SEARCH · PubMed Health

Results for “light induction”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 829 records · Page 46Linked to original sources

PubMed2004

Factors affecting somatic embryogenesis in Prunus incisa cv. February Pink.

Factors affecting somatic embryogenesis from root explants of Prunus incisa Thunb. cv. February Pink were investigated. Using a medium containing Murashige and Skoog salts and vitamins supplemented with 10 microM 2,4-dichlorophenoxyacetic (2,4-D), we evaluated the effects of light, growth regulators, amino acids, carbohydrate source, and root induction medium. Explants cultured under light or dark conditions both resulted in the formation of embryos. Embryogenesis was inhibited by the addition of 6-benzyladenine, thidiazuron, or gibberellic acid to the medium. Amino acids were not effective in promoting embryogenesis, with high levels of amino acids actually inhibiting it. Sucrose and glucose effectively induced embryogenesis, while sorbitol and mannitol completely inhibited it. Sucrose and glucose also promoted secondary embryogenesis. Embryos that formed in medium containing 4% or 5% sucrose were abnormally shaped and did not fully develop, while those that formed in medium with sucrose concentrations of 2% or 3% were much more vigorous. Root explants that were induced on medium containing 1.0 micro M indole-3-butyric acid (IBA) produced more somatic embryos than explants induced on medium without IBA. Approximately 50% of the roots induced on medium containing 1.0 microM IBA produced somatic embryos on medium containing 10 microM 2,4-D and 3% sucrose.

Amino Acids↗

PubMed2006

Effect of light on seed germination of eight wetland Carex species.

BACKGROUND AND AIMS: In wetland plant communities, species-specific responses to pulses of white light and to red : far-red light ratios can vary widely and influence plant emergence from the seed bank. Carex species are the characteristic plants of sedge meadows of natural prairie wetlands in mid-continental USA but are not returning to restored wetlands. Little is known about how light affects seed germination in these species-information which is necessary to predict seed bank emergence and to develop optimal revegetation practices. The effects of light on germination in eight Carex species from prairie wetlands were investigated. METHODS: Non-dormant seeds of eight Carex species were used to determine the influence of light on germination by examining: (a) the ability of Carex seeds to germinate in the dark; (b) the effect of different lengths of exposures to white light on germination; (c) whether the effect of white light can be replaced by red light; and (d) whether the germination response of Carex seeds to white or red light is photoreversible by far-red light. KEY RESULTS: Seeds of C. brevior and C. stipata germinated >25 % in continuous darkness. Germination responses after exposure to different lengths of white light varied widely across the eight species. Carex brevior required <15 min of white light for > or =50 % germination, while C. hystericina, C. comosa, C. granularis and C. vulpinoidea required > or =8 h. The effect of white light was replaced by red light in all species. The induction of germination after exposure to white or red light was reversed by far-red light in all species, except C. stipata. CONCLUSIONS: The species-specific responses to simulated field light conditions suggest that (a) the light requirements for germination contribute to the formation of persistent seed banks in these species and (b) in revegetation efforts, timing seed sowing to plant community development and avoiding cover crops will improve Carex seed germination.

Carex Plant↗

PubMed1996

Effects of ultraviolet light in vascular cells in vitro and in intact atherosclerotic explants: potential role of apoptosis in vascular biology.

Complex cell-to-cell interactions are known to participate during vascular injury and remodeling, resulting in smooth muscle cell proliferation. Mechanical interventions have yielded little benefit in limiting this process and several site-specific genetic therapies are not yet clinically available. The aim of this study was to delineate the effect of very short wavelength ultraviolet (UVC) light therapy on the viability of macrophage and smooth muscle cells. Vascular cells were both treated in vitro and in intact explanted atherosclerotic aortic segments ex vivo with UVC light. Brief exposure to short wavelength UVC light in the absence of photosensitizers elicited a differential temporal and functional response among treated cells. However, dramatic reduction in both cellular viability and proliferative capacity with eventual cell demise was observed in all UVC-treated cells. Flow cytometry and immunohistochemical analyses revealed the presence of extensive DNA fragmentation, suggestive of apoptosis as a predominant pathway of cell death in these cells exposed to UVC light. We hypothesize that selective induction of apoptosis, in contrast to necrosis, with UVC light may represent a beneficial approach to interdict the complex biologic cascade of messengers that participate in the restenotic response to vascular injury.

Animals↗

PubMed2001

Light-dependent gene expression for proteins in the respiratory chain of potato leaves.

Expression of genes for respiratory chain dehydrogenases was investigated in potato (Solanum tuberosum L. cv. Desiree) leaves. The recently characterized nda1 and ndb1 genes, homologues to genes encoding the non-proton pumping respiratory chain NADH-dehydrogenases of Escherichia coli and yeast, were compared to genes encoding catalytic subunits of the proton-pumping NADH dehydrogenase (complex I). As leaves develop from young to mature, the nda1 transcript level increases, accompanied by an elevation in immunodetected NDA protein and internal rotenone-insensitive NADH oxidation. The other investigated transcripts, proteins and NAD(P)H oxidation activities were essentially unchanged. A variation in transcript level, specific for nda1, is seen at different times of the day with highest expression in the morning. This variation also influences the apparent developmental induction. Further, the nda1 mRNA in leaves specifically and completely disappears during dark treatment, with a rapid re-induction when plants are returned to light. Corresponding immunodetected NDA protein is specifically decreased in mitochondria isolated from dark-treated plants, accompanied by a lower capacity for internal rotenone-insensitive NADH oxidation. Complete light dependence and diurnal changes in expression have previously not been reported for genes encoding respiratory chain proteins. Qualitatively similar to NDA, the alternative oxidase showed developmental induction and light dependence. In addition to the specific change in nda1, a general, slower down-regulation in darkness was seen for the other NAD(P)H dehydrogenase genes. The nda1 expression during development, and in response to light, indicates a specific role of the encoded enzyme in the photosynthetically associated mitochondrial metabolism.

Aging↗

PubMed1989

Characterization of phytochrome-regulated gene expression in a photoautotrophic cell suspension: possible role for calmodulin.

A photoautotrophic suspension culture of soybeans was found to exhibit light-dependent expression of the genes encoding the major chlorophyll a- and b-binding protein (CAB). The expression was mediated by phytochrome, since it was induced by red light and reversed by far-red light. The maximal level as well as the kinetics of the induction were comparable between the suspension culture and soybean seedlings. Using this cell culture, we addressed the question of whether a calcium- and/or calmodulin-mediated step is involved in the signal transduction process between phytochrome and CAB expression. We found that W-7, a potent calmodulin antagonist, severely attenuated the induction of CAB mRNA by light, whereas W-5, a weak calmodulin antagonist, had little effect. Control experiments demonstrated that W-7 treatment did not block the induction of hsp-75 by heat shock. The addition of ionomycin, a calcium ionophore, induced a low level of CAB mRNA accumulation in the dark which could be further enhanced by light treatment. We propose that calmodulin activation by light is necessary but not sufficient to induce maximal CAB expression.

Calcium↗

PubMed2003

Role for antisense RNA in regulating circadian clock function in Neurospora crassa.

The prevalence of antisense RNA in eukaryotes is not known and only a few naturally occurring antisense transcripts have been assigned a function. However, the recent identification of a large number of putative antisense transcripts strengthens the view that antisense RNAs might affect a wider variety of processes than previously thought. Here we show that in the model organism Neurospora crassa entrainment of the circadian clock, which is critical for the correct temporal expression of genes and their products, is controlled partly by an antisense RNA arising from a clock component locus. In a wild-type strain, levels of antisense frequency (frq) transcripts cycle in antiphase to sense frq transcripts in the dark, and are inducible by light. In mutant strains in which the induction of antisense frq RNA by light is abolished, the time of the internal clock is delayed relative to the wild-type strain, and resetting of the clock by light is altered. These data provide an unexpected link between antisense RNA and circadian timing and provide a new example of a eukaryotic cellular process regulated by naturally occurring antisense RNA.

Circadian Rhythm↗

PubMed1988

Calcium in the regulation of gravitropism by light.

The red light requirement for positive gravitropism in roots of corn (Zea mays cv "Merit") provides an entry for examining the participation of calcium in gravitropism. Applications of calcium chelators inhibit the light response. Calcium channel blockers (verapamil, lanthanum) can also inhibit the light response, and a calcium ionophore, A23187, can substitute for light. One can substitute for red light by treatments which have elsewhere been shown to trigger Ca2+ influx into the cytosol, e.g. heat or cold shock. Agents which are known to be agonists of the phosphatidylinositol second messenger system (serotonin, 2,4-dichlorophenoxyacetic acid, deoxycholate) can each partially substitute for the red light, and Li+ can inhibit the light effect. These experiments suggest that the induction of positive gravitropism by red light involves a rise in cytoplasmic Ca2+ concentration, and that a contribution to this end may be made by the phosphatidylinositol second messenger system.

Calcimycin↗

PubMed1983

[Effect of light on the development of Saccobolus platensis].

The ascomycetous fungi Saccobolus platensis requires light for apothecial production. Photoinduction could be accomplished by continuous light and also by minor light periods. When apothecia were photoinduced by single 24 hour photoperiods, the effect varied according to the stage of development of the mycelium: it was most photoreceptive at the 5th day of growth. At this stage a single 6 hour irradiation was enough to induce 50% fructifications of the control (continuous light). After photoinduction, protoapothecia reached maturity independently of light treatment. Light quality influenced both apothecial number and size. Near ultraviolet light was the most effective for the induction of apothecia, followed by blue light; the maximum apothecial size was reached under blue light.

Ascomycota↗

PubMed2001

External Ca(2+) is essential for chloroplast movement induced by mechanical stimulation but not by light stimulation.

In the fern Adiantum capillus-veneris, chloroplast movement is induced by mechanical stimulation as well as by light stimulation. Directional movement of both types depends on an actin-based motile system. To investigate the physiological relationship between mechanical and light signaling in the regulation of chloroplast movement, we examined the mechano-response of chloroplasts whose motility had been already restricted after photo-relocation. Chloroplast mechano-avoidance movement was induced under all of the photo-relocation conditions tested, indicating that mechano-specific signals generated by mechanical stimulation dominate over the light signals and reactivate the motility of chloroplasts. When the effects of external Ca(2+) on the induction of mechano- and light responses were examined, strikingly different requirements of external Ca(2+) were found for each. In medium without Ca(2+), the mechano-response was suppressed but no effects were observed on photo-response. Mechano-relocation movement of chloroplasts was inhibited by 100 microM lanthanum (La(3+)), a plasma membrane calcium channel blocker, and by 10 microM gadolinium (Gd(3+)), a stretch-activated channel blocker. However, the same concentrations of these drugs did not affect the photo-relocation movement at all. These results suggest that the influx of external Ca(2+) is crucial for the early signaling step of chloroplast mechano-relocation but not for that of photo-relocation. This is the first report showing the separation of signaling pathways in mechano- and photo-relocation of chloroplasts.

Actins↗

PubMed1967

Effects of continuous light on the reproductive cycle of the female rat: induction of ovulation and pituitary gonadotrophins during persistent oestrus.

Explore the source record for details and available documents.

Animals↗

PubMed1994

The LOX1 Gene of Arabidopsis Is Temporally and Spatially Regulated in Germinating Seedlings.

We examined the temporal and spatial expression patterns of the LOX1 gene during the development of Arabidopsis thaliana seedlings. Measurements of steady-state LOX1 mRNA levels indicated that this gene is transiently expressed during germination. LOX1 mRNA was not detected in seed that had imbibed (T0) but reached a maximum level by 1 d in both light- and dark-grown seedlings. The induction of the LOX1 gene was not light dependent; however, mRNA levels were 4-fold greater in light-grown seedlings. Immunoblot analysis of lipoxygenase protein levels and measurements of enzyme activity suggested that the induction of the LOX1 gene resulted in the production of functional lipoxygenase enzyme. Lipoxygenase protein was not present in dry seed or seed that had imbibed, but was first detected by immunoblot analysis after 1 and 2 d of growth in the light and dark, respectively. In both cases, lipoxygenase protein levels remained high for 2 d and then declined. Lipoxygenase activity paralleled the changes in protein levels. In situ hybridization studies revealed that the LOX1 gene is transiently expressed in the epidermis and the aleurone layer during germination. LOX1 mRNA levels were particularly high in the epidermis of the radicle and the adaxial side of the cotyledons. These results suggest that the LOX1 gene product is produced specifically during early germination and plays a role in the functioning of the epidermis.

Journal Article↗

PubMed1982

Differential reactivation of zinc-mediated metallothionein induction in ultraviolet-irradiated normal and repair-deficient human cells.

The ubiquitous, low-molecular-weight, thiol-rich, metal-binding protein, metallothionein (MT), can be induced in cultured normal human fibroblasts (NF) and xeroderma pigmentosum (XP) cells by exposure to ZnCl2. Both NF and XP cells tolerate up to 200 microM ZnCl2 in the growth medium, upon addition of ZnCl2 (200 microM) to monolayer cultures, both NF and XP cells showed similar kinetics for the induction of MT synthesis: Within 7 hours the MT synthesis rate rose from a low, marginally detectable rate to a maximal rate at least 50-fold greater than the basal rate. The induction of MT synthesis in both cell types was inhibited by actinomycin D (5 microgram/ml), indicating that the induction process is controlled at the level of transcription. Exposure of NF and XP cells to far ultraviolet light (UV) followed by induction with ZnCl2 resulted in a UV dose-dependent decrease in the he maximal rate of MT synthesis measured 8.5 hours postirradiation. The UV sensitivity of the MT induction was greater in XP cells than in NF cells. However, considerations of the differential repair capacities of NF and XP cells superimposed upon the kinetics of MT induction were invoked to explain the apparent differential UV sensitivity of MT induction. Liquid holding recovery experiments showed that NF cells possess the capacity to reactivate this inducible gene function rapidly while XP cells are deficient in the reactivation capacity. These results are discussed in the context of both UV transcriptional mapping of this inducible gene function and development of techniques for measuring repair of transcription-blocking lesions.

Cells, Cultured↗

PubMed1981

Effect of psoralen-induced photodermatitis on tryptophan metabolism in rats.

Tryptophan metabolism 'via kynurenine' has been studied in rats before and after induction of experimental light-conditioned dermatitis with psoralen. Tryptophan load in animals during the acute phase of dermatitis (one day after induction) causes a markedly increased urinary excretion of total metabolites in comparison with that obtained before dermatitis. During this phase of the skin disease tryptophan pyrrolase activity is significantly increased and kynureninase activity significantly decreased in liver in respect to the control animals. Kynurenine aminotransferase activity shows no significant variations in both liver and kidneys. After 6 days of dermatitis, when the skin damage is in repair, both the excretory values of the urinary metabolites after L-tryptophan load and the enzymic activities are similar to those before dermatitis.

Animals↗

PubMed1979

Tryptophan metabolism in animals with dermatitis. I) In Rats.

Tryptophan metabolism "via kynurenine" after load of amino-acid has been studied in urine of rats before and after induction of experimental light-conditioned dermatitis with psoralen. Tryptophan load in animals during the acute phase of dermatitis (one day after induction) causes a markedly increased urinary excretion of total metabolites in comparison with that obtained before dermatitis. After six days of dermatitis, when the skin damage was in repair, the excretory values after tryptophan load in rats are only slightly increased indicating that the metabolic disturbance is correlated with the skin damage.

Animals↗

PubMed2003

Growth suppression, altered stomatal responses, and augmented induction of heat shock proteins in cytosolic ascorbate peroxidase (Apx1)-deficient Arabidopsis plants.

The accumulation of hydrogen peroxide (H2O2) in plants is typically associated with biotic or abiotic stresses. However, H2O2 is continuously produced in cells during normal metabolism. Yet, little is known about how H2O2 accumulation will affect plant metabolism in the absence of pathogens or abiotic stress. Here, we report that a deficiency in the H2O2-scavenging enzyme, cytosolic ascorbate peroxidase (APX1), results in the accumulation of H2O2 in Arabidopsis plants grown under optimal conditions. Knockout-Apx1 plants were characterized by suppressed growth and development, altered stomatal responses, and augmented induction of heat shock proteins during light stress. The inactivation of Apx1 resulted in the induction of several transcripts encoding signal transduction proteins. These were not previously linked to H2O2 signaling during stress and may belong to a signal transduction pathway specifically involved in H2O2 sensing during normal metabolism. Surprisingly, the expression of transcripts encoding H2O2 scavenging enzymes, such as catalase or glutathione peroxidase, was not elevated in knockout-Apx1 plants. The expression of catalase, two typical plant peroxidases, and several different heat shock proteins was however elevated in knockout-Apx1 plants during light stress. Our results demonstrate that in planta accumulation of H2O2 can suppress plant growth and development, interfere with different physiological processes, and enhance the response of plants to abiotic stress conditions. Our findings also suggest that at least part of the induction of heat shock proteins during light stress in Arabidopsis is mediated by H2O2 that is scavenged by APX1.

Arabidopsis↗

PubMed1993

Studies on the constancy of the blue and green fluorescence yield during the chlorophyll fluorescence induction kinetics (Kautsky effect).

Blue (F450) and green (F530) leaf fluorescence were studied together with the red chlorophyll fluorescence (emission maxima F690 and F735) during light-induced chlorophyll fluorescence induction kinetics (Kautsky effect) in predarkened leaves of wheat (Triticum aestivum L.) and soybean (Glycine max L.). The intensity of the red chlorophyll fluorescence decreased from maximum fluorescence Fm to steady-state fluorescence Fs, and the fluorescence ratio F690/F735 decreased by about 10% from Fm to Fs. However, blue and green fluorescence intensities remained constant throughout the measuring time. Consequently, the ratio of blue to red fluorescence (F450/F690) increased during chlorophyll fluorescence induction kinetics, whereas the ratio of blue to green fluorescence (F450/F530) remained unchanged within the same period. The knowledge of these ratios will be a prerequisite for the interpretation of remote sensing data from terrestrial vegetation.

Chlorophyll↗

PubMed2004

Reverse gyrase recruitment to DNA after UV light irradiation in Sulfolobus solfataricus.

Induction of DNA damage triggers a complex biological response concerning not only repair systems but also virtually every cell function. DNA topoisomerases regulate the level of DNA supercoiling in all DNA transactions. Reverse gyrase is a peculiar DNA topoisomerase, specific to hyperthermophilic microorganisms, which contains a helicase and a topoisomerase IA domain that has the unique ability to introduce positive supercoiling into DNA molecules. We show here that reverse gyrase of the archaean Sulfolobus solfataricus is mobilized to DNA in vivo after UV irradiation. The enzyme, either purified or in cell extracts, forms stable covalent complexes with UV-damaged DNA in vitro. We also show that the reverse gyrase translocation to DNA in vivo and the stabilization of covalent complexes in vitro are specific effects of UV light irradiation and do not occur with the intercalating agent actinomycin D. Our results suggest that reverse gyrase might participate, directly or indirectly, in the cell response to UV light-induced DNA damage. This is the first direct evidence of the recruitment of a topoisomerase IA enzyme to DNA after the induction of DNA damage. The interaction between helicase and topoisomerase activities has been previously proposed to facilitate aspects of DNA replication or recombination in both Bacteria and Eukarya. Our results suggest a general role of the association of such activities in maintaining genome integrity and a mutual effect of DNA topology and repair.

DNA Damage↗

PubMed1996

The expression of the Acinetobacter calcoaceticus recA gene increases in response to DNA damage independently of RecA and of development of competence for natural transformation.

Using the lacZ operon fusion technique, the transcriptional control of the Acinetobacter calcoaceticus recA gene was studied. A low (approximately twofold) inductive capacity was observed for compounds that damage DNA and/or inhibit DNA replication, e.g. methyl methanesulfonate, mitomycin C, UV light and nalidixic acid. Induction of the recA gene by DNA damage was independent of functional RecA. The presence of the recA promoter region on a multicopy plasmid had the same effect on recA transcription as the presence of DNA-damaging agents. Thus, recA expression in A. calcoaceticus appears to be regulated in a novel fashion, possibly involving a non-LexA-like repressor. Regulation of the recA gene in A. calcoaceticus appears not to be part of a regulon responsible for competence for natural transformation: in cells exhibiting extremely low transformation frequencies, the level of transcription of the recA gene was found to be comparable to the level found in cells in the state of maximal competence.

Acinetobacter calcoaceticus↗