Light intensity regulation of cab gene transcription is signaled by the redox state of the plastoquinone pool.

The eukaryotic green alga Dunaliella tertiolecta acclimates to decreased growth irradiance by increasing cellular levels of light-harvesting chlorophyll protein complex apoproteins associated with photosystem II (LHCIIs), whereas increased growth irradiance elicits the opposite response. Nuclear run-on transcription assays and measurements of cab mRNA stability established that light intensity-dependent changes in LHCII are controlled at the level of transcription. cab gene transcription in high-intensity light was partially enhanced by reducing plastoquinone with 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU), whereas it was repressed in low-intensity light by partially inhibiting the oxidation of plastoquinol with 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB). Uncouplers of photosynthetic electron transport and inhibition of water splitting had no effect on LHCII levels. These results strongly implicate the redox state of the plastoquinone pool in the chloroplast as a photon-sensing system that is coupled to the light-intensity regulation of nuclear-encoded cab gene transcription. The accumulation of cellular chlorophyll at low-intensity light can be blocked with cytoplasmically directed phosphatase inhibitors, such as okadaic acid, microcystin L-R, and tautomycin. Gel mobility-shift assays revealed that cells grown in high-intensity light contained proteins that bind to the promoter region of a cab gene carrying sequences homologous to higher plant light-responsive elements. On the basis of these experimental results, we propose a model for a light intensity signaling system where cab gene expression is reversibly repressed by a phosphorylated factor coupled to the redox status of plastoquinone through a chloroplast protein kinase.

Study of interaction between Si(O,C) nanowires and the biological system

Nanomedicine is a new branch of medicine, based on the potentiality and intrinsic properties of nanomaterials. Indeed, the nanomaterials ( i.e. the materials with nano and under micron size) can be suitable to different applications in biomedicine. The nanostructures can be used by taking advantage of their properties (for example superparamagnetic nanoparticles) or functionalized to deliver the drug in a specific target, thanks the ability to cross biological barriers. The size and the shape of 1D-nanostructures (nanotubes and nanowires) have an important role on the cell fate: their morphology plays a key role on the interaction between nanostructure and the biological system. For this reason the 1D nanostructure are interesting for their ability to mime the biological system. An implantable material or device must therefore integrate with the surrounding extracellular matrix (ECM), a complex network of proteins with structural and signaling properties. Innovative techniques allow the generation of complex surface patterns that can resemble the structure of the ECM, such as 1D nanostructures. NWs based on cubic silicon carbide (3C-SiC), either bare (3C-SiC NWs) or surrounded by an amorphous shell (3C-SiC/SiO2 core/shell NWs), and silicon oxycarbide nanowires (SiOxCy NWs) can meet the chemical, mechanical and electrical requirements for tissue engineering and have a strong potential to pave the way for the development of a novel generation of implantable nano-devices. Silicon oxycarbide shows promising physical and chemical properties as elastic modulus, bending strength and hardness, chemical durability superior to conventional silicate glasses in aggressive environments and high temperature stability up to 1300 °C. Moreover, it can easily be engineered through functionalization and decoration with macro-molecules and nanoparticles. Silicon carbide has been extensively studied for applications in harsh conditions, as chemical environment, high electric field and high and low temperature, owing to its high hardness, high thermal conductivity, chemical inertness and high electron mobility. Also, its cubic polytype (3C) is highly biocompatible and hemocompatible, and some prototypes of biomedical applications and biomedical devices have been already realized starting from 3C-SiC thin films. Cubic SiC-based NWs can be used as a biomimetic biomaterial, providing a robust and novel biocompatible biological interface . We cultured in vitro A549 human lung adenocarcinoma epithelial cells and L929 murine fibroblast cells over core/shell SiC/SiO2, SiOxCy and bare 3C-SiC nanowire platforms, and analysed the cytotoxicity, by indirect and direct contact tests, the cell adhesion, and the cell proliferation. These studies showed that all the nanowires are biocompatible according to ISO 10993 standards. We evaluated the blood compatibility through the interaction of the nanowires with platelet rich plasma. The adhesion and activation of platelets on the nanowire bundles, assessed via SEM imaging and soluble P-selectin quantification, indicated that a higher platelet activation is induced by the core/shell structures compared to the bare ones. Further, platelet activation is higher with 3C-SiC/SiO2 NWs and SiOxCyNWs, which therefore appear suitable in view of possible tissue regeneration. On the contrary, bare 3C-SiC NWs show a lower platelet activation and are therefore promising in view of implantable bioelectronics devices, as cardiovascular implantable devices. The NWs properties are suitable to allow the design of a novel subretinal Micro Device (MD). This devices is based on Si NWs and PEDOT:PSS, though the well know principle of the hybrid ordered bulk heterojunction (OBHJ). The aim is to develop a device based on a well-established photovoltaic technology and to adapt this know-how to the prosthetic field. The hybrid OBHJ allows to form a radial p–n junction on a nanowire/organic structure. In addition, the nanowires increase the light absorption by means of light scattering effects: a nanowires based p-n junction increases the light absorption up to the 80%, as previously demonstrated, overcoming the Shockley-Queisser limit of 30 % of a bulk p-n junction. Another interesting employment of these NWs is to design of a SiC based epicardial-interacting patch based on teflon that include SiC nanowires. . Such contact patch can bridge the electric conduction across the cardiac infarct as nanowires can ‘sense’ the direction of the wavefront propagation on the survival cardiac tissue and transmit it to the downstream surivived regions without discontinuity. The SiC NWs are tested in terms of toxicology, biocompatibility and conductance among cardiomyocytes and myofibroblasts.

Nonclassical light revealed by the joint statistics of simultaneous measurements

Nonclassicality cannot be a single-observable property, since the statistics of any quantum observable is compatible with classical physics. We develop a general procedure to reveal nonclassical behavior of light states from the joint statistics arising in the practical measurement of multiple observables. Beside embracing previous approaches, this protocol can disclose nonclassical features for standard examples of classical-like behavior, such as SU(2) and Glauber coherent states. When combined with other criteria, this would imply that every light state is nonclassical.

The differential evolution of hot- and cold-dust in galaxies in the last 7.5 GYR

Tese de mestrado em Física, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2016

Light list, including fog signals, Atlantic and gulf coasts of the United States ...

Mode of access: Internet.

Systemic regulation of intestinal iron absorption

The intestinal absorption of the essential trace element iron and its mobilization from storage sites in the body are controlled by systemic signals that reflect tissue iron requirements. Recent advances have indicated that the liver-derived peptide hepcidin plays a central role in this process by repressing iron release from intestinal enterocytes, macrophages and other body cells. When iron requirements are increased, hepcidin levels decline and more iron enters the plasma. It has been proposed that the level of circulating diferric transferrin, which reflects tissue iron levels, acts as a signal to alter hepcidin expression. In the liver, the proteins HFE, transferrin receptor 2 and hemojuvelin may be involved in mediating this signal as disruption of each of these molecules decreases hepcidin expression. Patients carrying mutations in these molecules or in hepcidin itself develop systemic iron loading (or hemochromatosis) due to their inability to down regulate iron absorption. Hepcidin is also responsible for the decreased plasma iron or hypoferremia that accompanies inflammation and various chronic diseases as its expression is stimulated by pro-inflammatory cytokines such as interleukin 6. The mechanisms underlying the regulation of hepcidin expression and how it acts on cells to control iron release are key areas of ongoing research.

Modelling oil droplet absorption spectra and spectral sensitivities of bird cone photoreceptors

Birds have four spectrally distinct types of single cones that they use for colour vision. It is often desirable to be able to model the spectral sensitivities of the different cone types, which vary considerably between species. However, although there are several mathematical models available for describing the spectral absorption of visual pigments, there is no model describing the spectral absorption of the coloured oil droplets found in three of the four single cone types. In this paper, we describe such a model and illustrate its use in estimating the spectral sensitivities of single cones. Furthermore, we show that the spectral locations of the wavelengths of maximum absorbance (lambda(max)) of the short- (SWS), medium- (MWS) and long- (LWS) wavelength-sensitive visual pigments and the cut-off wavelengths (lambda(cut)) of their respective C-, Y- and R-type oil droplets can be predicted from the lambda(max) of the ultraviolet- (UVS)/violet- ( VS) sensitive visual pigment.

Tolerance of endolithic algae to elevated temperature and light in the coral Montipora monasteriata from the southern Great Barrier Reef

Photosynthetic endolithic algae and cyanobacteria live within the skeletons of many scleractinians. Under normal conditions, less than 5% of the photosynthetically active radiation (PAR) reaches the green endolithic algae because of the absorbance of light by the endosymbiotic dinoflagellates and the carbonate skeleton. When corals bleach (loose dinoflagellate symbionts), however, the tissue of the corals become highly transparent and photosynthetic microendoliths may be exposed to high levels of both thermal and solar stress. This study explores the consequence of these combined stresses on the phototrophic endoliths inhabiting the skeleton of Montipora monasteriata, growing at Heron Island, on the southern Great Barrier Reef. Endoliths that were exposed to sun after tissue removal were by far more susceptible to thermal photoinhibition and photo-damage than endoliths under coral tissue that contained high concentrations of brown dinoflagellate symbionts. While temperature or light alone did not result in decreased photosynthetic efficiency of the endoliths, combined thermal and solar stress caused a major decrease and delayed recovery. Endoliths protected under intact tissue recovered rapidly and photoacclimated soon after exposure to elevated sea temperatures. Endoliths under naturally occurring bleached tissue of M. monasteriata colonies (bleaching event in March 2004 at Heron Island) acclimated to increased irradiance as the brown symbionts disappeared. We suggest that two major factors determine the outcome of thermal bleaching to the endolith community. The first is the microhabitat and light levels under which a coral grows, and the second is the susceptibility of the coral-dinoflagellates symbiosis to thermal stress. More resistant corals may take longer to bleach allowing endoliths time to acclimate to a new light environment. This in turn may have implications for coral survival.

The impact of spectral composition and light periodicity on the activity of two antioxidant enzymes (SOD and CAT) in the coral Favia favus

In oligotrophic waters the light spectrum is mostly blue, and therefore the physiological and biochemical responses to blue light occurring in the coral tissue and in the symbiotic algae are important. Examination of the wavelength dependence of two free radical scavenger enzyme activity revealed an increase in activity in the blue light range (440-480 nm) compared to the red (640680 nm) in the full visible light (400-700 nm) range. These data show for the first time the relationship between the action spectra of photosynthesis and the activity of two main antioxidant enzymes in the symbiotic coral Favia favus. It was found that in the animal (host) the enzyme response to the spectral distribution of light was higher than that of the zooxanthellae, probably due to accumulation of free radicals within the host tissue. Furthermore, we found that the activity of these enzymes is affected in nature by the length of the day and night, and in the laboratory, by the duration of the illumination. Changes in the pigment concentrations were also observed in response to growth under the blue region and the whole PAR spectrum, while fluorescence measurements with the fast repetition rate fluorometer (FRRF) showed a decrease in the sigma cross section and a decrease in the quantum yield also in the blue part of the spectrum. These changes of scavenger enzymes activity, pigment concentration and fluorescence yield at different light spectra are vital in acclimatization and survival of corals in shallow water environments with high light radiation. (c) 2005 Elsevier B.V. All rights reserved.

Cone photoreceptor oil droplet pigmentation is affected by ambient light intensity

The cone photoreceptors of many vertebrates contain spherical organelles called oil droplets. In birds, turtles, lizards and some lungfish the oil droplets are heavily pigmented and function to filter the spectrum of light incident upon the visual pigment within the outer segment. Pigmented oil droplets are beneficial for colour discrimination in bright light, but at lower light levels the reduction in sensitivity caused by the pigmentation increasingly outweighs the benefits generated by spectral tuning. Consequently, it is expected that species with pigmented oil droplets should modulate the density of pigment in response to ambient light intensity and thereby regulate the amount of light transmitted to the outer segment. In this study, microspectrophotometry was used to measure the absorption spectra of cone oil droplets in chickens (Gallus gallus domesticus) reared under bright (unfiltered) or dim (filtered) sunlight. Oil droplet pigmentation was found to be dependent on the intensity of the ambient light and the duration of exposure to the different lighting treatments. In adult chickens reared in bright light, the oil droplets of all cone types (except the violet-sensitive single cones, whose oil droplet is always non-pigmented) were more densely pigmented than those in chickens reared in dim light. Calculations show that the reduced levels of oil droplet pigmentation in chickens reared in dim light would increase the sensitivity and spectral bandwidth of the outer segment significantly. The density of pigmentation in the oil droplets presumably represents a trade-off between the need for good colour discrimination and absolute sensitivity. This might also explain why nocturnal animals, or those that underwent a nocturnal phase during their evolution, have evolved oil droplets with low pigment densities or no pigmentation or have lost their oil droplets altogether.

Quantitative scattering of melanin solutions

The optical scattering coefficient of a dilute, well-solubilized eumelanin solution has been accurately measured as a function of incident wavelength, and found to contribute < 6% of the total optical attenuation between 210 and 325 nm. At longer wavelengths (325-800 nm), the scattering was less than the minimum sensitivity of our instrument. This indicates that ultraviolet and visible optical density spectra can be interpreted as true absorption with a high degree of confidence. The scattering coefficient versus wavelength was found to be consistent with Rayleigh theory for a particle radius of 38 6 1 nm. Our results shed important light on the role of melanins as photoprotectants.

Photochemical degradation of polystyrene

In this work the oxidative degradation of pure polystyrene, polybutadiene and butadiene-modified polystyrene (normally called high impact polystyrene or HIPS) have been studied using a variety of physical and chemical techniques. The changes in dynamic-mechanical properties occurring during the ultra-violet light accelerated weathering of these polymers were followed by a visco-elastometric technique (Rheovibron) in the solid phase over a wide temperature range. Selective cross-linking of the polybutadiene in high-impact polystyrene caused the depression of the low temperature damping peak (tan d) with a corresponding sharp peak in tan d at ambient temperature accompanied by an integral rise in complex modulus. During the same period of photoxidation, the hydroperoxide concentration and gel content increased rapidly, reaching a maximum before decomposing photolytically with the destruction of unsaturation and with the formation of stable oxidation products. Infra-red spectroscopy showed the formation of carbonyl and hydroxyl groups. a,ß-unsaturated carbonyl was also identified and was formed by decomposition of both allylic hydroperoxide and initial peroxidic gel by ß-scission of the graft between polybutadiene and polystyrene. With further photoxidation a more stable ether gel was formed involving the destruction of the conjugating double bond of a,ß-unsaturated carbonyl. Addition of saturated and unsaturated ketones which are potential sensitisers of photoxidation to high-impact polystyrene and polybutadiene failed to photo-initiate the oxygen absorption of the polymers. A prior thermal oxidative treatment on the other hand eliminated the auto- accelerating stage leading to linear kinetics as the concentration of thermally-produced hydroperoxide approached a maximum. Antioxidants which act by destroying hydroperoxide lengthened the induction period to rapid oxygen absorption, whilst a phenolic antioxidant behaved as a weak photo-activator initially and a retarder later. Prior photolysis of high-impact polystyrene photo-activated the unsaturated component and caused similar changes in dynamic-mechanical properties to those found during photoxidation although at a much lower rate. Polybutadiene behaves as a photo-pro-oxidant for the destruction of polystyrene in high-impact polystyrene.

Methodology for development of a physiological model incorporating CYP3A and P-glycoprotein for the prediction of intestinal drug absorption

The small intestine poses a major barrier to the efficient absorption of orally administered therapeutics. Intestinal epithelial cells are an extremely important site for extrahepatic clearance, primarily due to prominent P-glycoprotein-mediated active efflux and the presence of cytochrome P450s. We describe a physiologically based pharmacokinetic model which incorporates geometric variations, pH alterations and descriptions of the abundance and distribution of cytochrome 3A and P-glycoprotein along the length of the small intestine. Simulations using preclinical in vitro data for model drugs were performed to establish the influence of P-glycoprotein efflux, cytochrome 3A metabolism and passive permeability on drug available for absorption within the enterocytes. The fraction of drug escaping the enterocyte (F(G)) for 10 cytochrome 3A substrates with a range of intrinsic metabolic clearances were simulated. Following incorporation of P-glycoprotein in vitro efflux ratios all predicted F(G) values were within 20% of observed in vivo F(G). The presence of P-glycoprotein increased the level of cytochrome 3A drug metabolism by up to 12-fold in the distal intestine. F(G) was highly sensitive to changes in intrinsic metabolic clearance but less sensitive to changes in intestinal drug permeability. The model will be valuable for quantifying aspects of intestinal drug absorption and distribution.

An investigation into the wavelength stability of polymer optical fibre Bragg gratings

The inscription of Bragg gratings has been demonstrated in PMMA-based polymer optical fibre. The water affinity of PMMA can introduce significant wavelength change in a polymer optical fibre Bragg grating (POFBG). In polymer optical fibre losses are much higher than with silica fibre. Very strong absorption bands related to higher harmonics of vibrations of the C-H bond dominate throughout the visible and near infrared. Molecular vibration in substances generates heat, which is referred to as the thermal effect of molecular vibration. This means that a large part of the absorption of optical energy in those spectral bands will convert into thermal energy, which eventually drives water content out of the polymer fibre and reduces the wavelength of POFBG. In this work we have investigated the wavelength stability of POFBGs in different circumstances. The experiment has shown that the characteristic wavelength of a POFBG starts decreasing after a light source is applied to it. This decrease continues until equilibrium inside the fibre is established, depending on the initial water content inside the fibre, the surrounding humidity, the optical power applied, and the fibre size. Our investigation has shown that POFBGs operating at around 850 nm show much smaller wavelength reduction than those operating at around 1550 nm in the same fibre; POFBGs with different diameters show different changes; POFBGs powered by a low level light source, or operating in a very dry environment are least affected by this thermal effect.

3D culture of bone-derived cells immobilised in alginate following light-triggered gelation

Photoreactive liposomes have been exploited as a means of developing 3D tissue constructs. Liposomes formulated using the photosensitive lipid 1,2-bis(4-(n-butyl)phenylazo-4′-phenylbutyroyl)phosphatidylcholine (Bis Azo PC), which undergoes conformational change on stimulation with long wavelength ultraviolet light, were prepared with entrapped CaCl2 before being incorporated into a 4% alginate solution. It was shown that stimulation of the photosensitive lipid using a light emitting diode (LED) (peak emission at 385 nm, dose equivalent to 9 mJ/cm2) caused the release of liposome-entrapped CaCl2, resulting in cross-linking of the alginate solution and immobilisation of bone-derived cells over a range of seeding densities, approximately 97% of which remained viable for periods of up to 14 days in culture. Entrapment volumes of a variety of liposome types were evaluated and interdigitating fusion vesicles were identified as having the highest payload (24%), however the inclusion of cholesterol as a means of shifting Bis Azo PC sensitivity into the visible light wavelengths resulted in an approximately 10-fold reduction in calcium entrapment. This application of light-sensitised liposomes offers the potential to create complex tissue engineering substrates containing cells immobilised in precise locations, in contrast with substrates onto which cells are seeded post-production. © 2007 Elsevier B.V. All rights reserved.