PubMed Health⌕ Search

Biomedical subjects

A Fehér

Publications and source records attributed to A Fehér.

At least 19 recordsLinked to original sources
PubMed2006

Identification and characterization of genes associated with the induction of embryogenic competence in leaf-protoplast-derived alfalfa cells.

Alfalfa leaf protoplast-derived cells can develop into somatic embryos depending on the concentration of 2,4-dichlorophenoxyacetic acid (2,4-D) in the initial culture medium. In order to reveal gene expression changes during the establishment of embryogenic competence, we compared the cell types developed in the presence of 1 and 10 microM 2,4-D, respectively, at the time of their first cell divisions (fourth day of culture) using a PCR-based cDNA subtraction approach. Although the subtraction efficiency was relatively low, applying an additional differential screening step allowed the identification of 38 10 microM 2,4-D up-regulated transcripts. The corresponding genes/proteins were annotated and representatives of various functional groups were selected for more detailed gene expression analysis. Real-time quantitative PCR (RT-QPCR) analysis was used to determine relative expression of the selected genes in 2,4-D-treated leaves as well as during the whole process of somatic embryogenesis. Gene expression patterns confirmed 2,4-D inducibility for all but one of the 11 investigated genes as well as for the positive control leafy cotyledon1 (MsLEC1) gene. The characterized genes exhibited differential expression patterns during the early induction phase and the late embryo differentiation phase of somatic embryogenesis. Genes coding for a GST-transferase, a PR10 pathogenesis-related protein, a cell division-related ribosomal (S3a) protein, an ARF-type small GTPase and the nucleosome assembly factor family SET protein exhibited higher relative expression not only during the induction of somatic embryogenesis but at the time of somatic embryo differentiation as well. This may indicate that the expression of these genes is associated with developmental transitions (differentiation as well as de-differentiation) during the process of somatic embryogenesis.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2000

Multiple cyclin-dependent kinase complexes and phosphatases control G2/M progression in alfalfa cells.

Reversible phosphorylation of proteins by kinases and phosphatases plays a key regulatory role in several eukaryotic cellular functions including the control of the division cycle. Increasing numbers of sequence and biochemical data show the involvement of cyclin-dependent kinases (CDKs) and cyclins in regulation of the cell cycle progression in higher plants. The complexity represented by different types of CDKs and cyclins in a single species such as alfalfa, indicates that multicomponent regulatory pathways control G2/M transition. A set of cdc2-related genes (cdc2Ms A, B, D and F) was expressed in G2 and M cells. Phosphorylation assays also revealed that at least three kinase complexes (Cdc2Ms A/B, D and F) were successively active in G2/M cells after synchronization. Interaction between alfalfa mitotic cyclin (Medsa;CycB2;1) and a kinase partner has been reported previously. The present yeast two-hybrid analyses showed differential interaction between defined D-type cyclins and Cdc2Ms kinases functioning in G2/M phases. Localization of Cdc2Ms F kinase to the preprophase band (PPB), the perinuclear ring in early prophase, the mitotic spindle and the phragmoplast indicated a pivotal role for this kinase in mitotic plant cells. So far limited research efforts have been devoted to the functions of phosphatases in the control of plant cell division. A homologue of dual phosphatase, cdc25, has not been cloned yet from alfalfa; however tyrosine phosphorylation was indicated in the case of Cdc2Ms A kinase and the p(13suc1)-bound kinase activity was increased by treatment of this complex with recombinant Drosophila Cdc25. The potential role of serine/threonine phosphatases can be concluded from inhibitor studies based on okadaic acid or endothall. Endothall elevated the kinase activity of p(13suc1)-bound fractions in G2-phase alfalfa cells. These biochemical data are in accordance with observed cytological abnormalities. The present overview with selected original data outlines a conclusion that emphasizes the complexity of G2/M regulatory events in flowering plants.

CDC2 Protein Kinase↗
PubMed2000

Inhibition of serine/threonine-specific protein phosphatases causes premature activation of cdc2MsF kinase at G2/M transition and early mitotic microtubule organisation in alfalfa.

Reversible phosphorylation of serine/threonine residues of cell cycle-regulatory proteins is one of the key molecular mechanisms controlling eukaryotic cell division. In plants, the protein kinase partners (i.e. p34cdc2/CDC28-related kinases) have been extensively studied, while the role of counter-acting protein phosphatases is less well understood. We used endothall (ET) as a cell-permeable inhibitor of serine/threonine-specific protein phosphatases to alter cytological and biochemical characteristics of cell division in cultured alfalfa cells. A high concentration of ET (10 and 50 microM) inhibited both protein phosphatases 1 and 2 (PP1 and PP2A), while a low concentration (1 microM) of ET-treatment primarily reduced the PP2A activity. High concentrations of the inhibitor increased the frequency of hypercondensed early and late prophase chromosomes that could not enter metaphase. In contrast, a low concentration of ET did not interfere with chromosomal events but caused significant alterations in the organisation of microtubules. Exposure of cells to 1 microM ET resulted in disturbance of preprophase band formation, increase in the number of nuclei with prophase microtubule assembly, premature polarisation of the spindle, and abnormal phragmoplast maturation. Under the same conditions, the ET-treated cells exhibited an early increase in cdc2MsF kinase activity. These results suggest that PP2A contributes to the control of mitotic kinase activities and microtubule organisation. Normal chromosome condensation and mitotic progression are dependent on both PP1 and PP2A activities. The presented data support the functional role of protein phosphatases in the co-ordination of chromosomal and microtubule events in dividing plant cells.

Chromosomes↗
PubMed2000

A novel aldose/aldehyde reductase protects transgenic plants against lipid peroxidation under chemical and drought stresses.

Rapid accumulation of toxic products from reactions of reactive oxygen species (ROS) with lipids and proteins significantly contributes to the damage of crop plants under biotic and abiotic stresses. Here we have identified a stress-activated alfalfa gene encoding a novel plant NADPH-dependent aldose/aldehyde reductase that also exhibited characteristics of the homologous human enzyme. The recombinant alfalfa enzyme is active on 4-hydroxynon-2-enal, a known cytotoxic lipid peroxide degradation product. Ectopic synthesis of this enzyme in transgenic tobacco plants provided considerable tolerance against oxidative damage caused by paraquat and heavy metal treatment. These transformants could also resist a long period of water deficiency and exhibited improved recovery after rehydration. We found a reduced production of lipid peroxidation-derived reactive aldehydes in these transformed plants under different stresses. These studies reveal a new and efficient detoxification pathway in plants.

Adaptation, Physiological↗
PubMed2000

[Clinical study of zirconium oxide bridges in the posterior segments fabricated with the DCM system].

Today's dental reconstructive therapeutic concepts require restoration of high esthetic quality and excellent biocompatibility. Full ceramic reconstructions accomplish these requirements but only for anterior teeth and premolars. For all-ceramic bridges the mechanical strength was insufficient to withstand the posterior chewing forces. Frequently the interdental connectors cracked, and the only way to prevent these fractures was to overconture the connectors to a size of approx. 16 mm2. The high-tech ceramic zirconia is a potential alternative for three-to five-unit full ceramic bridges in the functionally loaded posterior segments. Experimental zirconia bridges which were fabricated using the DCM system (Direct Ceramic Machining System at the ETH Zurich, were tested in vitro. The frameworks were digitally enlarged by 20% and were easily milled from a presintered yet porous zirconia blank. After the milling process, the framework was densely sintered and shrank to its original size. Due to these positive in-vitro results a clinical investigation was started. 22 veneered zirconia bridges were luted; 19 molars and 25 premolars were prepared. The connectors, max. 7 mm2, of all these bridges, have been functionally loaded by antagonists. After a mean observation time of 385 days (307 days to 488 days), all 22 bridges did not show any cracks in the framework or in the veneering porcelain. The patients commented particularly on the low heat conduction rate of zirconia. The only endodontic problem which occurred could not be directly connected to the type of bridge framework. The reliability of zirconia bridges in this investigation was connected to the DCM-Process. No statement about other zirconia-systems can be made on the results of this study.

Dental Alloys↗
PubMed1999

Late maturation of visual spatial integration in humans.

Visual development is thought to be completed at an early age. We suggest that the maturation of the visual brain is not homogeneous: functions with greater need for early availability, such as visuomotor control, mature earlier, and the development of other visual functions may extend well into childhood. We found significant improvement in children between 5 and 14 years in visual spatial integration by using a contour-detection task. The data show that long-range spatial interactions-subserving the integration of orientational information across the visual field-span a shorter spatial range in children than in adults. Performance in the task improves in a cue-specific manner with practice, which indicates the participation of fairly low-level perceptual mechanisms. We interpret our findings in terms of a protracted development of ventral visual-stream function in humans.

Adolescent↗
PubMed1999

[Effectiveness of pinaverium bromide therapy on colonic motility disorders in irritable bowel syndrome].

The special patterns of the slow wave activity in irrittable bowel syndrome by means of surface electromyography were examined and the effect of pinaverium bromide on the symptoms and on the colonic motility in this disease was estimated. Twenty two patients with irritable bowel syndrome and 7 healthy controls were selected to the study. The clinical symptoms were abdominal pain and bloating in all patients, constipation in 9, and diarrhoea in 6 cases. Surface electromyography was carried out before and on the 14th day of the treatment with pinaverium bromide (50 mg t. i. d). The colonic motility was analysed in a 2 hour fasting and a 2 hour postprandial period following a standard (800 kCal) meal. The slow wave frequency of 0.01-0.04 Hz were selected and analysed. The mean frequency of activity peaks (n/10 min) and power-index (area under curve, microV 10 min) were measured. For statistical analysis Student's t-test was applied. Electromyogram of patients with irritable bowel syndrome showed a significant increase of the measured colonic motility parameters both in fasting and postprandial states. Fourteen days of pinaverium bromide treatment was able to significantly reduce the intensity of the colonic motor activity. Administration of pinaverium bromide completely released in 6 and significantly improved the abdominal pain in other 12 patients, while the bloating disappeared in 12 and was significantly improved in 5 from 22 patients. Pinaverium bromide was able to normalise the stool frequency: the weekly number of stools was decreased from 16 to 7 in the patients complaining diarrhoea ant it was increased from 2 to 6 in the patients with constipation.

Calcium Channel Blockers↗
PubMed1999

Chemical models of cytochrome P450 catalyzed insecticide metabolism. Application to the oxidative metabolism of carbamate insecticides.

Cytochrome P450 (CP450) catalyzed oxidative metabolism of carbofuran (1), carbaryl (2), and pirimicarb (3) has been modeled using biomimetic oxidations catalyzed by iron(III) tetraarylporphyrins. Oxidation products of 1 were identified by comparison of HPLC retention times measured under standardized conditions for metabolites synthesized and characterized by (1)H and (13)C NMR spectroscopy. Comparison of product distributions to in vivo metabolic profiles revealed that the H(2)O(2)/meso-tetrakis(pentafluorophenyl)porphyrin iron(III) chloride [Fe(TF(20)PP)] system mimics the action of insect CP450s against carbofuran. The effectiveness of this system was further demonstrated by the biomimetic oxidation of other carbamate insecticides (2 and 3) monitored by HPLC/electrospray MS. The predictive power of this biomimetic model was compared to that of knowledge-based expert systems. Although similar models were recently applied in pharmaceutical research, the usefulness of this approach has first been demonstrated for the prediction of metabolic profiles of agrochemicals.

Animals↗
PubMed1998

[Drug therapy of gastroesophageal reflux (a prospective controlled clinical trial)].

One year follow up(1.5, 3, 6, 12 months) study was established to examine the role of several classes of drugs in the treatment of reflux disease in 40 patients on the basis of objective control parameters (pH-metry, endoscopy, histology). The therapy was initiated, respectively, the different stage of severity (Savary-Miller): in stage 0 sucralfate + domperidone, in stage I and II: ranitidine + domperidone and in stage III-IV omeprazole was introduced. Our results proved that sucralfate + domperidone is curative on reflux oesophagitis in stage 0 cases. In stage I sucralfate and domperidone were effective in 3 of 9 cases, ranitidine + domperidone was optimal in 5 of 9, and omeprazole was required in 1 of 9 patients. In stage II, ranitidine + domperidone was effective only in 4 of 11 patients, and the initial therapy was modified to omeprazole in 7 of 11 patients to find the optimal drug in this stage. In stage III and IV only omeprazole showed curative effect and the doses required were 20 mg in 8 of 13 and 40 mg in 5 of 13 patients. The complaints improved in 34 of 40 patients after 6 weeks treatment, while histological healing of reflux oesophagitis was observed in 12 of 40 cases. After 3 months the endoscopic healing rate was 28/40, but histological healing could be reached after 6 months of optimal treatment in 30 of 40 cases. We can conclude, that the optimal drug selection may result a rapid improvement of complaints, but endoscopic and histological regeneration of the oesophageal mucosa is more graduated with time. The healing process of the reflux oesophagitis requires 3 months. Proton pump inhibitor drugs have an enhanced role in the treatment of gastrooesophageal reflux disease, and our results proved that the efficient and safety treatment of mild form (stage II) of disease requires the administration of proton pump inhibitors.

Adult↗
PubMed1998

Capillary chromatography/microelectrospray mass spectrometry used for the identification of putative cyclin-dependent kinase inhibitory protein in Medicago.

A home-built capillary chromatography/microelectrospray system was used for peptide mass mapping of a putative cyclin-dependent kinase inhibitor protein with molecular mass of 8.5 kDa. The masses of identified tryptic fragments were then input to a protein database search routine. Daughter ion scans were done only on the most abundant tryptic fragments. On the basis of protein database search results and tandem mass spectrometric measurements the bioactive protein was identified as ubiquitin.

Amino Acid Sequence↗
PubMed1998

Medial-point description of shape: a representation for action coding and its psychophysical correlates.

We describe a region-based shape representation that might be particularly useful from a biological perspective because it promotes the localization of objects, and object parts relative to each other. The proposed medial-point representation is similar to medial-axis type representations, but it is more compact. The medial points are those points along the medial axis that are equidistant from the longest segments of the boundary, therefore they represent the largest amount of edge information. The main advantage is that the original image can be reduced to a small number of points. We also provide psychophysical correlates of the representation for shapes with increasing complexity. Using a reverse mapping technique, we find that variations of contrast sensitivity within figures are defined by the shape of the bounding contour, and the peaks in the sensitivity maps correspond to the medial points of the proposed representation.

Computer Simulation↗
PubMed1997

[Treatment of achalasia of the cardia using thoracoscopic esophago-myotomy].

We performed left thoracoscopic esophagomyotomy in four patients suffering from achalasia cardiac. In one patients the esophageal mucosa was opened during the myotomy. This was sutured through thoracoscopy and the per os feeding of the patient started on the 8th postoperative day, while in the other three patients this was done on the 2nd postoperative day. The mean emission of the patients was on the 6th postoperative day. Comparison of the status before and 6 weeks following the operation was done on the basis of results of different examinations i. e. x-ray, esophago-gastroscopy, manometry, pH-metry, isotope test. The favourable results of the operations were declared as all examinations revealed marked improvement and all patients have better swallow function and 6-9 kg increase in body weight.

Adult↗
PubMed1997

Non-Fourier information in bandpass noise patterns.

Random dot patterns and white-noise luminance textures are widely used in psychophysical experiments to study low-level visual processes. Because these noise patterns are broadband, bandpass filtered versions are employed to limit their frequency content. It is not recognized, however, that bandpass noise patterns have amplitude-modulation (AM) components. The AM signal is not present in the Fourier spectrum, nonetheless, it is a valid signal for second-order mechanisms. We characterize the properties of the AM signal in bandpass noise textures: the relevant periodicities of the AM signal are always much lower than the actual passband; the upper frequency limit of the AM signal increases with the linear bandwidth. We present psychophysical data to demonstrate the perceptual significance of the AM signal in bandpass noise. We provide a method for obtaining AM-free bandpass patterns, and compare psychophysical performance in experiments employing AM-present and AM-free bandpass noise patterns as stereoscopic stimuli. The results show that the AM component contributes to stereoscopic discrimination performance at large disparities. We suggest that the low-frequency AM signal is a possible confounding factor in experiments employing bandpass noise textures, and that linear filtering can isolate spatial scales effectively only for linear systems.

Depth Perception↗
PubMed1997

Cell cycle phase specificity of putative cyclin-dependent kinase variants in synchronized alfalfa cells.

The eukaryotic cell division cycle is coordinated by cyclin-dependent kinases (CDKs), represented by a single major serine/threonine kinase in yeasts (Cdc2/CDC28) and a family of kinases (CDK1 to CDK8) in human cells. Previously, two cdc2 homologs, cdc2MsA and cdc2MsB, have been identified in alfalfa (Medicago sativa). By isolating cDNAs using a cdc2MsA probe, we demonstrate here that at least four additional cdc2 homologous genes are expressed in the tetraploid alfalfa. Proteins encoded by the new cdc2MsC to cdc2MsF cDNAs share the characteristic functional domains of CDKs with the conserved and plant-specific sequence elements. Transcripts from cdc2MsA, cdc2MsB, cdc2MsC, and cdc2MsE genes are synthesized throughout the cell cycle, whereas the amounts of cdc2MsD and cdc2MsF mRNAs peak during G2-to-M phases. The translation of Cdc2MsA/B, Cdc2MsD, and Cdc2MsF proteins follows the pattern of transcript accumulation. The multiplicity of kinase complexes with cell cycle phase-dependent activities was revealed by in vitro phosphorylation experiments. Proteins bound to p13suc1-Sepharose or immunoprecipitated with Cdc2MsA/B antibodies from cells at G1-to-S and G2-to-M phase boundaries showed elevated kinase activities. the Cdc2MsF antibodies separated a G2-to-M phase-related kinase complex. Detection of histone H1 phosphorylation activities in fractions immunoprecipitated with antimitotic cyclin (CyclinMs2) antibodies from G2-to-M phase cells indicates the complex formation between this cyclin and a kinase partner in alfalfa. The observed fluctuation of transcript levels, amounts, and activities of kinases in different cell cycle phases reflects a multilevel regulatory system during cell cycle progression in plants.

Amino Acid Sequence↗
PubMed1996

When the brain changes its mind: interocular grouping during binocular rivalry.

The prevalent view of binocular rivalry holds that it is a competition between the two eyes mediated by reciprocal inhibition among monocular neurons. This view is largely due to the nature of conventional rivalry-inducing stimuli, which are pairs of dissimilar images with coherent patterns within each eye's image. Is it the eye of origin or the coherency of patterns that determines perceptual alternations between coherent percepts in binocular rivalry? We break the coherency of conventional stimuli and replace them by complementary patchworks of intermingled rivalrous images. Can the brain unscramble the pieces of the patchwork arriving from different eyes to obtain coherent percepts? We find that pattern coherency in itself can drive perceptual alternations, and the patchworks are reassembled into coherent forms by most observers. This result is in agreement with recent neurophysiological and psychophysical evidence demonstrating that there is more to binocular rivalry than mere eye competition.

Animals↗
PubMed1996

[Evaluation of complaints and diagnostic methods, considered to be objective, in gastroesophageal reflux].

Authors analyse complaints of 166 patients suffering in gastroesophageal reflux disease, and results of different objective diagnostic methods (X-ray swallowing, endoscopy, 24 hour pH-monitoring, esophageal manometry). The degree of severity of typical complaints and changes found by diagnostic procedures were scored. Individual diagnostic proceduresindicated the characteristic changes of gastroesophageal reflux with great deviations. Hiatal hernia identified by x-ray, esophagitis observed by endoscopy, abnormal reflux revealed by pH-metry together occurred only at 36% of patients. Significant correlation could be revealed only between the degree of changes found by x-ray or pH-metry--applying them one by one--and the complaints of the patients, but with the combination of four diagnostic methods a tight, positive correlation could be demonstrated with the severity of the complaints of the patients in every case. Applying of diagnostic methods as much as possible completing each others, with consideration to the complaints of the patients is suggested for having the diagnosis been precise of the gastroesophageal reflux disease, and for measuring of efficacy of treatment. The importance of tight collaboration of internist, radiologist and surgeon and the significance of complex examination is underlined.

Esophagoscopy↗
PubMed1995

Isolation of a full-length mitotic cyclin cDNA clone CycIIIMs from Medicago sativa: chromosomal mapping and expression.

Cyclins in association with the protein kinase p34cdc2 and related cyclin-dependent protein kinases (cdks) are key regulatory elements in controlling the cell division cycle. Here, we describe the identification and characterization of a full-length cDNA clone of alfalfa mitotic cyclin, termed CycIIIMs. Computer analysis of known plant cyclin gene sequences revealed that this cyclin belongs to the same structural group as the other known partial alfalfa cyclin sequences. Genetic segregation analysis based on DNA-DNA hybridization data showed that the CycIIIMs gene(s) locates in a single chromosomal region on linkage group 5 of the alfalfa genetic map between RFLP markers UO89A and CG13. The assignment of this cyclin to the mitotic cyclin class was based on its cDNA-derived sequence and its differential expression during G2/M cell cycle phase transition of a partially synchronized alfalfa cell culture. Sequence analysis indicated common motifs with both the A- and B-types of mitotic cyclins similarly to the newly described B3-type of animal cyclins.

Amino Acid Sequence↗