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At least 865 records · Page 48Linked to original sources
PubMed1990

The polyamines of Xanthium strumarium and their response to photoperiod.

Flowering plants of Xanthium strumarium L., grown in 8 h photoperiods, were analysed for polyamines. Putrescine, spermidine and spermine were found throughout the plant in three forms: (a) as free polyamines; (b) conjugates soluble in 5% trichloracetic acid (TCA); and (c) bound to the TCA-insoluble precipitate. On a fresh weight basis, total polyamines are most abundant in young leaves and buds, especially flower buds. Spermidine predominates in the free polyamine fractions, while spermine is dominant in the conjugated fraction. Transfer of vegetative plants from 16 h photoperiods to 1, 2, 3, or 4 inductive cycles (8 h light + 16 h uninterrupted dark) caused rapid and marked changes in the polyamine titer of the leaves and ultimately, floral initiation. The titer of free putrescine per mg protein declined progressively with induction in all leaf sizes, while the titers of free spermidine and spermine rose during days 2 and 3 in small and expanding leaves. Conjugated putrescine, spermidine and spermine rose sharply after only 1 inductive cycle, especially in small and expanding leaves, and maintained the higher level for at least several cycles. In plants given 4 inductive cycles, buds harvested after 4 additional days had sharply elevated levels of conjugated polyamines, especially spermine, on a protein basis.

Light↗
PubMed1997

DNA repair of UV photoproducts and mutagenesis in human mitochondrial DNA.

The induction and repair of DNA photolesions and mutations in the mitochondrial (mt) DNA of human cells in culture were analysed after cell exposure to UV-C light. The level of induction of cyclobutane pyrimidine dimers (CPD) in mitochondrial and nuclear DNA was comparable, while a higher frequency of pyrimidine (6-4) pyrimidone photoproducts (6-4 PP) was detected in mitochondrial than in nuclear DNA. Besides the known defect in CPD removal, mitochondria were shown to be deficient also in the excision of 6-4 PP. The effects of repair-defective conditions for the two major UV photolesions on mutagenesis was assessed by analysing the frequency and spectrum of spontaneous and UV-induced mutations by restriction site mutation (RSM) method in a restriction endonuclease site, NciI (5'CCCGG3') located within the coding sequence of the mitochondrial gene for tRNALeu. The spontaneous mutation frequency and spectrum at the NciI site of mitochondrial DNA was very similar to the RSM background mutation frequency (approximately 10(-5)) and type (predominantly GC>AT transitions at G1 of the NciI site). Conversely, an approximately tenfold increase over background mutation frequency was recorded after cell exposure to 20 J/m2. In this case, the majority of mutations were C>T transitions preferentially located on the non-transcribed DNA strand at C1 and C2 of the NciI site. This mutation spectrum is expected by UV mutagenesis. This is the first evidence of induction of mutations in mitochondrial DNA by treatment of human cells with a carcinogen.

Base Sequence↗
PubMed1999

A role for cyclic AMP in entrainment of the circadian oscillator in Xenopus retinal photoreceptors by dopamine but not by light.

The circadian oscillator in Xenopus retinal photoreceptor layers can be reset in similar ways by light and agonists of D2-like dopamine receptors. Treatments that increase cyclic AMP levels act on this oscillator in an opposite fashion, mimicking darkness in the induction of phase shifts. Light and dopamine have each been reported to inhibit adenylate cyclase in photoreceptors. Together, these data suggest that the transduction pathways for entrainment by dopamine and/or light include suppression of cyclic AMP or a cyclic AMP-sensitive step. In these studies, we examined this hypothesis by measuring the effects of treatment with a cyclic AMP analogue on the phase shifts induced in photoreceptor melatonin rhythms by light or a D2 receptor agonist (quinpirole). When photoreceptor layers were treated simultaneously with 8-(4-chlorophenylthio)cyclic AMP (8-CPT-cAMP) and quinpirole at any of three different phases of the circadian cycle, the resulting phase shifts of the melatonin rhythm were always the same as those caused by 8-CPT-cAMP alone. This indicates that there is a cyclic AMP-sensitive step in the dopamine entrainment pathway. In contrast, light pulses did reset the oscillator in the presence of elevated cyclic AMP. This suggests a separate cyclic AMP-insensitive transduction pathway for entrainment by light. Quinpirole reduced basal levels of cyclic AMP in photoreceptors, but light did not. These data suggest that cyclic AMP plays a role in the entrainment pathway activated by dopamine but not in the entrainment pathway activated by light.

Animals↗
PubMed2003

Optimization of biomass, total carotenoids and astaxanthin production in Haematococcus pluvialis Flotow strain Steptoe (Nevada, USA) under laboratory conditions.

The microalga Haematococcus pluvialis Flotow is one of the natural sources of astaxanthin, a pigment widely used in salmon feed. This study was made to discover optimal conditions for biomass and astaxanthin production in H. pluvialis from Steptoe, Nevada (USA), cultured in batch mode. Growth was carried out under autotrophic (with NaNO3, NH4Cl and urea) and mixotrophic conditions (with 4, 8, 12 mM sodium acetate) under two photon flux densities (PFD) (35 and 85 mumol m-2 s-1). The carotenogenesis was induced by 1) addition of NaCl (0.2 and 0.8%), 2) N-deprivation and 3) high PFD (150 mumol m-2 s-1). Total carotenoids were estimated by spectrophotometry and total astaxanthin by HPLC. Ammonium chloride was the best N-source for growth (k = 0.7 div day-1, 228-258 mg l-1 and 2.0 x 10(5)-2.5 x 10(5) cells ml-1 at both PFD, respectively). With increasing acetate concentration, a slight increment in growth occurred only at 85 mumol m-2 s-1. Light was the best inductive carotenogenic factor, and the highest carotenoid production (4.9 mg l-1, 25.0 pg cell-1) was obtained in cultures pre-grown in nitrate at low light. The NaCl caused an increase in carotenoid content per cell at increasing salt concentrations, but resulted in a high cell mortality and did not produce any increment in carotenoid content per volume compared to cultures grown at 150 mumol m-2 s-1. The highest carotenoid content per cell (22 pg) and astaxanthin content per dry weight (10.3 mg g-1) (1% w/w) were obtained at 85 mumol m-2 s-1 with 0.8% NaCl.

Biomass↗
PubMed1987

Drug-induced penile erections in rats: indications of serotonin1B receptor mediation.

The induction of penile erections by a variety of compounds with a direct or indirect effect on serotonin (5HT) receptors was investigated in rats. L-5-Hydroxy-tryptophan (L-5HTP) induced penile erections when co-administered with nialamide and the peripheral decarboxylase inhibitor benserazide, indicating that the site of action for inducing penile erections is within the central nervous system. Penile erections were also induced by the 5HT uptake inhibitors zimelidine, fluoxetine, citalopram, Org 6997, by the 5HT-releasing agent fenfluramine and by the putative 5-HT1B receptor agonist 1-(3'-chlorophenyl)-piperazine (mCPP). The 5HT1A-agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) did not induce penile erections. The less selective 5HT receptor agonists 5-methoxy-N,N-dimethyl-tryptamine (5MeODMT), 5-methoxytryptamine (5MeOT), dl-lysergic acid diethylamide (LSD) and Ru 24969 were also ineffective. Induction of penile erections by quipazine appeared only when this compound was co-administered with the 5HT2 receptor antagonist pirenperone. Receptor antagonists were tested against penile erections induced by Org 6997. The beta-adrenoceptor antagonists that also have 5HT1 antagonistic properties, (S)-pindolol and dl-propranolol, antagonized Org 6997-induced penile erections but butoxamine and metoprolol did not. Spiperone and pirenperone in doses selective for 5HT1A and 5HT2 receptors respectively were also inactive. Haloperidol, 0.46 mg/kg, partially attenuated penile erections induction. The data are discussed in the light of the hypothesis that penile erections induction by serotonin-mimetic compounds is mediated by 5HT1B receptors in the striatum.

5-Hydroxytryptophan↗
PubMed1996

Immediate early gene expression in cat visual cortex during and after the critical period: differences between EGR-1 and Fos proteins.

Immediate early gene (IEG) expression in the cat visual cortex is highly responsive to visual input and may initiate genetic mechanisms responsible for neuronal plasticity. The present study used immunohistochemical methods to address two issues regarding IEG expression in response to visual input. One was to define the differential response of distinct IEG families by comparing EGR-1 (also termed zif-268, NGFI-A, and Krox-24) and Fos proteins. The second was to determine whether IEG expression, in addition to reflecting neural activity, is related to the state of plasticity by comparing young and adult visual cortex. Immunoreactivity of the two IEG proteins was compared between 5-week-old and adult cats under three conditions of visual input: ambient light to assess basal levels of expression, 1 week of darkness to assess the effect of reduced activity, and exposure to light after 1 week of darkness to determine rapid changes in expression as a result of visual input. At both ages, there were marked differences in the expression of the two IEG proteins. EGR-1 responded to visual input with sustained changes in its level of expression. It showed high basal levels, reduced expression in darkness, and a rapid return to high constitutive levels with the introduction of light. Fos showed a markedly different profile. It had very low basal expression which was not demonstrably affected by darkness and its principal response was a marked transient induction upon exposure to light after darkness. These unique changes in expression highlight the complex response across IEGs to environmental input and suggest a genetic "on/off' signaling mechanism. There were marked differences in the laminar distribution of EGR-1 and Fos proteins between young and adult cats. In young animals, cells in all visual cortical layers showed high levels of EGR-1 and Fos proteins. In adults, immunostaining was largely specific to cells located above and below layer IV and only very faint labeling occurred within layer IV. These differences in laminar distribution between ages are inconsistent with a simple explanation of IEG expression in terms of neural activity level; rather, they suggest a relation between IEG expression and the state of plasticity in visual cortex.

Animals↗
PubMed2004

Two independent light signals cooperate in the activation of the plastid psbD blue light-responsive promoter in Arabidopsis.

The psbD blue light-responsive promoter (BLRP), whose activation has been considered to require strong blue light, is recognized only by SIG5 among six sigma factors of plastid RNA polymerase in Arabidopsis. We found SIG5 transcript accumulation was rapidly induced after a 30-min induction time by blue light (470 nm) with an intensity threshold of 5 micromol m(-2)s(-1) through cryptochromes. Besides this weak blue light, the psbD BLRP activation required the stronger light such as 50 micromol m(-2)s(-1) irrespective of blue or red light (660 nm). Thus, the two independent light signalings, the cryptochrome-mediated signaling to induce SIG5 transcription and the stronger light-dependent signaling, cooperate to activate the psbD BLRP.

Arabidopsis↗
PubMed1998

[HPETE, an arachidonic acid metabolite, induces apoptosis in rat retina in vitro].

BACKGROUND: Apoptosis is a gene-regulated mode of cell death which gains increasing importance in retinal pathologies such as retinitis pigmentosa, retinal detachment and proliferative vitreoretinopathy. A better understanding of the regulation of apoptosis could imply the means to reduce photoreceptor cell death and thereby provide therapeutic strategies to influence the time course of retinal diseases. Previous studies in our laboratory demonstrated that light induces apoptosis in the rat retina in vivo as a function of light dose. In several cell systems, oxidative stress including oxygenated metabolites of arachidonic acid (AA) was found to evoke apoptosis. We have observed a light-elicited release of AA and the subsequent formation of its metabolites in the rat retina. Therefore, AA and its metabolites appeared to be suitable candidates for the induction of apoptosis during light exposure. MATERIALS AND METHODS: Isolated rat retinas were incubated for 60, 120 and 180 min, respectively, with and without the addition of 30 mumol 5S-hydroperoxyeicosatetraenoic acid (5-HPETE). Retinas were then processed for light- and electron microscopy and examined for the morphological signs of apoptosis. The rate of apoptosis in the outer nuclear layer was assessed quantitatively. RESULTS: 5S-HPETE induces apoptosis of photoreceptors in the rat retina in vitro. Quantitative analysis revealed a significant increase in the rate of apoptosis of 5S-HPETE-treated retinas when compared to untreated controls. CONCLUSION: Arachidonic acid metabolites released upon light exposure may represent messenger candidates for apoptosis in the retina.

Animals↗
PubMed2001

Functional elements of the strong psbAI promoter of Synechococcus elongatus PCC 7942.

The psbAI gene of the cyanobacterium Synechococcus elongatus PCC 7942 is one of three psbA genes that encode a critical photosystem II reaction center protein, D1. Regulation of the gene family in response to changes in the light environment is complex, occurs at transcriptional and posttranscriptional levels, and results in an interchange of two different forms of D1 in the membrane. Expression of psbAI is downregulated under high-intensity light (high light) in contrast to induction of the other two family members. We show that, in addition to a known accelerated degradation of the psbAI message, promoter activity decreases upon exposure to high light. Unlike the other psbA genes, additional sequences upstream of the psbAI -35 element are required for expression. Mutagenizing the atypical psbAI -10 element from TCTCCT to TATAAT increased the magnitude of expression from both psbAI::lacZ and psbAI::luxAB fusions but did not affect downregulation under high light. Inactivation of group 2 sigma factor genes rpoD2 and sigC, in both wild-type and -10-element mutagenized backgrounds, resulted in elevated psbAI::luxAB expression but did not alter the response to high light. The results are consistent with redundancy of promoter recognition among cyanobacterial group 2 sigma factors. Electrophoretic mobility shift assays showed that the DNA sequence corresponding to the untranslated leader of the psbAI message binds one or more proteins from an S. elongatus extract. The corresponding region of psbAII efficiently competed for this binding activity, suggesting a shared regulatory factor among these disparately regulated genes.

Bacterial Proteins↗
PubMed1998

A screen for genes induced in the suprachiasmatic nucleus by light.

The mechanism by which mammalian circadian clocks are entrained to light-dark cycles is unknown. The clock that drives behavioral rhythms is located in the suprachiasmatic nucleus (SCN) of the brain, and entrainment is thought to require induction of genes in the SCN by light. A complementary DNA subtraction method based on genomic representational difference analysis was developed to identify such genes without making assumptions about their nature. Four clones corresponded to genes induced specifically in the SCN by light, all of which showed gating of induction by the circadian clock. Among these genes are c-fos and nur77, two of the five early-response genes known to be induced in the SCN by light, and egr-3, a zinc finger transcription factor not previously identified in the SCN. In contrast to known examples, egr-3 induction by light is restricted to the ventral SCN, a structure implicated in entrainment.

Animals↗
PubMed2006

Applying Pulse Amplitude Modulation (PAM) fluorometry to microalgae suspensions: stirring potentially impacts fluorescence.

The use of microalgae suspensions in PAM-fluorometers such as the Water-PAM (Walz GmbH, Germany) presents the problem of maintaining a homogeneous sample. The Water-PAM is marketed with an optional accessory for stirring the sample within the cuvette while in the emitter-detector (ED) unit. This stirring device can help to prevent cells from settling out of suspension over the time-course of chlorophyll-a fluorescence measurements. The ED unit was found to provide a vertically heterogeneous light environment and, therefore, cells within a single sample can exist in different quenched states. Enhancing cell movement by stirring was found to substantially influence measured fluorescence yield while performing induction curve and rapid light curve analyses. This is likely to result from relatively unquenched cells outside the main light-path moving into a higher light region and thus emitting disproportionately more fluorescence than quenched cells. Samples containing cells with high sinking rates or motile species may encounter similar (but reduced) problems. This effect can be mitigated by: (a) reducing analysis time to minimise the distance cells can sink/swim during the measurement procedure and avoiding the necessity of stirring; (b) limiting the proportion of sample outside the light path by minimising sample volume or; (c) by activating the stirrer only for short periods between saturation pulses and allowing enough time after stirring for quenching to stabilise before activation of the saturation pulse. Alternatively, modifications to the instrument providing a vertical dimension to the LED-array could resolve the issue by providing a more homogeneous light environment for the sample.

Chlorophyll↗
PubMed1985

Influence of skin illumination on serum acetylcholinesterase of the rabbit.

The effects of skin illumination (continuous or discontinuous colorless or yellow filtered white light) on acetylcholinesterase levels are tested on rabbit serum. Significant increases in acetylcholinesterase are observed with continuous and discontinuous colorless filtered white light as compared to controls.

Acetylcholinesterase↗
PubMed2001

Morphological changes in the rat kidney following long-term diabetes.

The morphological basis of diabetic nephropathy has been studied using light and electron microscopy. Kidneys of streptozotocin-induced diabetic rats were examined on the light microscope at 4 weeks and 8 months after induction of diabetes mellitus. In addition, the 8-month diabetic kidneys were examined with the electron microscope. Renal hypertrophy was evidenced by the increase in the weight of kidneys of diabetic rats. Whilst the diabetic kidneys were approximately twice as large after 4 weeks they were only 30% larger compared to age-matched controls after 8 months of induction of diabetes. After 4 weeks, light microscopy revealed dilated tubules within the cortex of the diabetic kidneys. Light microscopy showed a significant amount of destruction of the distal convoluted tubules while electron microscopy revealed a spectrum of damage that included basement membrane thickening, loss of podocytic foot processes, disruption of tubular basal infoldings and their related mitochondria and fibrosis of the tubules 8 months after induction of diabetes. It is concluded that renal hypertrophy persists after a prolonged occurrence of diabetes but the extensive damage and loss of renal tissue including the loss of the foot processes of podocytes might be partly responsible for the clinical presentation of diabetic nephropathy.

Animals↗
PubMed1995

Induction of heme oxygenase 1 in the retina by intense visible light: suppression by the antioxidant dimethylthiourea.

The effect of intense visible light (light damage) on the expression of heme oxygenase 1 (HO-1), a protein induced by oxidative stress, was investigated in the rat retina. A sensitive reverse transcription-PCR assay demonstrated the expression of mRNA for HO-1 as well as HO-2, the noninducible HO form, in the normal retina. As analyzed by Northern blotting, however, HO-1 mRNA was barely detectable under normal circumstances. After exposure to intense visible light, retinas had markedly higher HO-1 mRNA levels than unexposed controls, with increases up to 52- and 98-fold at 12 and 24 hr of exposure, respectively. Intense light exposure also resulted in an increase in HO-1 protein. In contrast, no appreciable change in HO-2 mRNA or protein was observed. The increase in HO-1 message was more pronounced in rats previously reared in the dark than in those reared in a weak cyclic-light environment. A marked decrease from the high level of HO-1 mRNA induced by light insult was observed when the animals were allowed to recover in the dark for 24 hr after light exposure. Most important, treatment of animals with 1,3-dimethylthiourea, a synthetic antioxidant, prior to light exposure effectively blocked the increase in HO-1 mRNA. Thus, HO-1 is a sensitive marker for assessing light-induced insult in the retina. Since increased expression of HO-1 is thought to be a cellular defense against oxidative damage, its expression may play an important role in protecting the retina against light damage.

Amino Acid Sequence↗
PubMed1980

Intermittent swimming in live sea urchin sperm.

Sperm of the sea urchin Tripneustes gratilla repeatedly start and stop swimming when suspended in seawater and observed by dark-field microscopy. While in the quiescent state, which usually lasts about a second, the sperm assume s shape resembling a cane, with a sharp bend of approximately 3.4 rad in the proximal region of the flagellum and very little curvature in the rest of the flagellum except for a slight curve near the tip. The occurrence of quiescence requires the presence of at least 2 mM Ca2+ in the seawater, and the percentage of sperm quiescent at any one time increases substantially when the sperm are illuminated with blue light. With intense illumination, close to 100% of the sperm become quiescent, and this percentage decreases gradually to approximately 0.3% over a 10(4)-fold decrease in light intensity. An increased concentration of K+ in the seawater also increases the percentage of quiescence, with a majority of the sperm being quiescent in seawater containing 80 mM KCl. The induction of quiescence by light or by increased KCl is completely inhibited by 10 micrometers chlorpromazine, and approximately 90% inhibited by 1 mM procaine or sodium barbital. Sperm treated with the divalent-cation ionophore A23187 swim quite normally, although for a relatively short period, in artificial seawater lacking divalent cations, but are abruptly arrested upon addition of 0.04--0.2 mM free Ca2%. The flagellar waveform of these arrested sperm is almost identical to that of light-induced quiescence in the live sperm. The results support the hypothesis that quiescence is induced by a rise in intracellular Ca2%, perhaps as a consequence of a membrane depolarization, and that it is similar to the arrest response in cilia.

Animals↗
PubMed2003

Light plays a key role in the modulation of heat shock response in the cyanobacterium Synechocystis sp PCC 6803.

The heat shock response is generally characterized by an immediate, intense, and transient activation of gene expression, resulting in the elevated synthesis of heat shock proteins. We found that light modulates these characteristics of the heat shock response in cyanobacteria. Light accelerated the heat induction of htpG, groESL1, groEL2, and hspA, in Synechocystis sp. PCC 6803. In the dark, heat shock response of all the heat shock genes except hspA was not as intense as in the light and no transient peak was detected within 3h after heat shock over the time course of the hspA and groESL1 mRNA accumulation. There was an apparent relationship between the enhancement of the heat shock gene transcription in the light and the level of reduced plastoquinone in the photosynthetic electron transport system. Light affected the transcription, but not the stability of the mRNA of heat shock genes, although the stability was quite different, depending on the heat shock gene. Light also enhanced both the accumulation of GroEL under heat stress and the acquired thermo-tolerance.

Bacterial Proteins↗
PubMed1995

Distribution of Fos-positive neurons in cortical and subcortical structures after picrotoxin-induced convulsions varies with seizure type.

The distribution of Fos protein was mapped in rat brain following a single non-focal convulsive seizure. Single seizures were induced with intravenous picrotoxin in unhandled animals housed in isolation. Different convulsive behaviours occurred unpredictably. The least severe seizures were predominantly localised to the face, head and forelimbs, without loss of posture control (restricted seizures). The most extensive seizures affected all limbs and trunk, sometimes with falling (generalised seizures). There was a correlation between seizure behaviour and distribution of Fos induction. After restricted seizures, Fos was induced at highest levels in neocortex and piriform cortex and was prominent in entorhinal cortex, caudal-ventral caudate-putamen and amygdala. Regions of thalamus were consistently and lightly labelled, but Fos induction did not occur in hippocampus. After generalised seizures, there was Fos induction in cortex but less than after restricted seizures and, in three of four animals, also in dentate gyrus, hippocampus and subiculum. There was occasional or variable labelling of thalamus, basolateral amygdala and caudate-putamen. One animal with generalised seizures showed no hippocampal Fos induction. The findings indicate that picrotoxin induces seizures with at least two different patterns of neuronal involvement. The cortex, part of the caudate-putamen, amygdala and thalamus are involved in restricted seizures while the hippocampus, cortex and thalamus are involved in generalised seizures. The results do not support the view that generalised seizures are a progression from restricted forms. Cortical Fos involvement is entirely consistent with the participation of cortex in non-focal epilepsy. In these non-focal seizures, the dentate-hippocampus may be a source of excitation to cortex in the generalised group while the cortex appears to be the predominant site of excitation in the restricted group.

Animals↗