Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “light induction”

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 577 records · Page 32Linked to original sources
PubMed1970

Photoinhibition of growth in Acanthamoeba castellanii cultures.

Light from 350 to 680 nm at intensities up to 1.62 x 10(5) ergs per sec per cm(2) slowed exponential growth and lowered the maximum yield in axenic cultures of Acanthamoeba castellanii. Photoinhibition was a linear function of light intensity up to 1.25 x 10(5) ergs per sec per cm(2). At higher intensities, growth was too slow to be measured accurately. A photochemical change occurring in the growth medium on irradiation was a function of light dosage and not intensity per se. Light in dosages which appreciably changed the growth-supporting properties of the medium exceeded the dosages received by exponentially growing cultures during irradiation. Consequently, photoinhibition of growth was attributed to a direct effect of light on the amoebae, not to photodegradation of the medium. The growth-supporting properties of irradiated media could be restored by the addition of yeast extract and Proteose peptone. The reduced growth rate in the light was not due to cyst formation or induction of multinuclearity. Light affected the amoebae either through absorption by intracellular pigment(s) or through binding to the amoebae of a photosensitizing compound in the medium.

Culture Media↗
PubMed2004

Ultraviolet light-induced regulatory (suppressor) T cells: an approach for promoting induction of operational allograft tolerance?

Ultraviolet (UV) light is known to induce skin cancers by causing DNA gene mutations and inducing immunosuppression. Taking advantage of these immunosuppressive capacities, UV light has been used, with different modalities, as an immunosuppressive therapy in a variety of diseases including allograft rejection and graft-versus-host disease. Phototherapy includes UVB irradiation, UVA irradiation, oral psoralen (+)UVA irradiation (PUVA), photodynamic therapy, and extracorporeal photopheresis, which consists of infusion of UVA-irradiated autologous leukocytes collected by apheresis and incubated with 8-methoxypsoralen. According to numerous experimental models and human data, there is increasing evidence that UVB irradiation and extracorporeal photopheresis can induce regulatory T cells and anticlonotypic activity. These therapies induce apoptosis of activated T cells or of extracorporally treated mononuclear cells, and up-regulate the expression of costimulary molecules and adhesion molecules on antigen presenting cells. UVB- or UVA-induced apoptotic cells could secrete immune suppressive cytokines (interleukin (IL)-4, IL-10). The processing and presentation of apoptotic T cell antigens from clones of pathogenic T cells by activated antigen presenting cells might explain the induction of systemic anticlonotypic activity by photopheresis. This induction of cell-mediated suppressive activity opens up future prospects with the aim of expanding regulatory T cells and/or anticlonotypic activity, especially by photopheresis in organ and cell transplantation.

Animals↗
PubMedDate not supplied

[Fluorescence, excited by light in the 380-540 nm wavelength range, in in cucumber leaves depends on the time of vegetation and light regime].

The slow fluorescence induction produced in cucumber leaves by light in the range of wavelengths 380-540 nm and intensity of 180 W/m2 was studied. The ratio of fluorescence maxima in the red region (F734/F682) in young and mature leaves was approximately 2. It is assumed that this value depends on an increase in the contribution of the long-wavelength fluorescence due to the spillover effect. In plants grown under natural conditions, the parameter F734/F682 correlated with the concentrations of chlorophyll and carotenoids. In plants grown in the light of red and blue regions no such correlation was observed and the F734/F682 remained unchanged. It is concluded that the F534/F682 is affected by the intensity and spectral composition of exciting light used during the growing.

Carotenoids↗
PubMed1992

cis-urocanic acid suppression of contact hypersensitivity induction is mediated via tumor necrosis factor-alpha.

Ultraviolet B (UVB) light impairs the induction of contact hypersensitivity to epicutaneously applied haptens in certain strains of mice by a genetically determined mechanism that depends upon the participation of TNF-alpha. Because the superficial epidermis contains large amounts of trans-urocanic acid (trans-UCA), because exposure to UVB radiation converts this compound to cis-UCA, and because cis-UCA has been reported to be immunosuppressive, we have examined the possibility that the TNF-alpha-dependent effects of UVB on contact hypersensitivity induction in mice are mediated via conversion of trans- to cis-UCA. By injecting cis-UCA intradermally before application of dinitrofluorobenzene, by treating cis-UCA-injected mice systemically with neutralizing anti-TNF-alpha antibodies, and by comparing the consequences of these maneuvers in UVB-susceptible and UVB-resistant strains of mice, we have determined a) that cis-UCA can impair the induction of contact hypersensitivity in a manner similar to UVB radiation, and that the impairment is dependent upon TNF-alpha; b) that cis-UCA altered the morphology of epidermal Langerhans cells in a manner similar to UVB radiation, and that the alteration was dependent, in part, upon TNF-alpha; and c) that the inhibitory effects of cis-UCA on induction of contact hypersensitivity and the histologic effects of this compound on epidermal Langerhans cells appear to be influenced by alleles at the Tnf alpha and Lps loci. Based on these findings we propose that UVB radiation impairs the induction of contact hypersensitivity in mice by converting trans-urocanic acid to cis-UCA within the epidermis; cis-UCA in turn causes the local release of TNF-alpha, which thwarts sensitization by its ability to trap epidermal Langerhans cells transiently within the epidermis, and thereby prevents the immunogenic signal from reaching the draining lymph node where activation of unprimed, Ag-specific T cells must occur.

Animals↗
PubMed1993

Effects of nightbreak, T-cycle, and resonance lighting schedules on the pineal melatonin rhythm of the lizard Anolis carolinensis: correlations with the reproductive response.

Experiments were conducted to determine if a correlation exists between any aspect of the pineal melatonin rhythm (such as its duration or phase) in the lizard Anolis carolinensis and the reproductive response to photoperiod. The rhythm of pineal melatonin content was determined in anoles exposed to nightbreak lighting protocols (10L:5D:1L:8D, 10L:10D:1L:3D), resonance lighting cycles (LD 11:13, LD 11:25), and T-cycle lighting protocols (LD 11:7, LD 11:9, LD 11:13, LD 11:15, LD 11:19) and compared with the testicular response to these lighting protocols as determined previously [Underwood and Hyde, (1990) J. Comp. Physiol. (A) 167:231-243]. Different T-cycles and nightbreak cycles elicited changes in both the duration of the melatonin peak and the phase of the melatonin peak relative to these light cycles. The response to the resonance cycle (LD 11:25) was complex, probably due to the overlapping patterns of two groups whose pineal melatonin rhythms were entrained approximately 12 hr out of phase with each other. No correlation was observed between the duration, or the amplitude, of the nocturnal melatonin peaks seen on the various light cycles and the reproductive response to these cycles. A correlation was observed between the phase of the pineal melatonin rhythm and the reproductive response. Light cycles were inductive (stimulated testicular growth) when the entrained melatonin rhythm peaked near the light-to-dark or the dark-to-light transition, but they were not inductive when the melatonin rhythm peaked during the middle third of the night. These results suggest that if melatonin is involved in the transduction of photoperiodic information in Anolis, neither the duration nor amplitude of the nocturnal melatonin pulse is involved in the measurement of day length. Instead, the phase-relationship of the melatonin rhythm to the rest of the circadian system may determine photoperiodic responsiveness.

Animals↗
PubMed1996

fhy1 defines a branch point in phytochrome A signal transduction pathways for gene expression.

Physiological analysis of the fhy1 mutant of Arabidopsis has led to the proposal that the mutant is deficient in a downstream component of the phytochrome A signal transduction pathway. To define this lesion at the molecular level, we have examined the expression of a range of phytochrome-regulated genes in fhy1. In far-red light, the regulation of genes such as CHS and CHI is blocked in fhy1, whereas the induction of CAB and NR genes is affected minimally. In contrast, the induction of all genes tested is blocked in a phytochrome A-deficient mutant, confirming that gene expression in far-red light is regulated solely by phytochrome A. Thus, fhy1 defines a branch point in phytochrome A signal transduction pathways for gene expression. Contrary to the general opinion that responses to continuous red light are mediated by phytochrome B and other photostable phytochromes, we have shown also that red light-induction of CHS is mediated almost entirely by phytochrome A. Furthermore, phytochrome A-mediated induction of CHS by red light is blocked in fhy1. The induction of CHS by blue light, however, is normal in fhy1, suggesting that although FHY1 is a component of the phytochrome A signaling pathway, it is not a component of the blue-light signaling pathway for CHS expression.

Acyltransferases↗
PubMed1984

Stability of DNA in mammalian cells irradiated with near-uv light (uv-a).

The induction of lesions in human melanoma DNA by near-uv light (uv-a) has been investigated using a procedure to lyse the cells in dilute alkali. The alkaline treatment denatures the DNA, which results in fragmentation of the DNA in irradiated cells but not in control cells. The solution is neutralized to allow the larger fragments to renature. The smaller, single-stranded DNA fragments (2-10 kb) are then detected using agarose gel electrophoresis. With increasing dose of irradiation there are increasing amounts of the smaller fragments detected. The DNA fragmentation, which can be prevented by treating the cells with the radical scavenger DMSO, is not induced via the incubation medium. Hence uv-a has distinct effects on chromosomal DNA.

DNA, Neoplasm↗
PubMed1989

Blue light regulates the accumulation of two psbD-psbC transcripts in barley chloroplasts.

Synthesis of D2, a Photosystem II reaction center protein encoded by psbD, is differentially maintained during light-induced chloroplast maturation. The continued synthesis of D2 is paralleled by selective light-induced accumulation of two psbD-psbC transcripts which share a common 5' terminus. In the present study, we examine the nature of the photoreceptor and the fluence requirement for psbD-psbC transcript induction. The light-induced change in psbD-psbC RNA population can be detected between 1 and 2 h after 4.5 day old dark-grown barley seedlings are transferred to the light. Light-induced transcript accumulation occurs normally in the chlorophyll-deficient barley mutant, xan-f10, indicating that light-activated chlorophyll formation and photosynthesis are not required for RNA induction. High fluence blue light fully induces psbD-psbC transcript accumulation; low or high fluence red or far-red light do not. However, psbD-psbC transcript accumulation elicited by blue light pulses can be partially attenuated if far-red light is given immediately following the blue light treatment. Thus, although blue light is needed to initiate transcript accumulation, phytochrome modulates the amplitude of the response. Pretreatment of dark-grown plants with cycloheximide blocks light-induced psbD-psbC transcript accumulation. This could implicate a blue-light responsive nuclear gene in the light-induced accumulation of the two psbD-psbC transcripts.

4-Aminobutyrate Transaminase↗
PubMed1991

Induction of transverse polarity by blue light: an all-or-none response.

Phototropic stimulation induces a spatial memory. This was inferred from experiments with maize (Zea mays L.) coleoptiles involving opposing blue-light pulses, separated by variable time intervals, and rotation on a horizontal clinostat (Nick and Schafer, 1988b, Planta 175, 380-388). In those experiments, individual seedlings either curved towards the first or towards the second pulse, or they remained straight. Bending, if it occurred, seemed to be an all-or-none response. Intermediates, i.e. plants, bending only weakly, were not observed. In the first part of the present study it was attempted to create such intermediates. For this purpose the strength of the first, inducing, and the second, opposing, pulse was varied. The result was complex: (i) Individual seedlings maintained the all-or-none expression of spatial memory. (ii) However, on the level of the whole population, the time intervals at which a given response type dominated depended on the fluence ratio. (iii) Furthermore, the final curvature was determined by the fluence ratio. These results are discussed in terms of a blue-light-induced transverse polarity. This polarity initiates from a labile precursor, which can be reoriented by an opposing stimulation (indicated by the strong bending towards the second pulse). The strong curvatures towards the first pulse over long time intervals reveal that, eventually, the blue-light-induced transverse polarity becomes stabilised and thus immune to the counterpulse. In the second part of the study, the relation between phototropic transduction and transverse polarity was characterised by a phenomenological approach involving the following points: (i) Sensory adaptation for induction of transverse polarity disappears with a time course similar to that for phototropic sensory adaptatation. (ii) The fluence response for induction of transverse polarity is a saturation curve and not bell-shaped like the curve for phototropism (iii) For strong counterpulses and long time intervals the clinostat-elicited nastic response (Nick and Schafer 1989, Planta 179, 123-131) becomes manifest and causes an "aiming error" towards the caryopsis. (iv) Temperature-sensitivity of polarity induction was high in the first 20 min after induction, then dropped sharply and rose again with the approach of polarity fixation. (v) Stimulus-summation experiments indicated that, for different inducing fluences, the actual fixation of polarity happened at about 2 h after induction. These experiments point towards an early separation of the transduction chains mediating phototropism and transverse polarity, possibly before phototrophic asymmetry is formed.

Cell Polarity↗
PubMed2000

DNA DSB induction and rejoining in V79 cells irradiated with light ions: a constant field gel electrophoresis study.

PURPOSE: To study the induction and the time-course of rejoining of DNA double strand breaks (DSB) in V79 cells irradiated with light ions with different linear energy transfer (LET). MATERIALS AND METHODS: V79 cells were irradiated in monolayer with monoenergetic proton, deuteron, helium-3 or helium-4 ion beams, each at two different energy values. Gamma rays were used as reference radiation. DSB have been measured by constant field gel electrophoresis (CFGE). RESULTS: The initial yield depended little on the particle type and LET. The amount of DSB left unrejoined for up to 2 h incubation time could be roughly described by a decreasing exponential function with a final plateau, although more complex functions cannot be excluded. Radiation quality had little effect on the rejoining rate but affected the plateau. The amount of residual DSB after 2 h was higher for densely than for sparsely ionizing radiation, and for the same particle was dependent on LET. The corresponding RBE ranged from 1.8 to 6.0. CONCLUSIONS: The results support the hypothesis that complex, less reparable DSB are induced in higher proportion by light ions with respect to gamma-rays and that, for the same ion, increasing LET leads to an increase in this proportion.

Animals↗
PubMed1999

Identification of UV-B light-responsive regions in the promoter of the tryptophan decarboxylase gene from Catharanthus roseus.

The tryptophan decarboxylase (Tdc) gene encodes a key enzyme in the biosynthesis of terpenoid indole alkaloids (TIAs) in Catharanthus roseus. TIAs absorb ultraviolet light (UV) and putative functions in plants include a role as UV protectants. In support of this possible function we demonstrate here that UV light induces accumulation of several TIAs as well as expression of the Tdc gene in C. roseus. In addition, in tobacco a Tdc-gusA construct was found to be specifically induced by UV-B light. Lack of induction by UV-A or other wavelengths of light indicate that Tdc expression is regulated by a specific UV-B receptor and corresponding signal transduction pathway. To identify UV-responsive Tdc promoter elements, a loss-of-function analysis was performed, in which deletion derivatives were fused to the gusA reporter gene and analysed in transgenic tobacco plants. Truncation of the Tdc promoter from -1818 (relative to the start of transcription) to -160 reduced expression levels two-fold without affecting the qualitative UV response. Deletion to -37 further reduced expression levels five-fold, but the delta37 promoter also remained UV-responsive. Subsequently, the -160 to -37 region was further studied by gain-of-function experiments, in which the transcriptional activities of tetramerized subfragments fused to truncated promoters were analysed. Combination of the data identified several functional regions in the -160 to +198 promoter. The - 160 to -99 region acts as the main transcriptional enhancer. UV-responsive elements appeared to be redundant in the -160 Tdc promoter and to reside between -99 and -37 and between -37 and + 198.

Alkaloids↗
PubMed1979

Induction of oestrus and fertility in the anoestrous ewe with hormones and controlled lighting and temperature.

A programme consisting of 14 daily injections of progesterone (10 mg) followed by single injection of PMSG (500 i.u.) and oestradiol- 17 beta (30 micrograms), along with controlled temperature (18-20 degrees C) and lighting (10 h light/24 h), was applied to 60 anoestrous ewes between late May and early August to induce reproductive activity. Breeding started within 24 h of the oestradiol injection and 80.0% of the ewes conceived at the induced oestrus. Dorset ewes had higher conception (95.2 versus 71.8%) and prolificacy (1.74 versus 1.52 fetuses/ewe) rates than did crossbred Suffolk ewes. Plasma progesterone concentrations during progesterone administration were significantly higher than those found during anoestrus and were generally lower in ewes which did not conceive than in those which did. The plasma progesterone data indicated that ovulation had occurred in most of the ewes which were not pregnant at 90-100 days and that many may have been pregnant initially but then lost the conceptus.

Animals↗
PubMed1987

Induction of antiphosphocholine antibodies utilizing lambda light chains in BALB/c mice.

BALB/c mice immunized with 1 or 100 micrograms of phosphocholine (PC)-keyhole-limpet hemocyanin absorbed on aluminum hydroxide gel (alum) produced up to 50% lambda 1-light-chain-containing anti-PC antibodies in their serum. Only 10% lambda 1 antibodies were seen when complete Freund's adjuvant or bentonite were used as the adjuvant or if PC-bovine serum albumin was used with alum. Thus, the induction of large lambda-antibody responses to PC (a response usually dominated by kappa-antibodies) was both adjuvant- and carrier-dependent.

Adjuvants, Immunologic↗
PubMed2001

Serotonin, excitatory amino acids and the photic control of melatonin rhythms and SCN c-FOS in the rat.

There is a growing acceptance that serotonergic pathways to the suprachiasmatic nucleus play an important role in the mediation and modulation of light entrainment of rhythms. In this study administration of the 5-HT(2A/2C) agonist (+/-)-1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane (DOI, 0.5 mg/kg) at mid dark caused a phase shift in the onset of the urinary excretion of 6-sulphatoxymelatonin in rats that was sustained for at least 8 days and was blocked by the specific 5-HT(2C) antagonist SB-242084. Administration of DOI (2 mg/kg) across the night resulted in the appearance of c-FOS in the nucleus of cells in the suprachiasmatic nucleus during subjective darkness, but did not cause induction at the time of expected lights on (CT0). By contrast light exposure induced c-fos throughout the night including CT0. Administration of the NMDA receptor antagonist MK-801 (3 mg/kg) prior to light pulses had no effect on c-fos in the first part of the night, but towards the expected time of lights on, became progressively more potent, such that by CT0, light induction of c-fos was almost completely inhibited. These results provide further evidence that serotonin plays a role in the mediation of light effects on rhythms in the rat.

Animals↗
PubMed2004

High-dose melphalan with autologous stem cell transplantation after VAD induction chemotherapy for treatment of amyloid light chain amyloidosis: a single centre prospective phase II study.

Amyloid light chain (AL) amyloidosis is the result of a clonal plasma cell expansion, in which monoclonal light chains transform to amyloid deposit in various tissues and can lead to organ dysfunction and organ failure. The median survival of patients with AL amyloidosis without therapy is 10-14 months. With high-dose melphalan (HDM) and autologous stem cell transplantation (ASCT), haematological and clinical remission rates of up to 50% of treated patients have been reported from phase II studies. HDM followed by ASCT appears to prolong survival in patients, if haematological remission can be reached. In this phase II study, we evaluated vincristine, adriamycin and dexamethasone (VAD) as induction chemotherapy prior to stem cell mobilization and HDM with ASCT. The regimen was, in general, feasible in patients with AL amyloidosis, but VAD chemotherapy had a considerable World Health Organization (WHO) grade III-IV toxicity (25%) and mortality (7%) rate. VAD pretreatment did not interfere with stem cell mobilization and HDM with ASCT was possible in 86% of patients. The overall treatment efficacy was comparable with reported results of HDM and ASCT without preceding chemotherapy. We could not show an additional benefit of VAD induction in terms of increasing haematological response rate; however the 13% mortality rate after HDM and ASCT in our series was lower than the previous report.

Adult↗
PubMed2005

ELF4 is a phytochrome-regulated component of a negative-feedback loop involving the central oscillator components CCA1 and LHY.

Evidence has been presented that a negative transcriptional feedback loop formed by the genes CIRCADIAN CLOCK ASSOCIATED (CCA1), LATE ELONGATED HYPOCOTYL (LHY) and TIMING OF CAB (TOC1) constitutes the core of the central oscillator of the circadian clock in Arabidopsis. Here we show that these genes are expressed at constant, basal levels in dark-grown seedlings. Transfer to constant red light (Rc) rapidly induces a biphasic pattern of CCA1 and LHY expression, and a reciprocal TOC1 expression pattern over the first 24 h, consistent with initial induction of this synchronous oscillation by the light signal. We have used this assay with wild-type and mutant seedlings to examine the role of these oscillator components, and to determine the function of ELF3 and ELF4 in their light-regulated expression. The data show that whereas TOC1 is necessary for light-induced CCA1/LHY expression, the combined absence of CCA1 and LHY has little effect on the pattern of light-induced TOC1 expression, indicating that the negative regulatory arm of the proposed oscillator is not fully functional during initial seedling de-etiolation. By contrast, ELF4 is necessary for light-induced expression of both CCA1 and LHY, and conversely, CCA1 and LHY act negatively on light-induced ELF4 expression. Together with the observation that the temporal light-induced expression profile of ELF4 is counter-phased to that of CCA1 and LHY and parallels that of TOC1, these data are consistent with a previously unrecognized negative-feedback loop formed by CCA1/LHY and ELF4 in a manner analogous to the proposed CCA1/LHY/TOC1 oscillator. ELF3 is also necessary for light-induced CCA1/LHY expression, but it is neither light-induced nor clock-regulated during de-etiolation. Taken together, the data suggest (a) that ELF3, ELF4, and TOC1 all function in the primary, phytochrome-mediated light-input pathway to the circadian oscillator in Arabidopsis; and (b) that this oscillator consists of two or more interlocking transcriptional feedback loops that may be differentially operative during initial light induction and under steady-state circadian conditions in entrained green plants.

Arabidopsis↗
PubMed1978

Induction of persistent estrus by constant light: effects of neonatal constant light and Harderian gland function.

The effect of constant light on the age at onset of persistent estrus was compared in rats exposed to constant light since birth (LL-0) and those exposed beginning at 70 days of age (LL-70). Persistent estrus occurred about 27 days later in the LL-0 rats than in the LL-70 rats. Exposure to LL for just the 1st 15 days of life (LL-0-15) and then subsequent exposure to LL at 71 days also delayed the induction of persistent estrus. Neonatal injection of a Harderian gland (HG) homogenate to LL-0-15 rats reduced the age of vaginal opening and 1st estrus and reduced the delayed onset of persistent estrus caused by the neonatal LL. Harderianectomy of LL-0 or hematoporphyrin injections in LL-0-15 rats had no effect on the onset of LL-induced persistent estrus.

Animals↗