per pulse after two hours of illumination. The output SHG signal was more than one order less comparing with ZnS crystals in case of its third rank nonlinear optical susceptibility tensor components χ222 (λ=10.6 μm). With decreasing temperature the SHG signal strongly increases within the 26–32 K temperature range. Time-dependent probe-pump measurements show an existence of SHG maximum at time delay about 45 ps. Good correlation between SHG and TPA was observed. Spectral positions of the TPA maxima strongly depend on the photoinducing power. We observed at least two maxima of the TPA: at 26 and 70 ps. We explain this dependence within a framework of the quantum chemical approach taken into account electron-vibration anharmonicity. Coming out from the performed calculations and infrared (IR)-spectroscopy Fourier technique measurements in the spectral region between 100 and 300 cm−1 we have ascertained a key role of Sb–Se fragments in the observed photoinduced effects. We have also compared different existing models of the photoinduced changes. The studied glasses have relatively low nonuniformity through the sample surfaces and can be used as a promising material for picosecond IR laser devices.

Structure and blue-light-responsive transcription of a chloroplast psbD promoter from Arabidopsis thaliana.

We characterized the effects of light on psbD transcription and mRNA levels during chloroplast development in Arabidopsis thaliana. After 6 to 12 hours of illumination of dark-grown seedlings, two psbD mRNAs were detected and their 5' ends were mapped to positions -550 and -190 bp upstream from the psbD translational start codon. Their kinetics of accumulation resembled the accumulation of chloroplast psbA and rbcL mRNAs but differed from the accumulation of the nuclear-encoded Lhcb and Chs mRNAs. A third psbD mRNA with its 5' ends at position -950 accumulated after illumination of > 180 h. The 5' ends of this transcript were mapped to a nucleotide sequence that is highly conserved with functional sequences in the barley (Hordeum vulgare) blue-light-responsive promoter (BLRP). Transcription from the Arabidopsis psbD promoter was 3-fold higher in blue relative to red light, whereas red and blue light affected total chloroplast, rbcL, and 16S rDNA transcription similarly. This study shows that transcription of Arabidopsis psbD is mediated by a BLRP and suggests that psbD genes in other land plants are regulated by a common blue-light-signaling pathway. Isolating the BLRP from Arabidopsis will allow molecular genetic studies aimed at identifying the pertinent photoreceptor and components of this phototransduction pathway.

Cloning of a cDNA that encodes farnesyl diphosphate synthase and the blue-light-induced expression of the corresponding gene in the leaves of rice plants

A cDNA encoding farnesyl diphosphate synthase (FPPS), a key enzyme in isoprenoid biosynthesis, was isolated from a cDNA library constructed from mRNA that had been prepared from etiolated rice ( Oriza sativa L. variety Nipponbare) seedlings after three hours of illumination by a subtraction method. The putative polypeptide deduced from the 1289 bp nucleotide sequence consisted of 353 amino acids and had a molecular mass of 40 676 Da. The predicted amino acid sequence exhibited high homology to those of FPPS from Arabidopsis (73% to type 1, 72% to type 2) and white lupin (74%). Southern blot analysis showed that the rice genome might contain only one gene for FPPS. The highest level of expression of the gene was demonstrated in leaves by RNA blot analysis. Moreover, light, in particular blue light, effectively enhanced expression of the gene.

Stability of Single and Tandem Junction A-Si:H Solar Cells Grown using the ECR Process

ABSTRACTWe report on the fabrication and stability tests of single junction a-Si:H, and tandem junction a-Si:H/a-Si:H solar cells using the ECR process under high hydrogen dilution (H-ECR process). We show that devices with high fill factors can be made using the H-ECR process. We also report on the stability studies of the solar cells under 1 and 2-sun illumination conditions. The solar cells show very little degradation even after 500 hours of illumination under 2 x sunlight illumination.

Photodoping and relaxation of persistent photoconductivity in YBa2Cu3Ox studied byin-situ transport measurements

We report on in-situ resistivity and Hall-effect studies of partially oxygen-depleted YBa2Cu3Ox thin films during white light illumination. The measurements were performed at various temperatures between the superconducting transition and room temperature. At all temperatures the resistivity and the Hall coefficient decreased as a function of the illumination time. The Hall number pH and the Hall mobility μH, calculated within a simple one-band model, showed an increase of pH during the illumination without a saturation. At low temperatures, μH behaved similarly to pH. At 200 K, however, μH became constant after several hours of illumination, while at 260 K and 290 K, we observed a short increase of μH followed by a long-term decrease. From the different time dependences of μH and pH, we conclude that two mechanisms contribute to the photodoping effect. Additionally, we observed that after termination of the illumination at 290 K the photodoped values of pH and μH relaxed with substantially different time constants.

Financial evaluation of SPV lanterns for rural lighting in India

Financial evaluation of solar photovoltaic (SPV) lanterns has been undertaken. The factors influencing the capital as well as the maintenance cost of SPV lantern have been analyzed. Cost per hour of illumination and cost per unit useful energy have been used for comparison of SPV lanterns with other options of rural domestic lighting. The benefits accrued to the user of an SPV lantern have been quantified in terms of the monetary worth of the conventional fuels being saved.