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PubMed1979

[Streptococcus group A resistance to tetracycline: its spread and transduction].

The study on antibiotics resistance of group A streptococci isolated in 1977 showed that the number of the antibiotic resistant strains had significantly increased as compared to the data of 1960. High percentage (53%) of the cultures with multiple resistance was noted. It was observed that the number of the streptococcal cultures resistant to erythromycin and chloramphenicol decreased while the number of the strains resistant to tetracyclines increased. The level of resistance to tetracycline increased more than 2 times from 1960 and in some cases reached 125 and 250 gamma/ml. The wide spread of tetracycline resistance was evident of the presence of the mechanism of the marker transduction. Possible transduction of this feature was studied. Microbe-free phagolysates obtained by induction with UV-light from the strains with multiple antibiotic resistance were used as the donor material in the experiment on transduction. Principal possibility of transducing resistance to tetracycline from 2 donors to 4 recipients at a frequency of 10(-6) was shown.

Bacteriophages↗
PubMed1984

[Nerve regeneration through a venous graft in the rat. Preliminary results].

An experimental study of nerve regeneration in rats was realized after sectioning 8 mm of the sciatic nerve and interpositioning a vein-graft to replace the portion of nerve which has been removed. The vein-graft was taken at the neck level, far away from the point of suture between vein and nerve, a procedure which seems to prevent the problems of scabbing. A histological and electrophysiological analysis was carried out on 16 grafts, over periods ranging from 4 weeks to 4 months. The nerve and venous dissections were realized under a stereoscopic microscope. A certain degree of amyotrophy appeared in the external-posterior region of the thigh, directly related to the muscular dissection and the partial paralysis caused by the section of the common peroneal nerve. The electrophysiological recordings in vivo provide proof of nerve regeneration but reveal the absence of any correlation between the time of recovery and the time of induction. Examination under the light microscope confirms the regeneration of the nerve inside of the vein-graft, with an augmentation of myelin sheaths, which increase with time both in number and in thickness. The vein-wall acts as a guide but the passage of a few nervous filaments outside of the graft itself is observed. Examination under the electron microscope furnishes important information on myelin sheaths. The results are of excellent quality, but to better appreciate and evaluate them, we envisage a further study, this time to be carried out on another animal species.

Animals↗
PubMed1996

Differential distribution of CaM kinases and induction of c-fos expression by flashing and sustained light in rat retinal cells.

PURPOSE: To examine the expression of c-fos proto-oncogene and phosphorylation of cAMP responsive element binding (CREB) protein in the rat retina after changes in the light-dark condition. METHODS: Rats were exposed to both steady light and flashing light and were killed at the end of light exposure. The retinas were analyzed by in situ hybridization using single-stranded RNA probes for c-fos transcripts and by immunocytochemistry using phosphoSer-133 specific CREB antiserum, anti-calcium calmodulin dependent protein (CaM) kinase II, and anti-CaM kinase IV. RESULTS: c-fos mRNA was expressed in the outer half of the inner nuclear layer (INL) and in the ganglion cell layer (GCL) after 30 minutes of sustained light. After 30 minutes of flashing light, c-fos expression also was detected in the inner border of the INL. Phosphorylated CREB immunoreactive nuclei had similar distribution after steady and flashing light. Both CaM kinase II and CaM kinase IV, which phosphorylate CREB at Ser 133 in vitro, were expressed in the GCL and in the INL. CaM kinase II, however, was localized in the inner border of the INL, whereas CaM kinase IV was distributed in the outer half of the INL. CONCLUSIONS: These results suggest that the differential expression of c-fos mRNA induced by flashing and sustained light may reflect the CREB phosphorylation by CaM kinases in a different subpopulation of retinal cells.

Animals↗
PubMed1993

Phase-shifting mechanisms in the mammalian circadian system: new light on the carbachol paradox.

A variety of evidence now suggests that excitatory amino acid receptors mediate the effects of light on the circadian system of mammals. However, the ACh agonist carbachol is the only agent that has been reported to "mimic" the phase-shifting effects of light in vivo. Because the other published evidence for the involvement of ACh in light-mediated phase shifts is weak, we have referred to this situation as "the carbachol paradox." In the present study, we found that the administration of NMDA receptor antagonists could prevent carbachol-induced phase shifts of the circadian rhythm of wheel-running activity recorded from the hamster. In addition, we found that carbachol-induced phase shifts, unlike those produced by light, are not accompanied by induction of Fos-like immunoreactivity in the suprachiasmatic nucleus (SCN). Our data are simply explained by the assumption that the intraventricular administration of carbachol causes phase shifts through a pathway distinct from that of light. Alternatively, if carbachol is acting via the light input pathway, then it must do so by a mechanism independent of Fos induction in the SCN. In either case, elucidating the mechanisms by which carbachol acts in the circadian system may provide novel insights into the cellular events by which phase shifts are generated.

Animals↗
PubMed2005

A dip in the chlorophyll fluorescence induction at 0.2-2 s in Trebouxia-possessing lichens reflects a fast reoxidation of photosystem I. A comparison with higher plants.

An unusual dip (compared to higher plant behaviour under comparable light conditions) in chlorophyll fluorescence induction (FI) at about 0.2-2 s was observed for thalli of several lichen species having Trebouxia species (the most common symbiotic green algae) as their native photobionts and for Trebouxia species cultured separately in nutrient solution. This dip appears after the usual O(J)IP transient at a wide range of excitation light intensities (100-1800 micromol photons m(-2) s(-1)). Simultaneous measurements of FI and 820-nm transmission kinetics (I(820)) with lichen thalli showed that the decreasing part of the fluorescence dip (0.2-0.4 s) is accompanied by a decrease of I(820), i.e., by a reoxidation of electron carriers at photosystem I (PSI), while the subsequent increasing part (0.4-2 s) of the dip is not paralleled by the change in I(820). These results were compared with that measured with pea leaves-representatives of higher plants. In pea, PSI started to reoxidize after 2-s excitation. The simultaneous measurements performed with thalli treated with methylviologen (MV), an efficient electron acceptor from PSI, revealed that the narrow P peak in FI of Trebouxia-possessing lichens (i.e., the I-P-dip phase) gradually disappeared with prolonged MV treatment. Thus, the P peak behaves in a similar way as in higher plants where it reflects a traffic jam of electrons induced by a transient block at the acceptor side of PSI. The increasing part of the dip in FI remained unaffected by the addition of MV. We have found that the fluorescence dip is insensitive to antimycin A, rotenone (inhibitors of cyclic electron flow around PSI), and propyl gallate (an inhibitor of plastid terminal oxidase). The 2-h treatment with 5 microM nigericin, an ionophore effectively dissipating the pH-gradient across the thylakoid membrane, did not lead to significant changes either in FI nor I(820) kinetics. On the basis of the presented results, we suggest that the decreasing part of the fluorescence dip in FI of Trebouxia-lichens reflects the activation of ferredoxin-NADP(+)-oxidoreductase or Mehler-peroxidase reaction leading to the fast reoxidation of electron carriers in thylakoid membranes. The increasing part of the dip probably reflects a transient reduction of plastoquinone (PQ) pool that is not associated with cyclic electron flow around PSI. Possible causes of this MV-insensitive PQ reduction are discussed.

Antimycin A↗
PubMed1988

[Control of chlorophyll a synthesis by phytochrome and cryptochrome in the red alga Corallina elongata Ellis et Soland].

Chlorophyll a synthesis in the red alga Corallina elongata is controlled by phytochrome and by a specific blue light photoreceptor. Although the estimated photoequilibrium of phytochrome is similar in blue and red light, the amount of chlorophyll accumulated is greater in blue light, which implies the action of cryptochrome, according to the criteria for the specific blue light photoreceptor involvement. The amount of chlorophyll synthesized is greater when the level of photoequilibrium approaches 65% (in blue and red light) than with higher levels (72.7% in white light and 70.8% in green light). The action of phytochrome is demonstrated by the induction of chlorophyll synthesis after red pulses and the reversion after far red pulses. The reversion is not complete but the percentage of reversibility is high (85-90%). The amount of chlorophyll accumulated is greater in darkness after the application of red light pulses than in white light after the same light pulses. The induction of chlorophyll synthesis is greater after red pulses than after continuous red light. The existence of a fast destruction of chlorophyll in continuous light is observed. This destruction is greater in the high photoequilibrium of phytochrome (70-72%). The turnover times and the induction mechanism of chlorophyll synthesis must be very fast. This indicates the existence of a possible rapid adaptation to the change in light quality and intensity in the marine system.

Chlorophyll↗
PubMed2003

Living by the calendar: how plants know when to flower.

Reproductive processes in plants and animals are usually synchronized with favourable seasons of the year. It has been known for 80 years that organisms anticipate seasonal changes by adjusting developmental programmes in response to daylength. Recent studies indicate that plants perceive daylength through the degree of coincidence of light with the expression of CONSTANS, which encodes a clock-regulated transcription factor that controls the expression of floral-inductive genes in a light-dependent manner.

Circadian Rhythm↗
PubMed1999

The relationship between the effects of UV light and thermal shock on gametes and the viability of early developmental stages in a marine teleost fish, the sea bass (Dicentrarchus labrax L.).

To improve the efficiency of gynogenetic induction, the effects of UV light and thermal shock on gametes were investigated in the sea bass. Exposure of sperm to UV light (>/=15 000 erg mm-2) reduced the amount of motile spermatozoa, without affecting the duration of motility in the spermatozoa that remained motile. The Hertwig effect was elicited in eggs fertilized with sperm exposed to >/=35 000 erg mm-2 of UV light, indicating the inactivation of the DNA of the spermatozoa while retaining their ability to trigger development. Resulting embryos (24 chromosomes; one NOR) exhibited the haploid syndrome and died at hatch. Diploidy was restored in eggs fertilized with irradiated sperm by blocking meiosis II with a thermal shock (0 +/- 0.5 degrees C for 10 min, starting 5 min after fertilization). Resulting larvae ( approximately 35% survival at hatching) had 48 chromosomes, one or two NOR and no paternal chromosome fragments (gynogenetic diploids). In eggs fertilized with sperm not exposed to UV light, the same thermal shock induced 100% triploidy (72 chromosomes; one, two or three NOR), with 70% survival at hatching. Multifactorial ANOVA showed that, compared to external factors (sperm diluent, UV light and thermal shock), the contribution of broodstock to the viability of the early developmental stages was not significant (P > 0.05). Effects of the thermal shock were most evident after fertilization (30.7%) but disappeared (0%) at hatching, suggesting that the lower survival of triploids is a consequence of handling, not of the triploid condition per se. However, effects of UV light increased through development (42.5-69.7%), probably reflecting cumulative deficits in protein synthesis.

Animals↗
PubMed1995

Signal-transduction pathways controlling light-regulated development in Arabidopsis.

All metazoan cells are able to make decisions about cell division or cellular differentiation based, in part, on environmental cues. Accordingly, cells express receptor systems that allow them to detect the presence of hormones, growth factors and other signals that manipulate the regulatory processes of the cell. In plants, an unusual signal-light-is required for the induction and regulation of many developmental processes. Past physiological and molecular studies have revealed the variety and complexity of plant responses to light but until recently very little was known about the mechanisms of those responses. Two major breakthroughs have allowed the identification of some photoreceptor signalling intermediates: the identification of photoreceptor and signal transduction mutants in Arabidopsis, and the development of single-cell microinjection assays in which outcomes of photoreceptor signalling can be visualized. Here, we review recent genetic advances which support the notion that light responses are not simply endpoints of linear signal transduction pathways, but are the result of the integration of a variety of input signals through a complex network of interacting signalling components.

Arabidopsis↗
PubMed1995

Regulation of Early Light-Inducible Protein Gene Expression by Blue and Red Light in Etiolated Seedlings Involves Nuclear and Plastid Factors.

Early light-inducible proteins (ELIPs) are nuclear-encoded chloroplast proteins whose genes are transiently transcribed during the greening process of etiolated plants. In the present work the regulation of ELIP gene expression by blue and red light has been investigated in plumulas of etiolated pea plants (Pisum sativum). The results show that the steady-state level of ELIP transcripts is controlled by a combined action of phytochrome and blue light receptor systems and, in addition, depends on the age of the seedlings. Both a low-light fluence system of blue and a very-low-fluence system of red light are involved in ELIP induction. The threshold for accumulation of ELIP transcripts was as low as 10-5 [mu]E m-2 s-1 for both light qualities but a different pattern of accumulation was obtained in blue and in red light. Blue light not only acts at the level of transcription but also regulates the stability of the ELIP transcripts in a light intensity-dependent manner. Moreover, it is shown that product(s) of nuclear gene(s) negatively regulate the steady-state level of ELIP transcripts during the 1st h of illumination with red light. Preillumination of seedlings with white light abolishes this repression. Accumulation of ELIP transcripts requires "plastid factors" in both blue and red light qualities.

Journal Article↗
PubMed1994

A comparison of the DNA-damaging, the cytotoxic and genotoxic properties of tetracycline in human fibroblasts in the presence and absence of light.

The reduction of the colony-forming ability, the induction of DNA strand breaks and DNA repair were determined in human fibroblasts after treatment with tetracycline (TC) in the presence and absence of light. In all experiments human fibroblasts were more sensitive to incubations of TC in the light than in the dark. Induction of DNA single-strand breaks and DNA repair were detected in the cells after a 1-h incubation with TC under light but not in the dark. In contrast to these results, TC induced single-strand breaks in isolated PM2 DNA in the dark, however, to a lower extent than in the presence of light. In both cases strand break formation was totally suppressed by adding catalase. The formation of a TC-derived radical by ESR and a decomposition product by UV-vis spectroscopy was observed in the presence and absence of light; their rate of formation in the dark was much smaller than in the light.

Cell Line↗
PubMed1998

Ultraviolet light induces apoptosis via direct activation of CD95 (Fas/APO-1) independently of its ligand CD95L.

Induction of apoptosis in keratinocytes by UV light is a critical event in photocarcinogenesis. Although p53 is of importance in this process, evidence exists that other pathways play a role as well. Therefore, we studied whether the apoptosis-related surface molecule CD95 (Fas/APO-1) is involved. The human keratinocyte cell line HaCaT expresses CD95 and undergoes apoptosis after treatment with UV light or with the ligand of CD95 (CD95L). Incubation with a neutralizing CD95 antibody completely prevented CD95L-induced apoptosis but not UV-induced apoptosis, initially suggesting that the CD95 pathway may not be involved. However, the protease CPP32, a downstream molecule of the CD95 pathway, was activated in UV-exposed HaCaT cells, and UV-induced apoptosis was blocked by the ICE protease inhibitor zVAD, implying that at least similar downstream events are involved in CD95- and UV-induced apoptosis. Activation of CD95 results in recruitment of the Fas-associated protein with death domain (FADD) that activates ICE proteases. Immunoprecipitation of UV-exposed HaCaT cells revealed that UV light also induces recruitment of FADD to CD95. Since neutralizing anti-CD95 antibodies failed to prevent UV-induced apoptosis, this suggested that UV light directly activates CD95 independently of the ligand CD95L. Confocal laser scanning microscopy showed that UV light induced clustering of CD95 in the same fashion as CD95L. Prevention of UV-induced CD95 clustering by irradiating cells at 10 degrees C was associated with a significantly reduced death rate. Together, these data indicate that UV light directly stimulates CD95 and thereby activates the CD95 pathway to induce apoptosis independently of the natural ligand CD95L. These findings further support the concept that UV light can affect targets at the plasma membrane, thereby even inducing apoptosis.

Antibodies↗
PubMed2007

Interactive effects of leaf damage, light intensity and support availability on chemical defenses and morphology of a twining vine.

In a greenhouse study, we evaluated the effect of the light environment and support availability on the induction of tropane alkaloids (TAs) after leaf damage in the twining vine Convolvulus arvensis. We also tested whether leaf damage modifies the phenotypic responses of the plant to shade and physical support. We found a consistent pattern of induction of TAs after leaf damage in each environmental condition. The induction of TAs was differentially affected by combinations of support and light treatments. In the sun, prostrate and climbing vines exhibited similar induced responses. In the shade, prostrate vines showed greater induced responses. Thus, vines showed the greatest chemical induction when damage occurred in a resource-poor environment (shade), and there was no cue (support) of future increase in resource uptake. Damaged plants showed reduced plasticity to shading in leaf shape and internodes and petiole length in comparison with control, undamaged plants. Herbivory and/or induced responses to herbivory may limit adaptive plant responses to the environment. Therefore, the negative consequences of herbivory on plant fitness might be magnified in a context of changing environments.

Convolvulus↗
PubMed1984

DNA repair and induction of plasminogen activator in human fetal cells treated with ultraviolet light.

We have tested human fetal fibroblasts for development associated changes in DNA repair by utilizing nucleoid sedimentation as an assay for excision repair. Among skin fibroblasts the rate of excision repair was significantly higher in non-fetal cells than in fibroblasts derived from an 8 week fetus; this was evident by a delay in both the relaxation and the restoration of DNA supercoiling in nucleoids after irradiation. Skin fibroblasts derived at 12 week gestation were more repair proficient than those derived at 8 week gestation. However, they exhibited a somewhat lower rate of repair than non-fetal cells. The same fetal and non-fetal cells were also tested for induction of the protease plasminogen activator (PA) after u.v. irradiation. Enhancement of PA was higher in skin fibroblasts derived at 8 week than in those derived at 12 week gestation and was absent in non-fetal skin fibroblasts. These results are consistent with our previous findings that in human cells u.v. light-induced PA synthesis is correlated with reduced DNA repair capacity. Excision repair and PA inducibility were found to depend on tissue of origin in addition to gestational stage, as shown for skin and lung fibroblasts from the same 12 week fetus. Lung compared to skin fibroblasts exhibited lower repair rates and produced higher levels of PA after irradiation. The sedimentation velocity of nucleoids, prepared from unirradiated fibroblasts, in neutral sucrose gradients with or without ethidium bromide, indicated the presence of DNA strand breaks in fetal cells. It is proposed that reduced DNA repair in fetal cells may result from alterations in DNA supercoiling, and that persistent DNA strand breaks enhance transcription of PA gene(s).

Cell Line↗