Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Lighting”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18Linked to original sources
PubMed1991

Mouse kappa light-chain recombination signal sequences mediate recombination more frequently than do those of lambda light chain.

Immunoglobulin and T-cell receptor genes are somatically rearranged by site-specific recombination. Recombination signal sequences (RSS) have been identified as the major targeting element of this process. Recent reports demonstrate that differences in RSS affect the frequency of recombination, suggesting a role for RSS in the development of the B-cell repertoire. Examination of mouse light-chain RSS indicates that kappa light-chain RSS consistently show a greater degree of similarity to a consensus sequence than do those of lambda light chain. To determine whether this difference in natural RSS could affect the patterns of light-chain gene rearrangement and expression, we have constructed recombination substrates containing both a typical mouse kappa RSS pair and a typical mouse lambda RSS pair. Experiments using these substrates demonstrate that the kappa RSS pair mediates recombination at a vastly higher frequency than does the lambda RSS pair. This result argues that RSS differences may contribute significantly to the patterns of mouse immunoglobulin light-chain rearrangement, ultimately resulting in a high proportion of kappa light chain relative to lambda.

Animals↗
PubMed1995

A chimeric light-regulated amino acid transport system allows the isolation of blue light regulator (blr) mutants of Neurospora crassa.

We have developed a system for the isolation of Neurospora crassa mutants that shows altered responses to blue light. To this end we have used the light-regulated promoter of the albino-3 gene fused to the neutral amino acid permease gene mtr. The product of the mtr gene is required for the uptake of neutral aliphatic and aromatic amino acids, as well as toxic analogs such as p-flurophenylalanine or 4-methyltryptophan. mtr trp-2-carrying cells were transformed with the al-3 promoter-mtr wild-type gene (al-3p-mtr+) to obtain a strain with a light-regulated tryptophan uptake. This strain is sensitive to p-fluorophenylalanine when grown under illumination and resistant when grown in the dark. UV mutagenesis of the al-3p-mtr(+)-carrying strain allowed us to isolate two mutant strains, BLR-1 and BLR-2 (blue light regulator), that are light-resistant to p-fluorophenylalanine and have lost the ability to grow on tryptophan. These two strains have a pale-orange phenotype and show down-regulation of all the photoregulated genes tested (al-3, al-1, con-8, and con-10). Mutations in the BLR strains are not allelic with white collar 1 or white collar 2, regulatory genes that are also involved in the response to blue light.

Amino Acid Transport Systems↗
PubMed1999

LOV (light, oxygen, or voltage) domains of the blue-light photoreceptor phototropin (nph1): binding sites for the chromophore flavin mononucleotide.

Phototropism, the bending response of plant organs to or away from a directional light source, is one of the best studied blue light responses in plants. Although phototropism has been studied for more than a century, recent advances have improved our understanding of the underlying signaling mechanisms involved. The NPH1 gene of Arabidopsis thaliana encodes a blue light-dependent autophosphorylating protein kinase with the properties of a photoreceptor for phototropism. NPH1 apoprotein noncovalently binds FMN to form the holoprotein nph1. The N-terminal region of the protein contains two LOV (light, oxygen, or voltage) domains that share homology with sensor proteins from a diverse group of organisms. These include the bacterial proteins NIFL and AER, both of which bind FAD, and the phy3 photoreceptor from Adiantium capillus-veneris. The LOV domain has therefore been proposed to reflect a flavin-binding site, regulating nph1 kinase activity in response to blue light-induced redox changes. Herein we demonstrate that the LOV domains of two nph1 proteins and phy3 bind stoichiometric amounts of FMN when expressed in Escherichia coli. The spectral properties of the chromopeptides are similar to the action spectrum for phototropism, implying that the LOV domain binds FMN to function as a light sensor. Thus, our findings support the earlier model that nph1 is a dual-chromophoric flavoprotein photoreceptor regulating phototropic responses in higher plants. We therefore propose the name phototropin to designate the nph1 holoprotein.

Arabidopsis↗
PubMed1995

Oscillations of reaction center II-D1 protein degradation in vivo induced by repetitive light flashes. Correlation between the level of RCII-QB- and protein degradation in low light.

The D1 protein subunit of the photochemical reaction center II (RCII) turns over rapidly in oxygenic photosynthetic organisms exposed to the light. At high photon flux densities (PFD), photoinactivation of RCII precedes the degradation of the D1 protein. We found that the apparent quantum yield for the D1 protein degradation in Chlamydomonas cells is severalfold higher at low PFDs (10-100 mumol m-2 s-1) as compared to that observed at PFDs which induce photoinactivation of RCII (1.5-3 x 10(3) mumol m-2 s-1). Relative high levels of reduced RCII secondary plastoquinone acceptor, QB-, are induced in cells exposed to low PFDs as determined by thermoluminescence measurements. The probability of generating elevated levels of QB- which may recombine with the S2,3 oxidized states of the oxygen evolving complex decreases with increase in the light intensities at which consecutive double reduction of QB and exchange with the plastoquinone pool prevail. We have used light flashes to test if a correlation exists between the degradation of D1 protein and the relative level of QB-. D1 protein degradation could be induced in dark-incubated cells exposed to a series of 1.4 x 10(3) single light flashes given at intervals compatible with generation of elevated levels of QB- and its decay by charge recombination. Oscillations of the QB- level in cells exposed to 960-1440 series of 1 to several flashes correlated with oscillations of the D1 protein degradation in Chlamydomonas cells and in the Scenedesmus wild type but not in the LF-1 mutant lacking photosystem II donor side activity. In this mutant the "S state cycle" and QB- oscillations are abolished. We propose that the process of recombination of long lived RCII-QB- with the S2,3 states may involve damaging events related to the D1 protein degradation induced by light flashes or continuous low light in vivo.

Animals↗
PubMed1983

Light and dark adaptation in Phycomyces light-growth response.

Sporangiophores of the fungus Phycomyces exhibit adaptation to light stimuli over a dynamic range of 10(10). This range applies to both phototropism and the closely related light-growth response; in the latter response, the elongation rate is modulated transiently by changes in the light intensity. We have performed light- and dark-adaptation experiments on growing sporangiophores using an automated tracking machine that allows a continuous measurement of growth velocity under controlled conditions. The results are examined in terms of the adaptation model of Delbrück and Reichardt (1956, Cellular Mechanisms in Differentiation and Growth, 3-44). The "level of adaptation," A, was inferred from responses to test pulses of light by means of a series of intensity-response curves. For dark adaptation to steps down in the normal intensity range (10(-6)-10(-2) W/m2), A decays exponentially with a time constant b = 6.1 +/- 0.3 min. This result is in agreement with the model. Higher-order kinetics are indicated, however, for dark adaptation in the high-intensity range (10(-2)-1 W/m2). Adaptation in this range is compared with predictions of a model relating changes in A to the inactivation and recovery of a receptor pigment. In response to steps up in intensity in the normal range, A was found to increase rapidly, overshoot the applied intensity level, and then relax to that level within 40 min. These results are incompatible with the Delbrück-Reichardt model or any simple generalizations of it. The asymmetry and overshoot are similar to adaptation phenomena observed in systems as diverse as bacterial chemotaxis and human vision. It appears likely that light and dark adaptation in Phycomyces are mediated by altogether different processes.

Adaptation, Biological↗
PubMed2000

High-angle scattering events strongly affect light collection in clinically relevant measurement geometries for light transport through tissue.

Measurement of light transport in tissue has the potential to be an inexpensive and practical tool for non-invasive tissue diagnosis in medical applications because it can provide information on both morphological and biochemical properties. To capitalize on the potential of light transport as a diagnostic tool, an understanding of what information can be gleaned from light transport measurements is needed. We present data concerning the sensitivity of light transport measurements, made in clinically relevant geometries, to scattering properties. The intensity of the backscattered light at small source-detector separations is shown to be sensitive to the phase function, and furthermore the collected light intensity is found to be correlated with the amount of high-angle scattering in the medium.

Biophysical Phenomena↗
PubMed2004

Nitrogen- and storage-affected carbohydrate partitioning in high-light-adapted Pelargonium cuttings in relation to survival and adventitious root formation under low light.

BACKGROUND AND AIMS: The aim of this study was to determine the role of nitrogen- and storage-affected carbohydrate availability in rooting of pelargonium cuttings, focusing on the environmental conditions of stock plant cultivation at low latitudes, transport of cuttings, and rooting under the low light that prevails during the winter rooting period in Central European greenhouses. METHODS: Carbohydrate partitioning in high-light-adapted cuttings of the cultivar 'Isabell' was studied in relation to survival and adventitious root formation under low light. Effects of a graduated supply of mineral nitrogen to stock plants and of cutting storage were examined. KEY RESULTS: Nitrogen deficiency raised starch levels in excised cuttings, whereas the concentrations of glucose and total sugars in leaves and the basal stem were positively correlated with internal total nitrogen (Nt). Storage reduced starch to trace levels in all leaves, but sugar levels were only reduced in tissues of non-nitrogen deficient cuttings. Sugars accumulated in the leaf lamina of stored cuttings during the rooting period, whereas carbohydrates were simultaneously exhausted in all other cutting parts including the petioles, thereby promoting leaf senescence. The positive correlation between initial Nt and root number disappeared after storage. Irrespectively of storage, higher pre-rooting leaf glucose promoted subsequent sugar accumulation in the basal stem and final root number. The positive relationships between initial sugar levels in the stems with cutting survival and in leaves with root formation under low light were confirmed in a sample survey with 21 cultivars provided from different sources at low latitudes. CONCLUSIONS: The results indicate that adventitious rooting of pelargonium cuttings can be limited by the initial amount of nitrogen reserves. However, this relationship reveals only small plasticity and is superimposed by a predominant effect of carbohydrate availability that depends on the initial leaf sugar levels, when high-light adaptation and low current light conditions impair net carbon assimilation.

Adaptation, Physiological↗
PubMed1997

White collar 2, a partner in blue-light signal transduction, controlling expression of light-regulated genes in Neurospora crassa.

A saturating genetic dissection of 'blind' mutants in Neurospora crassa has identified a total of two non-redundant loci (wc-1 and wc-2) each of which is required for blue-light perception/signal transduction. Previously, we demonstrated that WC1 is a putative zinc finger transcription factor able to bind specifically to a light-regulated promoter. Here, we present the cloning and characterization of the wc-2 gene. We demonstrate using mutation analysis and in vitro DNA-binding assays that WC2, the second partner of this light signal transduction system, encodes a functional zinc finger DNA-binding protein with putative PAS dimerization and transcription activation domains. This molecular genetic dissection of the second of two components of this light signal transduction system has enabled us to devise a model whereby WC1 and WC2 are proposed to interact via homologous PAS domains, bind to promoters of light-regulated genes and activate transcription. As such, this study provides the first insight into two co-operating partners in blue-light signal transduction in any organism and describes the molecular tools with which to dissect this enigmatic process.

Amino Acid Sequence↗
PubMed2005

Stromal over-reduction by high-light stress as measured by decreases in P700 oxidation by far-red light and its physiological relevance.

The oxidation level of P700 induced by far-red light (DeltaA(FR)) in briefly dark-treated leaves of some sun plants decreased during the daytime and recovered at night. The dark recovery of decreased DeltaA(FR) proceeded slowly, with a half-time of about 5 h. We propose that stromal over-reduction induced by sunlight was the direct cause of the depression of DeltaA(FR). The depression of DeltaA(FR) found during the daytime was reproduced by controlled illumination with saturating light of fully dark-treated leaves. Simultaneous measurement of P700 redox and chlorophyll fluorescence showed that the depression of DeltaA(FR) was associated with dark reduction of the plastoquinone pool, which represented cyclic electron transport activity. The decrease of DeltaA(FR) in the light-stressed chloroplasts was partly reversed by treatment with 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, an inhibitor of electron transport at the cytochrome b6/f complex, and the subsequent addition of methyl viologen, an efficient electron acceptor from photosystem I (PSI), stimulated further recovery, showing that both cyclic electron flow around PSI and the charge recombination within PSI were responsible for the light-induced depression of DeltaA(FR). The dark level of blue-green fluorescence, an indicator of NAD(P)H concentration, from intact chloroplasts was increased by high-light stress, suggesting that NADPH accumulated in stroma as a result of the high-light treatment. Possible effects on photosynthetic activity of over-reduction and its physiological relevance are discussed.

Chlorophyll↗
PubMed2003

How light irradiance and curing time affect monomer conversion in light-cured resin composites.

We tested the hypothesis that the degree of conversion of a light-cured dental composite relates to the calculated (s x mW cm-2 = mJ cm-2) rather than to the irradiance value (mW cm-2) of the light source. Two light-curable composite resins were cured with three different light irradiance values over different curing times. The specimens tested were 2, 4 or 6 mm thick, and the degree of conversion values were measured with Raman spectroscopy on the top and the bottom surfaces of the specimens. The highest conversion value of one of the materials was just below 60%, while the maximal conversion value of the other material was just below 65%. That difference in conversion values could be related to differences in monomer systems used in the two composites. By considering light energy per square centimeter (J cm-2) rather than light irradiance (mW cm-2), we found that equivalent energy values gave similar conversion values for a certain sample thickness. From these findings, we conclude that our experimental results support our hypothesis.

Composite Resins↗
PubMed2004

The effect of sterilization methods on the light transmission characteristics and structure of light-curing tips.

The purpose of this study was to investigate the effect of various sterilization methods on the light transmission and the structural characteristics of two light-curing tips. Twenty tips from two light-curing devices [Elipar II (EL) and Heliolux II (HL)] were classified into four groups. The tips in groups A to C were subjected to sterilization with 0.2% sodium dichloroisacyanurate solution (Presept), 2% glutaraldehyde solution (Cidex) (2 h cycle(-1)) and water-steam autoclave (120 degrees C, 1 bar, 12 min cycle(-1)), respectively. A total of 2100 sterilization cycles was performed for all methods tested. The transmitted light intensity (TLI) was measured at specific sterilization time intervals by a curing radiometer (Model 100, Demetron). The final % TLI reduction of the sterilized tips was calculated relative to the corresponding control ones. The topography and composition of the front curing tip surfaces were determined using scanning electron microscopy combined with electron probe microanalyser. Autoclaving caused the lowest final TLI decrease (EL: 15%, HL: 19%) compared with Presept (EL: 60%, HL: 42%) and with Cidex (EL: 68%, HL: 52%). Cidex yielded higher TLI drop than Presept for both types of tips examined. Elipar tips were found to be more sensitive than Heliolux tips to both chemical sterilization techniques. Total or partial coating of the tip surfaces with insoluble salts after sterilization with Presept and Cidex was detected, mainly composed of Ca, Cl, Al, Pd and Mg traces. No changes were noted on the surfaces after autoclave. Water-steam autoclave is safer than the 0.2% sodium dicloroisocyanorate and 2% glutaraldehyde chemical sterilization agents regarding the light transmission characteristics and the structure of the light-curing tips.

Dental Disinfectants↗
PubMed2005

Protein kinase C modulates light responses in Neurospora by regulating the blue light photoreceptor WC-1.

The Neurospora protein kinase C (NPKC) is a regulator of light responsive genes. We have studied the function of NPKC in light response by investigating its biochemical and functional interaction with the blue light photoreceptor white-collar 1 (WC-1), showing that activation of NPKC leads to a significant decrease in WC-1 protein levels. Furthermore, we show that WC-1 and NPKC interact in a light-regulated manner in vivo, and that protein kinase C (PKC) phosphorylates WC-1 in vitro. We designed dominant negative and constitutively active forms of PKC which are able to induce either a large increase of WC-1 protein level or a strong reduction respectively. Moreover, these changes in PKC activity result in an altered light response. As WC-1 is a key component of Neurospora circadian clock and regulates the clock oscillator component FRQ we investigated the effect of NPKC-mutated forms on FRQ levels. We show that changes in PKC activity affect FRQ levels and the robustness of the circadian clock. Together these data identify NPKC as a novel component of the Neurospora light signal transduction pathway that modulates the circadian clock.

Circadian Rhythm↗
PubMed2006

Regulation by blue light and heat shock of gene transcription in the fungus Phycomyces: proteins required for photoinduction and mechanism for adaptation to light.

The gene hspA for the heat-shock protein HSP100 is induced by blue light and heat shock in the zygomycete fungus Phycomyces blakesleeanus. We have investigated the molecular details of the regulation of hspA gene transcription. We have cloned 1.9 kb of hspA upstream DNA sequence and identified many DNA segments possibly involved in heat-shock and blue-light regulation. We have identified several gene products required for hspA photoactivation and found that they are also required for mycelial photoresponses, a suggestion for a common signal transduction pathway. In addition, we have found that beta-carotene, or a chemical derivative, is required for hspA gene photoactivation. The activation of hspA after blue light-exposure or a heat shock is transient, suggesting the adaptation to the stimulus. The adaptation of hspA photoactivation seems to be the result of a novel mechanism causing a light-dependent loss of gene transcription. We propose that a reduction in the amount of MADA, a putative flavin-binding zinc-finger protein, in light-exposed mycelia may cause a reduced hspA photoactivation, providing a simple explanation for adaptation to light.

Cloning, Molecular↗
PubMedDate not supplied

Green light is effective and less painful than red light in photodynamic therapy of facial solar keratoses.

Photodynamic therapy (PDT) with topically applied delta-aminolevulinic acid (ALA) is increasingly employed to treat patients with multiple solar keratoses and superficial skin tumors. For these indications, ALA-PDT has been shown to be highly efficient. Treatment of multiple or extended lesions, however, is substantially hampered by the fact that ALA-PDT is associated with burning pain during the irradiation procedure. The standard irradiation devices commonly used for ALA-PDT emit red light around 630 nm. In the present half-side comparison study we have observed that ALA-PDT employing a green light irradiation device (543-548 nm) is equally effective, as compared with standard red light ALA-PDT. In contrast to red light ALA-PDT, however, green light ALA-PDT caused only little tingling and burning but no pain. These observations indicate that green light ALA-PDT is superior to standard ALA-PDT, because it is associated with less unwanted side effects.

Aged↗
PubMed2001

The linearly polarized light field in clear, tropical marine waters: spatial and temporal variation of light intensity, degree of polarization and e-vector angle.

Sensitivity to polarized light is widespread among marine animals, including crustaceans, cephalopods and some fishes. They use this ability to orient and find prey, and possibly for a number of other visual tasks. Unlike the ultraviolet-sensitive polarization receptors of most insects, the polarization receptors of marine invertebrates tend to be maximally sensitive near 500 nm, suggesting that polarized light in water differs from that in air. The underwater field of partially linearly polarized light has been studied for nearly 50 years, but data are still limited and sparse. We measured the submarine polarized light field from 350 to 600 nm throughout the day on a coral reef in the Florida Keys at a depth of 15m using the underwater laboratory Aquarius as a research platform. Our results show that the angle of polarization as viewed along any given line of sight at this depth is a relatively simple function of solar position and that the degree of polarization is greatest 60-90 degrees from the sun. Both e-vector angle and degree of polarization vary only slightly with wavelength, although light is sometimes less polarized in the ultraviolet. Since light is most intense at medium wavelengths and polarization is nearly maximal at these wavelengths, invertebrate polarization photoreceptors are spectrally well placed. Also, the relative spectral constancy of the angle and degree of polarization supports fish polarization sensitivity, which relies on spectrally diverse photoreceptor sets.

Animals↗
PubMedDate not supplied

Comparative photobiology of growth responses to two UV-B wavebands and UV-C in dim-red-light- and white-light-grown cucumber (Cucumis sativus) seedlings: physiological evidence for photoreactivation.

We examined the influence of short-term exposures of different UV wavebands on the elongation and phototropic curvature of hypocotyls of cucumbers (Cucumis sativus L.) grown in white light (WL) and dim red light (DRL). We evaluated (1) whether different wavebands within the ultraviolet B (UV-B) region elicit different responses; (2) the hypocotyl elongation response elicited by ultraviolet C (UV-C); (3) whether irradiation with blue light-enriched white light (B/WL) given simultaneous with UV-B treatments reversed the effect of UV in a manner indicative of photoreactivation; and (4) whether responses in WL-grown plants were similar to those grown in DRL. Responses to brief (1-100 min) irradiations with three different UV wavebands all induced inhibition of elongation measured after 24 h. When WL-grown seedlings were irradiated with light containing proportionally greater short wavelength UV-B (37% of UV-B between 280 and 300 nm), inhibition of hypocotyl elongation was induced at a threshold of 0.5 kJ m(-2), whereas exposure to UV-B including only wavelengths longer than 290 nm (and only 8% of UV-B between 290 and 300 nm) induced inhibition of hypocotyl elongation at a threshold of 1.6 kJ m(-2). The UV-C treatment induced reduction in elongation at a threshold of <0.01 kJ m(-2) for DRL-grown plants and <0.03 kJ m(-2) for WL-grown plants. B/WL caused 50% reversal of the short-wavelength UV-B-induced inhibition of elongation in DRL-grown seedlings but did not reverse the effect of long-wavelength UV-B. B/WL caused 30% reversal of the UV-C-induced inhibition of elongation in WL-grown seedlings but did not affect the response to short-wavelength UV-B. Short-wavelength UV-B also induced positive phototropic curvature in both types of seedlings, and this was reversed 60% or completely in DRL-grown and WL-grown seedlings, respectively. The similarity of responses between the etiolated (DRL-grown) and de-etiolated (WL-grown) seedlings indicates that the short-wavelength specific response may be relevant to natural light environments, and the apparent photoreactivation implicates DNA damage as the sensory mechanism for the response.

Cucumis sativus↗
PubMed1991

Light chain deposition disease without detectable light chains in serum or urine. Report of a case and review of the literature.

A patient presenting with a nephrotic syndrome and chronic renal failure caused by light chain deposition disease (LCDD) without detectable light chains in serum and urine is presented. Only a few patients with LCDD but without detectable light chains in serum and urine have hitherto been reported. The diagnosis was made by light-microscopic and immunofluorescent examination of a percutaneous renal biopsy. The histological differential diagnosis of LCDD includes diabetic glomerulosclerosis, renal amyloidosis and membranoproliferative glomerulonephritis. For the histological diagnosis of LCDD, immunofluorescence using anti-kappa and anti-lambda antisera is essential. Although renal involvement is a constant feature in LCDD, other sites of deposition of light chains have been reported. The absence of detectable light chains in serum or urine is discussed.

Biopsy↗
PubMed1980

Nodular glomerulopathy associated with nonamyloidotic kappa light chain deposits and excess immunoglobulin light chain synthesis.

A nodular glomerulopathy characterized by mesangial deposits of monoclonal kappa light chains was detected by immunofluorescence in a renal biopsy from a patient with proteinuria and hypertension. These nodules lacked the tinctorial and morphologic features of amyloid. Ultrastructurally, the nodules contained electron-dense granular deposits as well as fibrils in parallel arrangement. The fibrils measured 110-140 A in diameter. They were consistent in size with amyloid fibrils. However, they differed in lacking the randomly oriented network of typical amyloid fibrils and more closely resembled fibrils intrinsic to mesangial matrix. The patient had no bone marrow or X-ray evidence of myeloma and no evidence of free monoclonal light chains in serum or concentrated urines. Biosynthetic studies of the patient's bone marrow cells demonstrated unbalanced immunoglobulin synthesis with excess production of monoclonal kappa light chains. These observations suggest that the observed glomerulopathy results from direct deposition of monoclonal light chains. Deposits with kappa light chain determinants have been found in 7 other patients with similar nodular glomerulopathies, 4 of whom had diagnosed clinical myeloma. The lesion of nonamyloidotic nodular glomerulopathy previously described in 19 patients, nor examined by immunopathologic techniques or not shown to contain light chain determinants, may have a similar pathogenesis.

Adult↗