Visual field losses in workers exposed to mercury vapor

Visual field losses associated with mercury (Hg) exposure have only been assessed in patients exposed to methylmercury. Here we evaluate the automated visual field in 35 ex-workers (30 males; 44.20+/-5.92 years) occupationaly exposed to mercury vapor and 34 controls (21 males; 43.29+/-8.33 years). Visual fields were analyzed with the Humphrey Field Analyzer II (model 750i) using two tests: the standard automated perimetry (SAP, white-on-white) and the short wavelength automated perimetry (SWAP, blue-on-yellow) at 76 locations within a 27 degrees central visual field. Results were analyzed as the mean of the sensitivities measured at the fovea, and at five successive concentric rings, of increasing eccentricity, within the central field. Compared to controls, visual field sensitivities of the experimental group measured using SAP were lower for the fovea as well as for all five eccentricity rings (p<0.05). Sensitivities were significantly lower in the SWAP test (p<0.05) for four of the five extra-foveal eccentricity rings; they were not significant for the fovea (p = 0.584) or for the 15 degrees eccentricity ring (p = 0.965). These results suggest a widespread reduction of sensitivity in both visual field tests. Previous reports in the literature describe moderate to severe concentric constriction of the visual field in subjects with methylmercury intoxication measured manually with the Goldman perimeter. The present results amplify concerns regarding potential medical risks of exposure to environmental mercury sources by demonstrating significant and widespread reductions of visual sensitivity using the more reliable automated perimetry. (C) 2007 Elsevier Inc. All rights reserved.

Atividade da catalase e da lactato desidrogenase em tilápias submetidas a estresse de confinamento: efeito da cor do ambiente

Avaliaram-se os efeitos da cor do ambiente sobre o crescimento e a atividade da enzima antioxidante catalase (CAT) e da lactato desidrogenase (LDH) em tilápias do Nilo (n=24; 36,2±3,6g). Oito exemplares foram mortos para determinação da atividade basal das enzimas e os demais permaneceram isolados durante 14 dias sob espectro de luz branca ou azul (n=8 peixes/tratamento). A seguir os peixes foram submetidos a um estresse diário de confinamento de 90 minutos (15° ao 28° dia) e pesados semanalmente para cálculo da taxa de crescimento específico (TCE). A TCE negativa confirmou que o confinamento provocou estresse nos peixes, independentemente da cor do ambiente. O aumento da atividade da LDH no músculo vermelho dos peixes mantidos sob luz branca ou azul indicou mudança do metabolismo aeróbio para anaeróbio. O estresse reduziu a atividade da CAT no músculo branco dos peixes mantidos sob a luz branca ou azul. Na musculatura vermelha, esta redução ocorreu apenas nos animais mantidos sob a luz branca. O confinamento aumenta os processos metabólicos anaeróbios e é adequado para estudos sobre os efeitos do estresse. O espectro de luz azul não evita a redução do crescimento e a demanda energética anaeróbia em situações de estresse, mas preserva a atividade da CAT, contribuindo para o bem-estar da tilápia.

Broad combined orange-red emissions from Eu2+- and Eu3+-doped low-silica calcium aluminosilicate glass

In this paper, a broad combined orange-red emission from Eu2+- and Eu3+-doped low-silica calcium aluminosilicate (LSCAS) glass is reported. Spectroscopic results demonstrate that it is possible to tune the emission wavelength by changing the excitation wavelength in the UV-Vis region. The color coordinates for the emission spectra were calculated, and using the Commission Internationale de l'Eclairage 1931 and 1976 chromatic diagrams, it is possible to note that they are dependent on the excitation wavelength. In addition, the (u', v') color coordinates for the investigated LSCAS samples are close to the Planckian spectrum in the cold region between 2000 and 2600K. Our results show that the Eu:LSCAS system can be used in a white light phosphor when mixed in aggregate with phosphors using green-yellow luminescent ions. (c) 2012 Optical Society of America

Morphological evidence of neurotoxicity in retina after methylmercury exposure

The visual system is particularly sensitive to methylmercury (MeHg) exposure and, therefore, provides a useful model for investigating the fundamental mechanisms that direct toxic effects. During a period of 70 days, adult of a freshwater fish species Hoplias malabaricus were fed with fish prey previously labeled with two different doses of methylmercury (0.075 and 0.75 mu g g(-1)) to determine the mercury distribution and morphological changes in the retina. Mercury deposits were found in the photoreceptor layer, in the inner plexiform layer and in the outer plexiform layer, demonstrating a dose-dependent bioaccumulation. The ultrastructure analysis of retina revealed a cellular deterioration in the photoreceptor layer, morphological changes in the inner and outer segments of rods, structural changes in the plasma membrane of rods and double cones, changes in the process of removal of membranous discs and a structural discontinuity. These results lead to the conclusion that methylmercury is able to cross the blood-retina barrier, accumulate in the cells and layers of retina and induce changes in photoreceptors of H. malabaricus even under subchronic exposure. (c) 2012 Elsevier Inc. All rights reserved.

Portable light transmission measuring system for preserved corneas

Abstract Background The authors have developed a small portable device for the objective measurement of the transparency of corneas stored in preservative medium, for use by eye banks in evaluation prior to transplantation. Methods The optical system consists of a white light, lenses, and pinholes that collimate the white light beams and illuminate the cornea in its preservative medium, and an optical filter (400–700 nm) that selects the range of the wavelength of interest. A sensor detects the light that passes through the cornea, and the average corneal transparency is displayed. In order to obtain only the tissue transparency, an electronic circuit was built to detect a baseline input of the preservative medium prior to the measurement of corneal transparency. The operation of the system involves three steps: adjusting the "0 %" transmittance of the instrument, determining the "100 %" transmittance of the system, and finally measuring the transparency of the preserved cornea inside the storage medium. Results Fifty selected corneas were evaluated. Each cornea was submitted to three evaluation methods: subjective classification of transparency through a slit lamp, quantification of the transmittance of light using a corneal spectrophotometer previously developed, and measurement of transparency with the portable device. Conclusion By comparing the three methods and using the expertise of eye bank trained personnel, a table for quantifying corneal transparency with the new device has been developed. The correlation factor between the corneal spectrophotometer and the new device is 0,99813, leading to a system that is able to standardize transparency measurements of preserved corneas, which is currently done subjectively.

Light energy management in peach: utilization, photoprotection , photodamage and recovery. Maximizing light absorption in orchard is not always the best solution

The relation between the intercepted light and orchard productivity was considered linear, although this dependence seems to be more subordinate to planting system rather than light intensity. At whole plant level not always the increase of irradiance determines productivity improvement. One of the reasons can be the plant intrinsic un-efficiency in using energy. Generally in full light only the 5 – 10% of the total incoming energy is allocated to net photosynthesis. Therefore preserving or improving this efficiency becomes pivotal for scientist and fruit growers. Even tough a conspicuous energy amount is reflected or transmitted, plants can not avoid to absorb photons in excess. The chlorophyll over-excitation promotes the reactive species production increasing the photoinhibition risks. The dangerous consequences of photoinhibition forced plants to evolve a complex and multilevel machine able to dissipate the energy excess quenching heat (Non Photochemical Quenching), moving electrons (water-water cycle , cyclic transport around PSI, glutathione-ascorbate cycle and photorespiration) and scavenging the generated reactive species. The price plants must pay for this equipment is the use of CO2 and reducing power with a consequent decrease of the photosynthetic efficiency, both because some photons are not used for carboxylation and an effective CO2 and reducing power loss occurs. Net photosynthesis increases with light until the saturation point, additional PPFD doesn’t improve carboxylation but it rises the efficiency of the alternative pathways in energy dissipation but also ROS production and photoinhibition risks. The wide photo-protective apparatus, although is not able to cope with the excessive incoming energy, therefore photodamage occurs. Each event increasing the photon pressure and/or decreasing the efficiency of the described photo-protective mechanisms (i.e. thermal stress, water and nutritional deficiency) can emphasize the photoinhibition. Likely in nature a small amount of not damaged photosystems is found because of the effective, efficient and energy consuming recovery system. Since the damaged PSII is quickly repaired with energy expense, it would be interesting to investigate how much PSII recovery costs to plant productivity. This PhD. dissertation purposes to improve the knowledge about the several strategies accomplished for managing the incoming energy and the light excess implication on photo-damage in peach. The thesis is organized in three scientific units. In the first section a new rapid, non-intrusive, whole tissue and universal technique for functional PSII determination was implemented and validated on different kinds of plants as C3 and C4 species, woody and herbaceous plants, wild type and Chlorophyll b-less mutant and monocot and dicot plants. In the second unit, using a “singular” experimental orchard named “Asymmetric orchard”, the relation between light environment and photosynthetic performance, water use and photoinhibition was investigated in peach at whole plant level, furthermore the effect of photon pressure variation on energy management was considered on single leaf. In the third section the quenching analysis method suggested by Kornyeyev and Hendrickson (2007) was validate on peach. Afterwards it was applied in the field where the influence of moderate light and water reduction on peach photosynthetic performances, water requirements, energy management and photoinhibition was studied. Using solar energy as fuel for life plant is intrinsically suicidal since the high constant photodamage risk. This dissertation would try to highlight the complex relation existing between plant, in particular peach, and light analysing the principal strategies plants developed to manage the incoming light for deriving the maximal benefits as possible minimizing the risks. In the first instance the new method proposed for functional PSII determination based on P700 redox kinetics seems to be a valid, non intrusive, universal and field-applicable technique, even because it is able to measure in deep the whole leaf tissue rather than the first leaf layers as fluorescence. Fluorescence Fv/Fm parameter gives a good estimate of functional PSII but only when data obtained by ad-axial and ab-axial leaf surface are averaged. In addition to this method the energy quenching analysis proposed by Kornyeyev and Hendrickson (2007), combined with the photosynthesis model proposed by von Caemmerer (2000) is a forceful tool to analyse and study, even in the field, the relation between plant and environmental factors such as water, temperature but first of all light. “Asymmetric” training system is a good way to study light energy, photosynthetic performance and water use relations in the field. At whole plant level net carboxylation increases with PPFD reaching a saturating point. Light excess rather than improve photosynthesis may emphasize water and thermal stress leading to stomatal limitation. Furthermore too much light does not promote net carboxylation improvement but PSII damage, in fact in the most light exposed plants about 50-60% of the total PSII is inactivated. At single leaf level, net carboxylation increases till saturation point (1000 – 1200 μmolm-2s-1) and light excess is dissipated by non photochemical quenching and non net carboxylative transports. The latter follows a quite similar pattern of Pn/PPFD curve reaching the saturation point at almost the same photon flux density. At middle-low irradiance NPQ seems to be lumen pH limited because the incoming photon pressure is not enough to generate the optimum lumen pH for violaxanthin de-epoxidase (VDE) full activation. Peach leaves try to cope with the light excess increasing the non net carboxylative transports. While PPFD rises the xanthophyll cycle is more and more activated and the rate of non net carboxylative transports is reduced. Some of these alternative transports, such as the water-water cycle, the cyclic transport around the PSI and the glutathione-ascorbate cycle are able to generate additional H+ in lumen in order to support the VDE activation when light can be limiting. Moreover the alternative transports seems to be involved as an important dissipative way when high temperature and sub-optimal conductance emphasize the photoinhibition risks. In peach, a moderate water and light reduction does not determine net carboxylation decrease but, diminishing the incoming light and the environmental evapo-transpiration request, stomatal conductance decreases, improving water use efficiency. Therefore lowering light intensity till not limiting levels, water could be saved not compromising net photosynthesis. The quenching analysis is able to partition absorbed energy in the several utilization, photoprotection and photo-oxidation pathways. When recovery is permitted only few PSII remained un-repaired, although more net PSII damage is recorded in plants placed in full light. Even in this experiment, in over saturating light the main dissipation pathway is the non photochemical quenching; at middle-low irradiance it seems to be pH limited and other transports, such as photorespiration and alternative transports, are used to support photoprotection and to contribute for creating the optimal trans-thylakoidal ΔpH for violaxanthin de-epoxidase. These alternative pathways become the main quenching mechanisms at very low light environment. Another aspect pointed out by this study is the role of NPQ as dissipative pathway when conductance becomes severely limiting. The evidence that in nature a small amount of damaged PSII is seen indicates the presence of an effective and efficient recovery mechanism that masks the real photodamage occurring during the day. At single leaf level, when repair is not allowed leaves in full light are two fold more photoinhibited than the shaded ones. Therefore light in excess of the photosynthetic optima does not promote net carboxylation but increases water loss and PSII damage. The more is photoinhibition the more must be the photosystems to be repaired and consequently the energy and dry matter to allocate in this essential activity. Since above the saturation point net photosynthesis is constant while photoinhibition increases it would be interesting to investigate how photodamage costs in terms of tree productivity. An other aspect of pivotal importance to be further widened is the combined influence of light and other environmental parameters, like water status, temperature and nutrition on peach light, water and phtosyntate management.

Allelic Heterogeneity at the Equine KIT Locus in Dominant White (W) Horses

White coat color has been a highly valued trait in horses for at least 2,000 years. Dominant white (W) is one of several known depigmentation phenotypes in horses. It shows considerable phenotypic variation, ranging from approximately 50% depigmented areas up to a completely white coat. In the horse, the four depigmentation phenotypes roan, sabino, tobiano, and dominant white were independently mapped to a chromosomal region on ECA 3 harboring the KIT gene. KIT plays an important role in melanoblast survival during embryonic development. We determined the sequence and genomic organization of the approximately 82 kb equine KIT gene. A mutation analysis of all 21 KIT exons in white Franches-Montagnes Horses revealed a nonsense mutation in exon 15 (c.2151C>G, p.Y717X). We analyzed the KIT exons in horses characterized as dominant white from other populations and found three additional candidate causative mutations. Three almost completely white Arabians carried a different nonsense mutation in exon 4 (c.706A>T, p.K236X). Six Camarillo White Horses had a missense mutation in exon 12 (c.1805C>T, p.A602V), and five white Thoroughbreds had yet another missense mutation in exon 13 (c.1960G>A, p.G654R). Our results indicate that the dominant white color in Franches-Montagnes Horses is caused by a nonsense mutation in the KIT gene and that multiple independent mutations within this gene appear to be responsible for dominant white in several other modern horse populations.

A genetically explicit model of speciation by sensory drive within a continuous population in aquatic environments

BACKGROUND: The sensory drive hypothesis predicts that divergent sensory adaptation in different habitats may lead to premating isolation upon secondary contact of populations. Speciation by sensory drive has traditionally been treated as a special case of speciation as a byproduct of adaptation to divergent environments in geographically isolated populations. However, if habitats are heterogeneous, local adaptation in the sensory systems may cause the emergence of reproductively isolated species from a single unstructured population. In polychromatic fishes, visual sensitivity might become adapted to local ambient light regimes and the sensitivity might influence female preferences for male nuptial color. In this paper, we investigate the possibility of speciation by sensory drive as a byproduct of divergent visual adaptation within a single initially unstructured population. We use models based on explicit genetic mechanisms for color vision and nuptial coloration. RESULTS: We show that in simulations in which the adaptive evolution of visual pigments and color perception are explicitly modeled, sensory drive can promote speciation along a short selection gradient within a continuous habitat and population. We assumed that color perception evolves to adapt to the modal light environment that individuals experience and that females prefer to mate with males whose nuptial color they are most sensitive to. In our simulations color perception depends on the absorption spectra of an individual's visual pigments. Speciation occurred most frequently when the steepness of the environmental light gradient was intermediate and dispersal distance of offspring was relatively small. In addition, our results predict that mutations that cause large shifts in the wavelength of peak absorption promote speciation, whereas we did not observe speciation when peak absorption evolved by stepwise mutations with small effect. CONCLUSION: The results suggest that speciation can occur where environmental gradients create divergent selection on sensory modalities that are used in mate choice. Evidence for such gradients exists from several animal groups, and from freshwater and marine fishes in particular. The probability of speciation in a continuous population under such conditions may then critically depend on the genetic architecture of perceptual adaptation and female mate choice.

Protein-protein interaction between phototaxis receptor sensory Rhodopsin I and its transducer HtrI

The molecular complex containing the seven transmembrane helix photoreceptor S&barbelow;ensory R&barbelow;hodopsin I&barbelow; (SRI) and transducer protein HtrI (H&barbelow;alobacterial Transducer for SRI&barbelow;) mediates color-sensitive phototaxis responses in the archaeon Halobacterium salinarum. Orange light causes an attractant response by a one-photon reaction and white light (orange + UV light) a repellent response by a two-photon reaction. Three aspects of SRI-HtrI structure/function and the signal transduction pathway were explored. First, the coupling of HtrI to the photoactive site of SRI was analyzed by mutagenesis and kinetic spectroscopy. Second, SRI-HtrI mutations and suppressors were selected and characterized to elucidate the color-sensing mechanism. Third, the signal relay through the transducer-bound histidine kinase was analyzed using an in vitro reconstitution system with known and newly identified taxis components. ^ Twenty-one mutations on HtrI were introduced by site-directed mutagenesis. Several replacements of charged residues perturbed the photochemical kinetics of SRI which led to the finding of a cluster of residues at the membrane/cytoplasm interface in HtrI electrostatically coupled to the photoactive site of SRI. We found by laser-flash kinetic spectroscopy that the transducer and these residues have specific effects on the light-induced proton transfer between the retinal chromophore and the protein. ^ One of the mutations showed an unusual mutant phenotype we called “inverted” signaling, in which the cell produces a repellent response to normally attractant light. Therefore, this mutant (E56Q of HtrI) had lost the color-discrimination by the SRI-HtrI complex. We used suppressor analysis to better understand the phenotype. Certain suppressors resulted in return of attractant responses to orange light but with inversion of the normally repellent response to white light to an attractant response. To explain this and other results, we formulated the Conformational Shuttling model in which the HtrI-SRI complex is poised in a metastable equilibrium of two conformations shifted in opposite directions by orange and white light. We tested this model by behavioral analysis (computerized cell tracking and motion study) of double mutants of inverting and suppressing mutations and the results confirmed the equilibrium-shift explanation. ^ We developed an in vitro system for measuring the effect of purified transducer on the histidine-kinase CheAH that controls the flagellar motor switch. The rate of kinase autophosphorylation was stimulated >2 fold in the reconstitution of the complete signal transduction system from purified components from H. salinarum. The in vitro assay also showed that the kinase activity was reduced in the absence and in the presence of high levels of linker protein CheWH. (Abstract shortened by UMI.) ^

Signal relay between two integral membrane proteins: The sensory rhodopsin I/HtrI transducer molecular complex

The molecular complex of sensory rhodopsin I (SRI) and its transducer HtrI mediate color-sensitive phototaxis in the archaeon Halobacterium salinarum. Orange light causes an attractant response by a one-photon reaction and white light causes a repellent response by a two-photon reaction. Three aspects of this molecular complex were explored: (i) We determined the stoichiometry of SRI and HtrI to be 2:2 by gene fusion analysis. A SRI-HtrI fusion protein was expressed in H. salinarum and shown to mediate 1-photon and 2-photon phototaxis responses comparable to wild-type complex. Disulfide crosslinking demonstrated that the fusion protein is a homodimer in the membrane. Measurement of photochemical reaction kinetics and pH titration of absorption spectra established that both SRI domains are complexed to HtrI in the fusion protein, and therefore the stoichiometry is 2:2. (ii) Cytoplasmic channel closure of SRI by HtrI, an important aspect of their interaction, was investigated by incremental HtrI truncation. We found that binding of the membrane-embedded portion of HtrI is insufficient for channel closure, whereas cytoplasmic extension of the second HtrI transmembrane helix by 13 residues blocks proton conduction through the channel as well as full-length HtrI. The closure activity is localized to 5 specific residues, each of which incrementally contributes to reduction of proton conductivity. Moreover, these same residues in the dark incrementally and proportionally increase the pKa of the Asp76 counterion to the protonated Schiff base chromophore. We conclude that this critical region of HtrI alters the dark conformation of SRI as well as light-induced channel opening. (iii) We developed a procedure for reconstituting HtrI-free SRI and the SRI/HtrI complex into liposomes, which exhibit photocycles with opened and closed cytoplasmic channels, respectively, as in the membrane. This opens the way for study of the light-induced conformational change and the interaction in vitro by fluorescence and spin-labeling. Single-cysteine mutations were introduced into helix F of SRI, labeled with a nitroxide spin probe and a fluorescence probe, reconstituted into proteoliposomes, and light-induced conformational changes detected in the complex. The probe signals can now be used as the readout of signaling to analyze mutants and the kinetics of signal relay. ^

Identification and evaluation of candidate genes for inherited retinal -degenerative diseases

Although more than 100 genes associated with inherited retinal disease have been mapped to chromosomal locations, less than half of these genes have been cloned. This text includes identification and evaluation of candidate genes for three autosomal dominant forms of inherited retinal degeneration: atypical vitelliform macular dystrophy (VMD1), cone-rod dystrophy (CORD), and retinitis pigmentosa (RP). ^ VMD1 is a disorder characterized by complete penetrance but extremely variable expressivity, and includes macular or peripheral retinal lesions and peripappilary abnormalitites. In 1984, linkage was reported between VMD1 and soluble glutamate-pyruvate transaminase GPT); however, placement of GPT to 8q24 on linkage maps had been debated, and VMD1 did not show linkage to microsatellite markers in that region. This study excluded linkage between the loci by cloning GPT, identifying the nucleotide substitution associated with the GPT sozymes, and by assaying VMD1 family samples with an RFLP designed to detect the substitution. In addition, linkage of VMD1 to the known dominant macular degeneration loci was excluded. ^ CORD is characterized by early onset of color-vision deficiency, and decreased visual acuity, However, this retinal degeneration progresses to no light perception, severe macular lesion, and “bone-spicule” accumulations in the peripheral retina. In this study, the disorder in a large Texan family was mapped to the CORD2 locus of 19q13, and a mutation in the retina/pineal-specific cone-rod homeobox gene (CRX) was identified as the disease cause. In addition, mutations in CRX were associated with significantly different retinal disease phenotypes, including retinitis pigmentosa and Leber congenital amaurosis. ^ Many of the mutations leading to inherited retinal disorders have been identified in genes like CRX, which are expressed predominantly in the retina and pineal gland. Therefore, a combination of database analysis and laboratory investigation was used to identify 26 novel retina/pineal-specific expressed sequence tag (EST) clusters as candidate genes for inherited retinal disorders. Eight of these genes were mapped into the candidate regions of inherited retinal degeneration loci. ^ Two of the eight clusters mapped into the retinitis pigmentosa RP13 candidate region of 17p13, and were both determined to represent a single gene that is highly expressed in photoreceptors. This gene, the Ah receptor-interacting like protein-1 (AIPL1), was cloned, characterized, and screened for mutations in RP13 patient DNA samples. ^

In vitro reconstitution of light-harvesting POR-protochlorophyllide complex with protochlorophyllides a and b

NADPH:protochlorophyllide oxidoreductase (POR; EC1.1.33.1) is a key enzyme for the light-induced greening of angiosperms. In barley, two POR proteins exist, termed PORA and PORB. These have previously been proposed to form higher molecular weight light-harvesting complexes in the prolamellar body of etioplasts (Reinbothe, C., Lebedev, N., and Reinbothe, S. (1999)Nature 397, 80–84). Here we report the in vitro reconstitution of such complexes from chemically synthesized protochlorophyllides (Pchlides) a andb and galacto- and sulfolipids. Low temperature (77 K) fluorescence measurements revealed that the reconstituted, lipid-containing complex displayed the same characteristics of photoactive Pchlide 650/657 as the presumed native complex in the prolamellar body. Moreover, Pchlide F650/657 was converted to chlorophyllide (Chlide) 684/690 upon illumination of the reconstituted complex with a 1-ms flash of white light. Identification and quantification of acetone-extractable pigments revealed that only the PORB-bound Pchlide a had been photoactive and was converted to Chlide a, whereas Pchlide b bound to the PORA remained photoinactive. Nondenaturing PAGE of the reconstituted Pchlide a/b-containing complex further demonstrated a size similar to that of the presumed native complexin vivo, suggesting that both complexes may be identical.

LHPP, the light-harvesting NADPH:protochlorophyllide (Pchlide) oxido¬reductase:Pchlide complex of etiolated plants, is developmentally expressed across the barley leaf gradient

NADPH:protochlorophyllide oxidoreductase is a key enzyme for the light-induced greening of etiolated angiosperm plants. In barley, two POR proteins exist termed PORA and PORB that have previously been proposed to structurally and functionally cooperate in terms of a higher molecular mass light-harvesting complex named LHPP, in the prolamellar body of etioplasts [Nature 397 (1999) 80]. In this study we examined the expression pattern of LHPP during seedling etiolation and de-etiolation under different experimental conditions. Our results show that LHPP is developmentally expressed across the barley leaf gradient. We further provide evidence that LHPP operates both in plants that etiolate completely before being exposed to white light and in plants that etiolate only partially and begin light-harvesting as soon as traces of light become available in the uppermost parts of the soil. As a result of light absorption, in either case LHPP converts Pchlide a to chlorophyllide (Chlide) a and in turn disintegrates. The released Chlide a, as well as Chlide b produced upon LHPP’s light-dependent dissociation, which leads to the activation of the PORA as a Pchlide b-reducing enzyme, then bind to homologs of water-soluble chlorophyll proteins of Brassicaceae. We propose that these proteins transfer Chlide a and Chlide b to the thylakoids, where their esterification with phytol and assembly into the photosynthetic membrane complexes ultimately takes place. Presumably due to the tight coupling of LHPP synthesis and degradation, as well as WSCP formation and photosynthetic membrane assembly, efficient photo-protection is conferred onto the plant.

Self assembled and ordered group III nitride nanocolumnar structures for light emitting applications

El objetivo de este trabajo es un estudio profundo del crecimiento selectivo de nanoestructuras de InGaN por epitaxia de haces moleculares asistido por plasma, concentrandose en el potencial de estas estructuras como bloques constituyentes en LEDs de nueva generación. Varias aproximaciones al problema son discutidas; desde estructuras axiales InGaN/GaN, a estructuras core-shell, o nanoestructuras crecidas en sustratos con orientaciones menos convencionales (semi polar y no polar). La primera sección revisa los aspectos básicos del crecimiento auto-ensamblado de nanocolumnas de GaN en sustratos de Si(111). Su morfología y propiedades ópticas son comparadas con las de capas compactas de GaN sobre Si(111). En el caso de las columnas auto-ensambladas de InGaN sobre Si(111), se presentan resultados sobre el efecto de la temperatura de crecimiento en la incorporación de In. Por último, se discute la inclusión de nanodiscos de InGaN en las nanocolumnas de GaN. La segunda sección revisa los mecanismos básicos del crecimiento ordenado de nanoestructuras basadas en GaN, sobre templates de GaN/zafiro. Aumentando la relación III/V localmente, se observan cambios morfológicos; desde islas piramidales, a nanocolumnas de GaN terminadas en planos semipolares, y finalmente, a nanocolumnas finalizadas en planos c polares. Al crecer nanodiscos de InGaN insertados en las nanocolumnas de GaN, las diferentes morfologias mencionadas dan lugar a diferentes propiedades ópticas de los nanodiscos, debido al diferente carácter (semi polar o polar) de los planos cristalinos involucrados. La tercera sección recoge experimentos acerca de los efectos que la temperatura de crecimiento y la razón In/Ga tienen en la morfología y emisión de nanocolumnas ordenadas de InGaN crecidas sobre templates GaN/zafiro. En el rango de temperaturas entre 650 y 750 C, la incorporacion de In puede modificarse bien por la temperatura de crecimiento, o por la razón In/Ga. Controlar estos factores permite la optimización de la longitud de onda de emisión de las nanocolumnas de InGaN. En el caso particular de la generación de luz blanca, se han seguidos dos aproximaciones. En la primera, se obtiene emisión amarilla-blanca a temperatura ambiente de nanoestructuras donde la región de InGaN consiste en un gradiente de composiciones de In, que se ha obtenido a partir de un gradiente de temperatura durante el crecimiento. En la segunda, el apilamiento de segmentos emitiendo en azul, verde y rojo, consiguiendo la integración monolítica de estas estructuras en cada una de las nanocolumnas individuales, da lugar a emisores ordenados con un amplio espectro de emisión. En esta última aproximación, la forma espectral puede controlarse con la longitud (duración del crecimiento) de cada uno de los segmentos de InGaN. Más adelante, se presenta el crecimiento ordenado, por epitaxia de haces moleculares, de arrays de nanocolumnas que son diodos InGaN/GaN cada una de ellas, emitiendo en azul (441 nm), verde (502 nm) y amarillo (568 nm). La zona activa del dispositivo consiste en una sección de InGaN, de composición constante nominalmente y longitud entre 250 y 500 nm, y libre de defectos extendidos en contraste con capas compactas de InGaN de similares composiciones y espesores. Los espectros de electroluminiscencia muestran un muy pequeño desplazamiento al azul al aumentar la corriente inyectada (desplazamiento casi inexistente en el caso del dispositivo amarillo), y emisiones ligeramente más anchas que en el caso del estado del arte en pozos cuánticos de InGaN. A continuación, se presenta y discute el crecimiento ordenado de nanocolumnas de In(Ga)N/GaN en sustratos de Si(111). Nanocolumnas ordenadas emitiendo desde el ultravioleta (3.2 eV) al infrarrojo (0.78 eV) se crecieron sobre sustratos de Si(111) utilizando una capa compacta (“buffer”) de GaN. La morfología y eficiencia de emisión de las nanocolumnas emitiendo en el rango espectral verde pueden ser mejoradas ajustando las relaciones In/Ga y III/N, y una eficiencia cuántica interna del 30% se deriva de las medidas de fotoluminiscencia en nanocolumnas optimizadas. En la siguiente sección de este trabajo se presenta en detalle el mecanismo tras el crecimiento ordenado de nanocolumnas de InGaN/GaN emitiendo en el verde, y sus propiedades ópticas. Nanocolumnas de InGaN/GaN con secciones largas de InGaN (330-830 nm) se crecieron tanto en sustratos GaN/zafiro como GaN/Si(111). Se encuentra que la morfología y la distribución espacial del In dentro de las nanocolumnas dependen de las relaciones III/N e In/Ga locales en el frente de crecimiento de las nanocolumnas. La dispersión en el contenido de In entre diferentes nanocolumnas dentro de la misma muestra es despreciable, como indica las casi identicas formas espectrales de la catodoluminiscencia de una sola nanocolumna y del conjunto de ellas. Para las nanocolumnas de InGaN/GaN crecidas sobre GaN/Si(111) y emitiendo en el rango espectral verde, la eficiencia cuántica interna aumenta hasta el 30% al disminuir la temperatura de crecimiento y aumentar el nitrógeno activo. Este comportamiento se debe probablemente a la formación de estados altamente localizados, como indica la particular evolución de la energía de fotoluminiscencia con la temperatura (ausencia de “s-shape”) en muestras con una alta eficiencia cuántica interna. Por otro lado, no se ha encontrado la misma dependencia entre condiciones de crecimiento y efiencia cuántica interna en las nanoestructuras InGaN/GaN crecidas en GaN/zafiro, donde la máxima eficiencia encontrada ha sido de 3.7%. Como alternativa a las nanoestructuras axiales de InGaN/GaN, la sección 4 presenta resultados sobre el crecimiento y caracterización de estructuras core-shell de InGaN/GaN, re-crecidas sobre arrays de micropilares de GaN fabricados por ataque de un template GaN/zafiro (aproximación top-down). El crecimiento de InGaN/GaN es conformal, con componentes axiales y radiales en el crecimiento, que dan lugar a la estructuras core-shell con claras facetas hexagonales. El crecimiento radial (shell) se ve confirmado por medidas de catodoluminiscencia con resolución espacial efectuadas en un microscopio electrónico de barrido, asi como por medidas de microscopía de transmisión de electrones. Más adelante, el crecimiento de micro-pilares core-shell de InGaN se realizó en pilares GaN (cores) crecidos selectivamente por epitaxia de metal-orgánicos en fase vapor. Con el crecimiento de InGaN se forman estructuras core-shell con emisión alrededor de 3 eV. Medidas de catodoluminiscencia resuelta espacialmente indican un aumento en el contenido de indio del shell en dirección a la parte superior del pilar, que se manifiesta en un desplazamiento de la emisión de 3.2 eV en la parte inferior, a 3.0 eV en la parte superior del shell. Este desplazamiento está relacionado con variaciones locales de la razón III/V en las facetas laterales. Finalmente, se demuestra la fabricación de una estructura pin basada en estos pilares core-shell. Medidas de electroluminiscencia resuelta espacialmente, realizadas en pilares individuales, confirman que la electroluminiscencia proveniente del shell de InGaN (diodo lateral) está alrededor de 3.0 eV, mientras que la emisión desde la parte superior del pilar (diodo axial) está alrededor de 2.3 eV. Para finalizar, se presentan resultados sobre el crecimiento ordenado de GaN, con y sin inserciones de InGaN, en templates semi polares (GaN(11-22)/zafiro) y no polares (GaN(11-20)/zafiro). Tras el crecimiento ordenado, gran parte de los defectos presentes en los templates originales se ven reducidos, manifestándose en una gran mejora de las propiedades ópticas. En el caso de crecimiento selectivo sobre templates con orientación GaN(11-22), no polar, la formación de nanoestructuras con una particular morfología (baja relación entre crecimiento perpedicular frente a paralelo al plano) permite, a partir de la coalescencia de estas nanoestructuras, la fabricación de pseudo-templates no polares de GaN de alta calidad. ABSTRACT The aim of this work is to gain insight into the selective area growth of InGaN nanostructures by plasma assisted molecular beam epitaxy, focusing on their potential as building blocks for next generation LEDs. Several nanocolumn-based approaches such as standard axial InGaN/GaN structures, InGaN/GaN core-shell structures, or InGaN/GaN nanostructures grown on semi- and non-polar substrates are discussed. The first section reviews the basics of the self-assembled growth of GaN nanocolumns on Si(111). Morphology differences and optical properties are compared to those of GaN layer grown directly on Si(111). The effects of the growth temperature on the In incorporation in self-assembled InGaN nanocolumns grown on Si(111) is described. The second section reviews the basic growth mechanisms of selectively grown GaNbased nanostructures on c-plane GaN/sapphire templates. By increasing the local III/V ratio morphological changes from pyramidal islands, to GaN nanocolumns with top semi-polar planes, and further to GaN nanocolumns with top polar c-planes are observed. When growing InGaN nano-disks embedded into the GaN nanocolumns, the different morphologies mentioned lead to different optical properties, due to the semipolar and polar nature of the crystal planes involved. The third section reports on the effect of the growth temperature and In/Ga ratio on the morphology and light emission characteristics of ordered InGaN nanocolumns grown on c-plane GaN/sapphire templates. Within the growth temperature range of 650 to 750oC the In incorporation can be modified either by the growth temperature, or the In/Ga ratio. Control of these factors allows the optimization of the InGaN nanocolumns light emission wavelength. In order to achieve white light emission two approaches are used. First yellow-white light emission can be obtained at room temperature from nanostructures where the InGaN region is composition-graded by using temperature gradients during growth. In a second approach the stacking of red, green and blue emitting segments was used to achieve the monolithic integration of these structures in one single InGaN nanocolumn leading to ordered broad spectrum emitters. With this approach, the spectral shape can be controlled by changing the thickness of the respective InGaN segments. Furthermore the growth of ordered arrays of InGaN/GaN nanocolumnar light emitting diodes by molecular beam epitaxy, emitting in the blue (441 nm), green (502 nm), and yellow (568 nm) spectral range is reported. The device active region, consisting of a nanocolumnar InGaN section of nominally constant composition and 250 to 500 nm length, is free of extended defects, which is in strong contrast to InGaN layers (planar) of similar composition and thickness. Electroluminescence spectra show a very small blue shift with increasing current, (almost negligible in the yellow device) and line widths slightly broader than those of state-of-the-art InGaN quantum wells. Next the selective area growth of In(Ga)N/GaN nanocolumns on Si(111) substrates is discussed. Ordered In(Ga)N/GaN nanocolumns emitting from ultraviolet (3.2 eV) to infrared (0.78 eV) were then grown on top of GaN-buffered Si substrates. The morphology and the emission efficiency of the In(Ga)N/GaN nanocolumns emitting in the green could be substantially improved by tuning the In/Ga and total III/N ratios, where an estimated internal quantum efficiency of 30 % was derived from photoluminescence data. In the next section, this work presents a study on the selective area growth mechanisms of green-emitting InGaN/GaN nanocolumns and their optical properties. InGaN/GaN nanocolumns with long InGaN sections (330-830nm) were grown on GaN/sapphire and GaN-buffered Si(111). The nanocolumn’s morphology and spatial indium distribution is found to depend on the local group (III)/N and In/Ga ratios at the nanocolumn’s top. A negligible spread of the average indium incorporation among different nanostructures is found as indicated by similar shapes of the cathodoluminescence spectra taken from single nanocolumns and ensembles of nanocolumns. For InGaN/GaN nanocolumns grown on GaN-buffered Si(111), all emitting in the green spectral range, the internal quantum efficiency increases up to 30% when decreasing growth temperature and increasing active nitrogen. This behavior is likely due to the formation of highly localized states, as indicated by the absence of a complete s-shape behavior of the PL peak position with temperature (up to room temperature) in samples with high internal quantum efficiency. On the other hand, no dependence of the internal quantum efficiency on the growth conditions is found for InGaN/GaN nanostructures grown on GaN/sapphire, where the maximum achieved efficiency is 3.7%. As alternative to axial InGaN/GaN nanostructures, section 4 reports on the growth and characterization of InGaN/GaN core-shell structures on an ordered array of top-down patterned GaN microrods etched from a GaN/sapphire template. Growth of InGaN/GaN is conformal, with axial and radial growth components leading to core-shell structures with clear hexagonal facets. The radial InGaN growth (shell) is confirmed by spatially resolved cathodoluminescence performed in a scanning electron microscopy as well as in scanning transmission electron microscopy. Furthermore the growth of InGaN core-shell micro pillars using an ordered array of GaN cores grown by metal organic vapor phase epitaxy as a template is demonstrated. Upon InGaN overgrowth core-shell structures with emission at around 3.0 eV are formed. With spatially resolved cathodoluminescence, an increasing In content towards the pillar top is found to be present in the InGaN shell, as indicated by a shift of CL peak position from 3.2 eV at the shell bottom to 3.0 eV at the shell top. This shift is related to variations of the local III/V ratio at the side facets. Further, the successful fabrication of a core-shell pin diode structure is demonstrated. Spatially resolved electroluminescence measurements performed on individual micro LEDs, confirm emission from the InGaN shell (lateral diode) at around 3.0 eV, as well as from the pillar top facet (axial diode) at around 2.3 eV. Finally, this work reports on the selective area growth of GaN, with and without InGaN insertion, on semi-polar (11-22) and non-polar (11-20) templates. Upon SAG the high defect density present in the GaN templates is strongly reduced as indicated by TEM and a dramatic improvement of the optical properties. In case of SAG on non-polar (11-22) templates the formation of nanostructures with a low aspect ratio took place allowing for the fabrication of high-quality, non-polar GaN pseudo-templates by coalescence of the nanostructures.

El vidrio y sus máscaras : el sueño de la arquitectura de cristal

Según Heidegger, la esencia de la arquitectura, de la construcción, descansa en un no espacio: en la materia con que se construyen las fronteras que otorgan espacios, irradiando sobre ellos aquello que los caracteriza. Si hay alguna materia, de las utilizadas por la arquitectura a lo largo de su historia para construir fronteras, que haya mantenido una especial relación con la luz y la visión, dando un carácter inconfundible a los espacios aviados por ellas, esta es el vidrio; algunas de las etimologías de su nombre: zakû (ser claro), hyalos (diáfano) o vitrum (ver), así lo evidencian. Posiblemente, sea la pregnancia de este modo fascinante de relacionarse con la luz, la que ha hecho del vidrio, a lo largo del tiempo que lleva siendo usado en arquitectura, y aún antes, el material que ha provocado en el imaginario humano la ilusión de ser aquel en que, en último término, podrían llegar a sublimarse todos los demás, dando lugar con ello a lo que en la tesis hemos denominado el sueño de la arquitectura de cristal. Siendo la luz, siempre, energía, consideraremos en la tesis luz-energía, a aquella que ilumina y calienta; es una luz científica y mesurable. Cuando la luz se “hace visible”, desvelando un mensaje “contenido” en el vidrio, hablaremos de luz-información. Esta luz, no puede medirse científicamente. La luz-energía y la luz-información, se manifiestan al conjuro de la arquitectura de vidrio. Es la segunda la que ha conformado las fronteras de vidrio enmascarado, y la que se estudia con más detenimiento en la tesis. Los distintos modos de usar en arquitectura la infinita combinatoria de las propiedades de absortancia, reflectancia, transmitancia y translucencia del vidrio, ha condicionado al hombre en su manera de “ver” el mundo. Unas veces, “inmerso” en él, puesto que solo lo separa del mismo, una frontera transparente, y “deseadamente” invisible: ese modo de usar el vidrio, ha sido el sueño imposible de una parte importante de la arquitectura del siglo XX. Otras veces, para “aislarse” de él, el hombre ha manipulado la luz y el vidrio para construir mundos diferentes. Las fronteras de vidrio enmascarado de color, mosaicos, vidrieras, pantallas y lo que hemos llamado vidrios complejos (con un cometido similar al que Schiller atribuía al coro en la tragedia griega, aislar a esta del “mundo real”, para mantener su libertad poética), son las fronteras que han construido el sueño posible de la arquitectura de cristal. Ambas actitudes, en distintos momentos de la historia de la arquitectura, han sido dos formas de querer materializar un mismo sueño. La capacidad del vidrio para adaptarse a tantos modos de presentarse ante nosotros, y a poder ser interpretado de tantas formas diferentes, es la que ha servido para dar título a la tesis, pues hasta en su faceta más transparente, el vidrio, de una forma o de otra, se ha mostrado siempre como un material enmascarado en el más amplio sentido de la palabra: se enmascara, incluso cuando apela a la transparencia o se convierte en espejo, para hacernos caer en la ilusión de que no está presente. Cuando el hombre construyó fronteras de vidrio e incluso antes, cuando soñó que con él podría llegar a construirlas, condensó en ellas toda la mítica, la mística y la epistemología en torno a la luz y la visión, dando lugar a una serie de arquetipos arquitectónicos. En la iglesia bizantina, la luz sobre, o la luz desde, los mosaicos, construyó una frontera titilante; y en la catedral gótica, la luz a través de las vidrieras construyó una frontera radiante; en ambos casos con el fin de alcanzar anagógicamente lo Inteligible. En el siglo XIX, con el descubrimiento de la electricidad y su incorporación a la arquitectura, las fronteras se vuelven fulgurantes, aviando, en este caso, el espacio urbano. Poco antes, en este mismo siglo, el espíritu del gótico tiene un efímero resurgir del que se nutrirá, a comienzos del siglo XX, el expresionismo cristalino, en el que la luz anagógica se hace laica. El espacio urbano fulgurante prefigurado por este movimiento y presente en las ciudades desde principios del siglo XX, fue potenciado a mediados de ese siglo con la aparición de las pantallas, extendiéndose desde entonces, imparable, por todo el planeta. La reciente emergencia de los vidrios complejos, ha abierto la posibilidad de construir fronteras a la carta (de vidrios de propiedades múltiples, seleccionadas de forma voluntaria y variable en cada momento). En principio, se pensó que, el uso de estos vidrios como cerramiento, podría llegar a constituirse como la panacea de los problemas del material relacionados con la luz-energía, sin necesidad de recurrir a “prótesis”, y manteniendo por tanto la seductora tersura de la fachada; aunque parece que, por ahora, esa posibilidad es, cuando menos, lejana. Sin embargo, en el campo de las megapantallas urbanas (y ,en general, en el de las pantallas de información), ubicuas actualmente en nuestras vidas, los vidrios complejos ayudan a construir los espesos velos de ilusión, que según Lefebvre sirven para mantener el capitalismo, siendo el último estadio de un desarrollo tecnológico, impuesto por el principio de economía del hombre, que como un metrónomo inexorable, y a modo de contrapunto, ha acompañado siempre (de nuevo en palabras de Lefebvre), a la necesidad del gasto, del juego, de la lucha, del arte, de la fiesta. La tecnología y el arte forman parte de la cultura producida por la sociedad y como señala Lévi-Strauss, esa cultura imprime orden; por el contrario, la sociedad, entendida como el conjunto de relaciones que los hombres mantienen entre sí, produce desorden. Del equilibrio entre esos extremos, surge el progreso, incluido el de la arquitectura. Las fronteras de vidrio que analizamos en la tesis –que avían espacios para la espiritualidad, el fasto y el espectáculo o, desde otro punto de vista, para las distintas manifestaciones del poder: la iglesia, la monarquía, el estado o el mercado– también han surgido de esa concomitancia entre el desorden y el orden; y forma parte de ese desorden, la aventura que ha impulsado al genio individual de místicos, alquimistas, geómetras, abades, reyes, inventores, poetas y arquitectos, a explorar, como escribe Apollinaire, vastos y extraños territorios donde el misterio en flor, se ofrece a quien quiera cogerlo, hogueras nuevas de colores nunca vistos, mil fantasmas imponderables a los que dar cuerpo. ABSTRACT According to Heidegger, the essence of architecture, building, lies in a non-space: the material that creates the boundaries from which something begins its presencing, radiating onto them that which characterizes them. If there is any single material amongst all those used throughout the history of architecture to build boundaries which has maintained a special relationship with light and vision, which has bestowed a distinctive character on spaces avid for them, it is glass. This is evidenced in some of its etymologies: zakû (to be clear), hyalos (transparent), vitrum (see). The rich potential of this fascinating way of relating to light in the history of the architectural use of glass, and even before, is possibly what has triggered the illusion in human imagination of being something that can ultimately sublimate all others, giving rise to what in this thesis we call The Dream of Crystal Architecture. Given that light is always energy, in this thesis we consider energy-light to be that which illuminates and warms. This is scientific, measurable light. When light "becomes visible" and reveals a message “contained” in glass, we speak of information-light. This light cannot be measured scientifically. Energy-light and information-light are manifested under the spell of glass architecture. The latter is what has shaped the boundaries of coloured glass, which is studied in this thesis. Architecture's different ways of using the infinite combinations of the absorptance, reflectance, transmittance and translucency of glass has affected the way we humans "see" the world. Sometimes we are "immersed" in it, since only an invisible, transparent boundary separates us from it: this use of glass has characterized a considerable part of 20th century architecture. In other cases, in order to "isolate" us from it, we have manipulated light and glass to build different worlds: the boundaries of glass "masked" by colour, mosaics, stained glass, screens and what we have called complex glazing, which plays a similar role to what Schiller attributed to the chorus in Greek tragedy, isolating it from the "real world" in order to maintain its poetic license. These are the boundaries that have built the viable dream of crystal architecture. These two approaches have been different ways of making same dream come true at different times in the history of architecture. The ability of glass to adapt to so many forms of manifestation, and interpretation, is what has given rise to the title of the thesis. Even in its most transparent facet, glass has one way or another always been a masking material in the broadest sense of the word: it is masked even when it invites transparency or becomes a mirror, triggering the illusion that it is not present. When man began to build glass boundaries, and even before, when he dreamed that he could build them, he condensed in them all the mythology, mysticism and epistemology concerning light and vision, which gave rise to a series of architectural archetypes. In the Byzantine church, light on or from mosaics created tenuous boundaries. In Gothic cathedrals, the light through the stained glass windows constructed radiant boundaries. In both cases the aim was to achieve, in an anagogical way, the Intelligible. In the 19th, the discovery of electricity and its use in architecture led to the production of dazzling boundaries, in this case employed in urban spaces. Earlier in the same century, the Gothic spirit had a short-lived revival, which in the early 20th century drew from crystalline expressionism in which anagogic light became secular. The dazzling urban space prefigured by this movement, present in cities since the early 20th century, was intensified in the mid-century with the emergence of screens, and since then it has spread unstoppably across the world. The recent emergence of complex glasses has made it possible to build boundaries on demand in glass with multiple properties, chosen at will and at whim at any time. Initially it was thought that the use of this glass as a wall could eventually become the panacea for the material problems related to energy-light, without needing to resort to "prosthesis" and thereby maintain the seductive smoothness of the facade. For now, that possibility seems remote, to say the least. In the realm of urban megascreens and information screens in general, now ubiquitous in our lives, complex glasses help to build the thick veils of illusion which, according to Lefebvre, serve to maintain capitalism. Like an inexorable metronome, in counterpoint, this ultimate state of technological development imposed by man's principle of economy has in fact always accompanied (again in the words of Lefebvre), the need to spend, play, fight, art, and party. Technology and art are part of the culture produced by society. As Levi-Strauss says, this culture imposes order. On the contrary, society, understood as a set of relationships amongst people, produces disorder. Progress, including that of architecture, arises from the balance between these two extremes. The glass boundaries analyzed in this thesis, which propitiate spaces for spirituality, pomp and spectacle or, from a different perspective, for the various manifestations of power: the church, the monarchy, the state and the market, have also emerged from the concomitance of order and disorder. One aspect of this disorder is the adventure that has inspired the individual genius of mystics, alchemists, surveyors, abbots, kings, inventors, poets and architects to explore, as Apollinaire says, vast, strange domains where flowering mystery offers itself to whoever wishes to pluck it, new fires, colours you have never seen before, a thousand intangible phantasms still awaiting reality.