Onset Of Illumination Research Articles

The interplay of post-translational protein modifications in Arabidopsis leaves during photosynthesis induction.

Diurnal dark to light transition causes profound physiological changes in plant metabolism. These changes require distinct modes of regulation as a unique feature of photosynthetic lifestyle. The activities of several key metabolic enzymes are regulated by light-dependent post-translational modifications (PTM) and have been studied at depth at the level of individual proteins. In contrast, a global picture of the light-dependent PTMome dynamics is lacking, leaving the response of a large proportion of cellular function undefined. Here, we investigated the light-dependent metabolome and proteome changes in Arabidopsis rosettes in a time resolved manner to dissect their kinetic interplay, focusing on phosphorylation, lysine acetylation, and cysteine-based redox switches. Of over 24 000 PTM sites that were detected, more than 1700 were changed during the transition from dark to light. While the first changes, as measured 5 min after onset of illumination, occurred mainly in the chloroplasts, PTM changes at proteins in other compartments coincided with the full activation of the Calvin-Benson cycle and the synthesis of sugars at later timepoints. Our data reveal connections between metabolism and PTM-based regulation throughout the cell. The comprehensive multiome profiling analysis provides unique insight into the extent by which photosynthesis reprograms global cell function and adds a powerful resource for the dissection of diverse cellular processes in the context of photosynthetic function.

Real-time laser ultrasonic monitoring of laser-induced thermal processes

Intra- and inter-layer integrity of components fabricated with advanced manufacturing techniques, such as laser powder bed fusion, is dependent upon rapid heating, melting, and solidification processes. There is a need for new techniques to provide in situ feedback of these processes. Here a laser-based ultrasonic technique to probe thermal effects induced by a high-power continuous wave laser in titanium samples is described. Numerical simulations were performed to show that, for a spatially uniform heating beam, laser-induced surface acoustic waves are strongly influenced by surface heating conditions, are dispersive in the case of rapid heating, and that an abrupt velocity reduction happens upon the onset of surface melting. Furthermore, laser-based ultrasound experimental results which monitor the transient change of surface wave travel time associated with high power laser surface heating are provided. A pulsed laser is used to generate high frequency surface acoustic waves that propagate through the laser-heated region and are detected using a photorefractive crystal-based interferometer. Qualitative agreement is observed between theory and experiment with both showing a rapid reduction in the surface wave velocity at the onset of illumination and further decrease in surface wave velocity associated with melting. It is demonstrated that changes in the surface wave velocity can be used to track local heating and detect the onset of surface melting in real time.

Interactions Between Carbon Metabolism and Photosynthetic Electron Transport in a Chlamydomonas reinhardtii Mutant Without CO2 Fixation by RuBisCO.

A Chlamydomonas reinhardtii RuBisCO-less mutant, ΔrbcL, was used to study carbohydrate metabolism without fixation of atmospheric carbon. The regulatory mechanism(s) that control linear electron flow, known as “photosynthetic control,” are amplified in ΔrbcL at the onset of illumination. With the aim to understand the metabolites that control this regulatory response, we have correlated the kinetics of primary carbon metabolites to chlorophyll fluorescence induction curves. We identify that ΔrbcL in the absence of acetate generates adenosine triphosphate (ATP) via photosynthetic electron transfer reactions. Also, metabolites of the Calvin Benson Bassham (CBB) cycle are responsive to the light. Indeed, ribulose 1,5-bisphosphate (RuBP), the last intermediate before carboxylation by Ribulose-1,5-bisphosphate carboxylase-oxygenase, accumulates significantly with time, and CBB cycle intermediates for RuBP regeneration, dihydroxyacetone phosphate (DHAP), pentose phosphates and ribose-5-phosphate (R5P) are rapidly accumulated in the first seconds of illumination, then consumed, showing that although the CBB is blocked, these enzymes are still transiently active. In opposition, in the presence of acetate, consumption of CBB cycle intermediates is strongly diminished, suggesting that the link between light and primary carbon metabolism is almost lost. Phosphorylated hexoses and starch accumulate significantly. We show that acetate uptake results in heterotrophic metabolism dominating phototrophic metabolism, with glyoxylate and tricarboxylic acid (TCA) cycle intermediates being the most highly represented metabolites, specifically succinate and malate. These findings allow us to hypothesize which metabolites and metabolic pathways are relevant to the upregulation of processes like cyclic electron flow that are implicated in photosynthetic control mechanisms.

Impaired photoprotection in Phaeodactylum tricornutum KEA3 mutants reveals the proton regulatory circuit of diatoms light acclimation.

Summary Diatoms are successful phytoplankton clades able to acclimate to changing environmental conditions, including e.g. variable light intensity. Diatoms are outstanding at dissipating light energy exceeding the maximum photosynthetic electron transfer (PET) capacity via the nonphotochemical quenching (NPQ) process. While the molecular effectors of NPQ as well as the involvement of the proton motive force (PMF) in its regulation are known, the regulators of the PET/PMF relationship remain unidentified in diatoms.We generated mutants of the H+/K+ antiporter KEA3 in the model diatom Phaeodactylum tricornutum.Loss of KEA3 activity affects the PET/PMF coupling and NPQ responses at the onset of illumination, during transients and in steady‐state conditions. Thus, this antiporter is a main regulator of the PET/PMF coupling. Consistent with this conclusion, a parsimonious model including only two free components, KEA3 and the diadinoxanthin de‐epoxidase, describes most of the feedback loops between PET and NPQ.This simple regulatory system allows for efficient responses to fast (minutes) or slow (e.g. diel) changes in light environment, thanks to the presence of a regulatory calcium ion (Ca2+)‐binding domain in KEA3 modulating its activity. This circuit is likely tuned by the NPQ‐effector proteins, LHCXs, providing diatoms with the required flexibility to thrive in different ocean provinces.

Global proteomic response of unicellular cyanobacterium Synechocystis sp. PCC 6803 to fluctuating light upon CO2 step-down.

Photosynthetic cyanobacteria are exposed to rapid changes in light intensity in their natural habitats, as well as in photobioreactors. To understand the effects of such fluctuations on Synechocystis sp. PCC 6803, the global proteome of cells grown under a fluctuating light condition (low background light interrupted with high light pulses) was compared to the proteome of cells grown under constant light with concomitant acclimation of cells to low CO2 level. The untargeted global proteome of Synechocystis sp. PCC 6803 was analyzed by data-dependent acquisition (DDA), which relies on the high mass accuracy and sensitivity of orbitrap-based tandem mass spectrometry. In addition, a targeted selected reaction monitoring (SRM) approach was applied to monitor the proteomic changes in a strain lacking flavodiiron proteins Flv1 and Flv3. This strain is characterized by impaired growth and photosynthetic activity under fluctuating light. An obvious reprogramming of cell metabolism was observed in this study and was compared to a previous transcriptional analysis performed under the same fluctuating light regime. Cyanobacterial responses to fluctuating light correlated at mRNA and protein levels to some extent, but discrepancies indicate that several proteins are post-transcriptionally regulated (affecting observed protein abundances). The data suggest that Synechocystis sp. PCC 6803 maintain higher nitrogen assimilation, serving as an electron valve, for long-term acclimation to fluctuating light upon CO2 step-down. Although Flv1 and Flv3 are known to be crucial for the cells at the onset of illumination, the flavodiiron proteins, as well as components of carbon assimilation pathways, were less abundant under fluctuating light.

Near-Infrared Light Increases Functional Connectivity with a Non-thermal Mechanism.

Although techniques for noninvasive brain stimulation are under intense investigation, an approach that has received limited attention is transcranial photobiomodulation (tPBM), the delivery of near-infrared light to the brain with a laser or light-emitting diode directed at the scalp. Here we employed functional magnetic resonance imaging to measure the blood-oxygenation-level–dependent signal in n = 20 healthy human participants while concurrently stimulating their right frontal pole with a near-infrared laser. Functional connectivity with the illuminated region increased by up to 15% during stimulation, with a quarter of all connections experiencing a significant increase. The time course of connectivity exhibited a sharp rise approximately 1 min after illumination onset. Brain-wide connectivity increases were also observed, with connections involving the stimulated hemisphere showing a significantly larger increase than those in the contralateral hemisphere. We subsequently employed magnetic resonance thermometry to measure brain temperature during tPBM (separate cohort, n = 20) and found no significant temperature differences between active and sham stimulation. Our findings suggest that near-infrared light synchronizes brain activity with a nonthermal mechanism, underscoring the promise of tPBM as a new technique for stimulating brain function.

Redox-regulation of mitochondrial metabolism through thioredoxin o1 facilitates light induction of photosynthesis

ABSTRACTDespite the well-known biochemistry of the major pathways involved in central carbon and amino acid metabolism, there are still gaps regarding their regulation or regulatory interactions. Recent research demonstrated the physiological significance of the mitochondrial redox machinery, particularly thioredoxin o1 (TRXo1), for proper regulation of the tricarboxylic acid cycle, components of the mitochondrial electron transport chain and photorespiration. These findings imply that TRXo1 regulation contributes to the metabolic acclimation toward changes in the prevailing environmental conditions. Here, we analyzed if TRXo1 is involved in the light induction of photosynthesis. Our results show that the trxo1 mutant activates CO2 assimilation rates to a significantly lower extend than wild type in response to short-term light/dark changes. Metabolite analysis suggests that activation of glycine-to-serine conversion catalyzed through glycine decarboxylase in conjunction with serine hydroxymethyltransferase in trxo1 is slowed down at onset of illumination. We propose that redox regulation via TRXo1 is necessary to allow the rapid induction of mitochondrial steps of the photorespiratory cycle and, in turn, to facilitate light-induction of photosynthesis.

Immunocytochemical Labeling of Rhabdomeric Proteins in Drosophila Photoreceptor Cells Is Compromised by a Light-dependent Technical Artifact.

Drosophila photoreceptor cells are employed as a model system for studying membrane protein transport. Phototransduction proteins like rhodopsin and the light-activated TRPL ion channel are transported within the photoreceptor cell, and they change their subcellular distribution in a light-dependent way. Investigating the transport mechanisms for rhodopsin and ion channels requires accurate histochemical methods for protein localization. By using immunocytochemistry the light-triggered translocation of TRPL has been described as a two-stage process. In stage 1, TRPL accumulates at the rhabdomere base and the adjacent stalk membrane a few minutes after onset of illumination and is internalized in stage 2 by endocytosis after prolonged light exposure. Here, we show that a commonly observed crescent shaped antibody labeling pattern suggesting a fast translocation of rhodopsin, TRP, and TRPL to the rhabdomere base is a light-dependent antibody staining artifact. This artifact is most probably caused by the profound structural changes in the microvillar membranes of rhabdomeres that result from activation of the signaling cascade. By using alternative labeling methods, either eGFP-tags or the self-labeling SNAP-tag, we show that light activation of TRPL transport indeed results in fast changes of the TRPL distribution in the rhabdomere but not in the way described previously.

Analyzing both the fast and the slow phases of chlorophyll a fluorescence and P700 absorbance changes in dark-adapted and preilluminated pea leaves using a Thylakoid Membrane model.

The dark-to-light transitions enable energization of the thylakoid membrane (TM), which is reflected in fast and slow (OJIPSMT or OABCDE) stages of fluorescence induction (FI) and P700 oxidoreduction changes (ΔA810). A Thylakoid Membrane model (T-M model), in which special emphasis has been placed on ferredoxin-NADP+-oxidoreductase (FNR) activation and energy-dependent qE quenching, was applied for quantifying the kinetics of FI and ΔA810. Pea leaves were kept in darkness for 15min and then the FI and ΔA810 signals were measured upon actinic illumination, applied either directly or after a 10-s light pulse coupled with a subsequent 10-s dark interval. On the time scale from 40 µs to 30s, the parallel T-M model fittings to both FI and ΔA810 signals were obtained. The parameters of FNR activation and the buildup of qE quenching were found to differ for dark-adapted and preilluminated leaves. At the onset of actinic light, photosystem II (PSII) acceptors were oxidized (neutral) after dark adaptation, while the redox states with closed and/or semiquinone QA(-)QB(-) forms were supposedly generated after preillumination, and did not relax within the 10s dark interval. In qE simulations, a pH-dependent Hill relationship was used. The rate constant of heat losses in PSII antenna kD(t) was found to increase from the basic value kDconst, at the onset of illumination, to its maximal level kDvar due to lumenal acidification. In dark-adapted leaves, a low value of kDconst of ∼2×106s-1 was found. Simulations on the microsecond to 30s time scale revealed that the slow P-S-M-T phases of the fluorescence induction were sensitive to light-induced FNR activation and high-energy qE quenching. Thus, the corresponding time-dependent rate constants kD(t) and kFNR(t) change substantially upon the release of electron transport on the acceptor side of PSI and during the NPQ development. The transitions between the cyclic and linear electron transport modes have also been quantified in this paper.

Hybrid Plasmonic and Pyroelectric Harvesting of Light Fluctuations

AbstractState‐of‐the‐art solar energy harvesting systems based on photovoltaic technology require constant illumination for optimal operation. However, weather conditions and solar illumination tend to fluctuate. Here, a device is presented that extracts electrical energy from such light fluctuations. The concept combines light‐induced heating of gold nanodisks (acting as plasmonic optical nanoantennas), and an organic pyroelectric copolymer film (poly(vinylidenefluoride‐co‐trifluoroethylene)), that converts temperature changes into electrical signals. This hybrid device can repeatedly generate current pulses, not only upon the onset of illumination, but also when illumination is blocked. Detailed characterization highlights the key role of the polarization state of the copolymer, while the copolymer thickness has minor influence on performance. The results are fully consistent with plasmon‐assisted pyroelectric effects, as corroborated by combined optical and thermal simulations that match the experimental results. Owing to the tunability of plasmonic resonances, the presented concept is compatible with harvesting near infrared light while concurrently maintaining visible transparency.

Microstructure and Photoelectric Response of Gold Nanocrystalline on TiO2 Nanotube Arrays

In this paper, we report photoelectrical response of gold nanocrystalline on TiO2 nanotubes (TNTs) with Au morphology ranging from nanoparticles, thin nanoring to thick nanoring. The gold nanocrystallines are loaded on the TNT by the facile magnetron sputtering technique. Compared with pristine TNT, the gold-decorated TNTs have shown obvious light absorption at wavelength of 380–850 nm as well as dependence of surface plasmonic resonance (SPR) on Au morphology. Photocurrent response under white light illumination presents around 4 times enhancement on all gold-decorated nanotubes at an applied voltage of 0.2 V. Transient current measurement reveals different ramping up behavior on nanoparticles and nanoring-coated TNTs at the onset of illumination. Full-field electromagnetic wave simulation based on finite element analysis (FEA) indicates that the shifting of SPR peaks is a joint effect of the size/aspect ratio, morphology, and amount of the nanocrystalline Au. Meanwhile, the FEA indicates that instant cu...

Optogenetic termination of atrial fibrillation in mice.

The primary goal in the treatment of symptomatic atrial fibrillation/flutter (AF) is to restore sinus rhythm by cardioversion. Electrical shocks are highly effective, but have to be applied under analgo-sedation and can further harm the heart. In order to develop a novel pain-free and less harmful approach, we explored herein the optogenetic cardioversion by light-induced depolarization. Hearts from mice expressing Channelrhodopsin-2 (ChR2) and the AF-promoting loss-of-function Connexin 40 Ala96Ser mutation were explanted and perfused with low K+ Tyrode's solution and an atrial KATP-channel activator. This new protocol shortened atrial refractoriness as well as slowed atrial conduction and thereby enabled the induction of sustained AF. AF episodes could be terminated by epicardial illumination of the atria with focussed blue light (470 nm, 0.4 mW/mm2) with an efficacy of ∼97% (n = 17 hearts). In > 80% of cases, light directly terminated the AF episode with onset of illumination. Because similar illumination intensity was able to locally inhibit atrial activity, we propose that a light-induced block of electrical activity is responsible for reliable AF termination. The success rate was strongly depending on the illuminated area, applied light intensity and duration of illumination. Importantly, we were also able to demonstrate optogenetic termination of AF in vivo, using epicardial illumination through the open chest (n = 3 hearts). To point towards a translational potential, we systemically injected an adeno-associated virus to express ChR2 in wild type hearts. After 6-8 months, we found robust ChR2 expression in the atria, enabling light-mediated AF termination in six of seven mice tested. We provide the first evidence for optogenetic termination of atrial tachyarrhythmia in intact hearts from transgenic as well as wild type mice ex and in vivo. Thus, this report could lay the foundation for the development of implantable devices for pain-free termination of AF.

The effect of initial stomatal opening on the dynamics of biochemical and overall photosynthetic induction

Initial stomatal conductance at onset of illumination and lag times before stomata start to open in response to light are decisive for the whole course of photosynthetic induction. Neglecting these effects can reverse results when comparing induction parameters within and between species. We analyzed stomatal behaviors, the role of initial stomatal conductance (at onset of light, g ini), and contemporaneous effects on two types of photosynthetic induction, namely “overall” (stomatal and mesophyll effects included) and “biochemical induction” (mainly RuBisCO activity). Studies were performed in sun leaves of four species (Alnus glutinosa (L.) Gaertn., Betula pubescens Ehrh., Fagus sylvatica L., and Helianthus annuus L.) differing in shade-tolerance: A species-specific g ini-threshold, namely g ini(crit), was found, being decisive for time courses of induction. When g ini was above g ini(crit), induction half-times (t 50%) were reached within 5 min, almost completely independent of stomatal limitations, and both induction types did not differ between species. Large variations in t 50% (4–36 min) were observed when g ini < g ini(crit). These correlated linearly with lag times before onset of stomatal opening in response to light (t lag). t lag is generally the longer the lower g ini. Total overall and total biochemical induction correlated highly significantly with velocities of stomatal opening. Different induction times between species occurred as a result of stomatal behavior rather than photosynthetic parameters. Any induction process is initially more limited by the biochemical component. When g ini < g ini(crit), this biochemical limitation shifts towards stomata-dominated limitation at a lower induction state. Consequentially, stomata limit the induction process over most of the induction course. When g ini > g ini(crit) and stomata open fast, then induction is (almost) completely dominated by biochemical limitations and proceeds much faster. This study confirms the very important role of g ini(crit) in photosynthetic induction irrespective of species and discusses implications for modeling.

Analysis of Photoprotection and Apparent Non-photochemical Quenching of Chlorophyll Fluorescence in Tradescantia Leaves Based on the Rate of Irradiance-Induced Changes in Optical Transparence.

The kinetics of irradiation-induced changes in leaf optical transparence (ΔT) and non-photochemical quenching (NPQ) of chlorophyll fluorescence in Tradescantia fluminensis and T. sillamontana leaves adapted to different irradiance in nature was analyzed. Characteristic times of a photoinduced increase and a dark decline of ΔT in these species were 12 and 20min, respectively. The ΔT was not confirmed to be the main contributor to the observed middle phase of NPQ relaxation kinetics (τ= 10-28min). Comparison of rate of photoinduced increase in ΔT and photosystem II quantum yield recovery showed that the former did not affect the tolerance of the photosynthetic apparatus (PSA) to irradiances up to 150µmol PAR·m-2·s-1. Irradiance tolerance correlated with the rate of "apparent NPQ" induction. Considering that the induction of apparent NPQ involves processes significantly faster than ΔT, we suggest that the photoprotective mechanism induction rate is crucial for tolerance of the PSA to moderate irradiance during the initial stage of light acclimation (first several minutes upon the onset of illumination).

The Early Worm Catches the Bird? Productivity and Patterns of Trichobilharzia szidati Cercarial Emission from Lymnaea stagnalis.

Digenean trematodes are common and abundant in aquatic habitats and their free-living larvae, the cercariae, have recently been recognized as important components of ecosystems in terms of comprising a significant proportion of biomass and in having a potentially strong influence on food web dynamics. One strategy to enhance their transmission success is to produce high numbers of cercariae which are available during the activity peak of the next host. In laboratory experiments with 13 Lymnaea stagnalis snails infected with Trichobilharzia szidati the average daily emergence rate per snail was determined as 2,621 cercariae, with a maximum of 29,560. During a snail’s lifetime this summed up to a mass equivalent of or even exceeding the snail’s own body mass. Extrapolated for the eutrophic pond where the snails were collected, annual T. szidati biomass may reach 4.65 tons, a value equivalent to a large Asian elephant. Emission peaks were observed after the onset of illumination, indicating emission synchronizing with the high morning activities of the definitive hosts, ducks. However, high cercarial emission is possible throughout the day under favorable lightning conditions. Therefore, although bird schistosomes, such as T. szidati constitute only a fraction of the diverse trematode communities in the studied aquatic ecosystem, their cercariae can still pose a considerable risk for humans of getting cercarial dermatitis (swimmer's itch) due to the high number of cercariae emitted from infected snails.

Transcriptomic, proteomic and metabolic changes in Arabidopsis thaliana leaves after the onset of illumination.

BackgroundLight plays an important role in plant growth and development. In this study, the impact of light on physiology of 20-d-old Arabidopsis leaves was examined through transcriptomic, proteomic and metabolomic analysis. Since the energy-generating electron transport chains in chloroplasts and mitochondria are encoded by both nuclear and organellar genomes, sequencing total RNA after removal of ribosomal RNAs provides essential information on transcription of organellar genomes. The changes in the levels of ADP, ATP, NADP+, NADPH and 41 metabolites upon illumination were also quantified.ResultsUpon illumination, while the transcription of the genes encoded by the plastid genome did not change significantly, the transcription of nuclear genes encoding different functional complexes in the photosystem are differentially regulated whereas members of the same complex are co-regulated with each other. The abundance of mRNAs and proteins encoded by all three genomes are, however, not always positively correlated. One such example is the negative correlation between mRNA and protein abundances of the photosystem components, which reflects the importance of post-transcriptional regulation in plant physiology.ConclusionThis study provides systems-wide datasets which allow plant researchers to examine the changes in leaf transcriptomes, proteomes and key metabolites upon illumination and to determine whether there are any correlations between changes in transcript and protein abundances of a particular gene or pathway upon illumination. The integration of data of the organelles and the photosystems, Calvin-Benson cycle, carbohydrate metabolism, glycolysis, the tricarboxylic acid cycle and respiratory chain, thereby provides a more complete picture to the changes in plant physiology upon illumination than has been attained to date.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0726-3) contains supplementary material, which is available to authorized users.

Post-illumination transient O2 -uptake is driven by photorespiration in tobacco leaves.

This study aims to elucidate the molecular mechanism for the transient increase in the O2 -uptake rate in tobacco (Nicotiana tabacum cv Xanthi) leaves after turning off actinic lights (ALs). The photosynthetic O2 evolution rate reaches a maximum shortly after the onset of illumination with ALs and then decreases to zero in atmospheric CO2 /O2 conditions. After turning off the ALs, tobacco leaves show a transient increase in the O2 -uptake rate, the post-illumination transient O2 -uptake, and thereafter, the O2 -uptake rate decreases to the level of the dark-respiration rate. Photosynthetic linear electron flow, evaluated as the quantum yield of photosystem II [Y(II)], maintained a steady-state value distinct from the photosynthetic O2 -evolution rate. In high-[CO2 ] conditions, the photosynthetic O2 -evolution rate and Y(II) showed a parallel behavior, and the post-illumination transient O2 -uptake was suppressed. On the other hand, in maize leaves (a C4 plant), even in atmospheric CO2 /O2 conditions, Y(II) paralleled the photosynthetic O2 -evolution rate and the post-illumination transient O2 -uptake was suppressed. Hypothesizing that the post-illumination transient O2 -uptake is driven by C3 plant photorespiration in tobacco leaves, we calculated both the ribulose 1,5-bisphosphate carboxylase- and oxygenase-rates (Vc and Vo) from photosynthetic O2 -evolution and the post-illumination transient O2 -uptake rates. These values corresponded to those estimated from simultaneous chlorophyll fluorescence/O2 -exchange analysis. Furthermore, the H+ -consumption rate for ATP synthesis in both photosynthesis and photorespiration, calculated from both Vc and Vo that were estimated from chlorophyll fluorescence/CO2 -exchange analysis, showed a positive linear relationship with the dissipation rate of the electrochromic shift signal. Thus, these findings support our hypothesis.

Microsensor measurements of hydrogen gas dynamics in cyanobacterial microbial mats.

We used a novel amperometric microsensor for measuring hydrogen gas production and consumption at high spatio-temporal resolution in cyanobacterial biofilms and mats dominated by non-heterocystous filamentous cyanobacteria (Microcoleus chtonoplastes and Oscillatoria sp.). The new microsensor is based on the use of an organic electrolyte and a stable internal reference system and can be equipped with a chemical sulfide trap in the measuring tip; it exhibits very stable and sulfide-insensitive measuring signals and a high sensitivity (1.5–5 pA per μmol L-1 H2). Hydrogen gas measurements were done in combination with microsensor measurements of scalar irradiance, O2, pH, and H2S and showed a pronounced H2 accumulation (of up to 8–10% H2 saturation) within the upper mm of cyanobacterial mats after onset of darkness and O2 depletion. The peak concentration of H2 increased with the irradiance level prior to darkening. After an initial build-up over the first 1–2 h in darkness, H2 was depleted over several hours due to efflux to the overlaying water, and due to biogeochemical processes in the uppermost oxic layers and the anoxic layers of the mats. Depletion could be prevented by addition of molybdate pointing to sulfate reduction as a major sink for H2. Immediately after onset of illumination, a short burst of presumably photo-produced H2 due to direct biophotolysis was observed in the illuminated but anoxic mat layers. As soon as O2 from photosynthesis started to accumulate, the H2 was consumed rapidly and production ceased. Our data give detailed insights into the microscale distribution and dynamics of H2 in cyanobacterial biofilms and mats, and further support that cyanobacterial H2 production can play a significant role in fueling anaerobic processes like e.g., sulfate reduction or anoxygenic photosynthesis in microbial mats.

Carbon/nitrogen-doped TiO2: New synthesis route, characterization and application for phenol degradation

Porous nanocrystalline carbon and nitrogen (CN)-doped TiO2 photocatalyst was prepared using carbon tetrachloride and polyaniline as precursors. The obtained powders were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and gravimetric analysis. The purpose of this work was to explore the state and location of nitrogen and carbon atoms introduced inside the TiO2 lattice and to study the exploitation of the photocatalytic activity of the CN-doped TiO2 for application in phenol degradation under UV illumination. After 30min from the illumination onset, 64% and 57% of the phenol were degraded when the CN-doped TiO2 and TiO2 catalysts were used respectively.

Abstract 92: Understanding The Impact Of Anesthetics On Ischemic Cortical Damage By Inducing Stroke In Awake, Freely Moving Mice

Anesthetics such as isoflurane are commonly used to sedate experimental animals during the induction of stroke. However, there is an abundance of data showing that anesthetics modulate brain excitability, blood flow and vascular tone. Given these diverse effects, it begs the question of to what extent do anesthetics modulate ischemic damage and functional outcome? To better understand the effect of isoflurane on stroke outcome, we developed a protocol for inducing photothrombotic cerebral ischemia in an awake, unanesthetized mouse. This protocol involves temporary attachment of a 1mm diameter plastic fiber optic cable to a previously implanted Luer lock headmount for delivery of photoactivating green laser light (532nm, 1100 mW/cm 2 ) for 15 minutes to the forelimb somatosensory cortex. Evidence for compromised forelimb use is observed within 2 minutes of illumination onset. Histological assessment of ischemic damage and behavioural tests of functional outcome are being examined at different times following stroke induction in awake versus 1.5% isoflurane anesthetized mice. Our preliminary results suggest that infarct volume at 1 and 7 days post-stroke is significantly increased in awake relative to anesthetized mice ( 1 day = 3.4mm 3 ± 0.6 vs. 2.03mm 3 ±0.39; 7 days = 2.97mm 3 +/-0.36 vs. 1.97mm 3 +/-0.19, respectively). Consistent with larger infarct volume, mice that were awake during stroke induction show greater and more persistent deficits in sensory function of the affected forepaw. These experiments will enhance our understanding of whether anesthetics modulate ischemic damage. Further, our simple method for inducing stroke in awake, freely moving animals might be useful for future neuroprotective studies that wish to avoid the potentially confounding effects of anesthetics or examine state-dependent modulation of ischemic damage (e.g. sleep, exercise).