Search Results - (Author, Cooperation:Röper)

1615-6102

Springer Online Journal Archives 1860-2000

Biology

Summary Lateral roots ofVicia faba were treated three hours with 0.2 percent caffeine. The ultrastructure of binucleate cells formed that way was studied by electron microscopy. Shortly after the end of treatment, nuclei connected by a strand of nucleoplasm were observed which was referred to nuclear fusions. In binucleate cells no stages reminding of a typical phragmoplast or a cell plate could be identified, whereas wall protrusions occurred at interphase and mitosis, respectively, obviously growing centripetally performing a pseudo-cytokinesis. Some hours later wall formation was more irregular and nuclear constrictions could be observed. Since the microtubules are not affected, the possible effect of caffeine on cytoplasmic streams is discussed.

Electronic Resource

0170-2041

Chemistry ; Organic Chemistry

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

Synthesis of Protected N-Nitroso Sugar Amino Acids.  -  N-(1,3,4,6-Tetra-O-acetyl-2-deoxy-β-D-glucopyranos-2-yl) Amino Acid Methyl Esters and -β-D-galactopyranos-2-yl) Amino Acid Methyl Esters and Their N-Nitroso DerivativesReacting 1,3,4,6-tetra-O-acetyl-β-D-glucosamine hydrochloride (1) or 1,3,4,6-tetra-O-acetyl-β-D-galactosamine hydrochloride (10) with methyl bromocarboxylates in refluxing acetone in the presence of sodium hydrogen carbonate results in the formation of N-(1,3,4,6-tetra-O-acetyl-2-deoxy-β-D-glucopyranos-2-yl) amino acid methyl esters 2-5 and -β-D-galactopyranos-2-yl) amino acid methyl esters 11-12. Nitrosation of these derivatives of sugar amino acids with dinitrogen trioxide in chloroform at 0°C leads to the derivatives of N-nitroso sugar amino acids 6-9 and 13-14.

Durch Umsetzung von 1,3,4,6-Tetra-O-acetyl-β-D-glucosamin-hydrochlorid (1) oder 1,3,4,6-Tetra-O-acetyl-β-D-galactosamin-hydrochlorid (10) mit Bromcarbonsäure-methylestern in siedendem Aceton in Gegenwart von Natriumhydrogencarbonat als Base werden die N-(1,3,4,6-Tetra-O-acetyl-2-desoxy-β-D-glucopyranos-2-yl)aminosäure-methylester 2-5 und -β-D-galactopyranos-2-yl)aminosäure-methylester 11-12 erhalten. Nitrosierung der Zuckeraminosäure-Derivate mit Distickstofftrioxid in Chloroform bei 0°C führt zu den N-Nitroso-Zuckeraminosäure-Derivate 6-9 und 13-14.

1 Ill.

Electronic Resource

0044-8249

Chemistry ; General Chemistry

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

1 Tab.

Electronic Resource

0570-0833

Chemistry ; General Chemistry

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

1 Tab.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The first radial mode of a cylindrical resonator was excited in extracavity and intracavity configurations employing a modulated 3.39 μm HeNe laser. The resonance curves were measured as a function of pressure by a computer-controlled method and fitted to Lorentzian profiles. Measurements were performed for C2H4, CH3Cl, CH3F, C2H6, and CH4, where the optical absorption coefficient determined by transmission experiments increases from C2 H4 to CH4 . From the signal strengths and the Q factors of the resonances the so-called photoacoustic signal (PAS) was determined and compared with theory. Good agreement between theory and experiment was observed for all extracavity measurements and in the case of intracavity experiments with low optical losses in the laser resonator. In order to describe the large discrepancies between the experimentally determined PAS and the existing theory for high losses, improved models were developed, which are based on an inhomogeneous distribution of laser power in the optical cavity. Deviations from these models were found near threshold. The PAS observed above threshold is attributed to amplified spontaneous emission.

Electronic Resource

1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Tobacco seedlings were grown in nutrient agar at a range of ammonium nitrate concentrations either without added sucrose, or with 100 mol m–3 sucrose. In the absence of added sucrose, nitrogen-limited plants had increased levels of glucose, fructose and sucrose, decreased chlorophyll, decreased protein, and decreased Rubisco activity, but the level of the transcript for the small subunit of Rubisco (RbcS) did not decrease compared with nitrogen-sufficient plants. When sucrose was added to nitrogen-sufficient seedlings, there was an increase of sucrose, glucose and fructose in the leaves, growth was increased, and the chlorophyll and protein content, Rubisco activity, and the RbcS transcript level did not change. When sucrose was added to nitrogen-limited seedlings, there was a further increase of sucrose, glucose and fructose, growth was not increased, and there was a further decrease of chlorophyll, protein and Rubisco activity, and a marked decrease of the RbcS transcript level. To check that the decrease of the RbcS transcript level was not an indirect effect due to changes of nitrogen metabolites after adding sugars, glucose was added to Chenopodium cells in the presence and absence of glutamine or azaserine. Changes of glutamine that suffice to increase and decrease the level of the transcript for nitrate reductase (Nia) do not affect the RbcS transcript concentration, and glucose addition still led to a decrease of the RbcS transcript level when the internal glutamine concentration was high. Tobacco seedlings were also grown in nutrient agar at a range of phosphate concentrations either without added sucrose, or with 100 mol m–3 sucrose. Phosphate-limited seedlings did not show a decrease of chlorophyll, protein, Rubisco activity, or the level of the RbcS transcript, compared with phosphate-sufficient seedlings. The addition of sucrose to phosphate-limited plants led to a similar increase of sugars to that seen after adding sucrose to nitrogen-limited seedlings, but did not alter chlorophyll, protein, Rubisco activity, or the level of the RbcS transcript. The addition of sucrose to phosphate-limited plants led to a slight increase of the level of the transcript for nitrate reductase (Nia), increased nitrate reductase activity, and a marked increase of the amino acid content. Phosphate limitation led to an increased level of the transcript for the regulatory subunit of ADP glucose pyrophosphorylase (AgpS2), and this response was strengthened when sucrose was added. The regulation of AgpS2 expression by phosphate and sucrose was further investigated by feeding sucrose and phosphate to detached source leaves via the transpiration stream. The level of the AgpS2 transcript decreased after feeding phosphate and increased after feeding sucrose, and the effect of sucrose was antagonised by phosphate. It is concluded that the response to sugar signalling is modulated by nitrogen and phosphate in a gene-specific manner. The significance of these results for understanding the visual phenotype of nitrogen- and phosphate-limited plants, and the response of photosynthesis and starch synthesis to the plant nutrient status is discussed.

Electronic Resource

1460-9568

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

The study investigated the formation of perforated synapses in rat hippocampal cell cultures. Perforated synapses are defined by their discontinuous postsynaptic densities (PSDs) and are believed to occur in parallel with changes in synaptic activity and possibly also synaptic efficacy. Several in vivo studies have demonstrated an increase in the frequency of perforated synapses induced by development and environmental stimulation as well as long-term potentiation (LTP). Also in in vitro brain slices, LTP was associated with an elevated number of perforated spine synapses. Our study demonstrated for the first time that the formation of perforated synapses can be induced by a short-term increase in spontaneous neural activity in a hippocampal cell culture model. Stimulation with the GABAA-antagonist picrotoxin (PTX) induced a significant increase in the percentage of perforated synapses. This strong increase was blocked when APV was added together with PTX, indicating that the formation of perforated synapses depended on the activation of NMDA receptors. We also showed that inhibition of the tissue type plasminogen activator (tPA-stop/PAI-1) significantly interfered with the activity-induced increase in perforated synapses. This implies that the proteolytic activities of tPA might be involved in steps which are downstream from the NMDA receptor-mediated synaptic plasticity leading to structural changes at synaptic contacts. In contrast, even long-term inhibition of electrical network activity by tetrodotoxin had no effect on the number of perforated synapses, but almost completely abolished the formation of spine synapses. These results indicate that a short-term increase in neural activity via NMDA receptors and a proteolytic cascade involving tPA lead to the formation of perforated synapses.

Electronic Resource

1460-9568

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Hyperpolarization-activated currents (Ih) are key players in shaping rhythmic neuronal activity. Although candidate genes for Ih channels have been cloned (HCN1–HCN4), the subunit composition of different native Ih channels is unknown. We used a combined patch-clamp and qualitative single-cell reverse transcription multiplex polymerase chain reaction (RT-mPCR) approach to analyse HCN1–4 coexpression profiles in four neuronal populations in mouse CNS. Coexpression of HCN2, HCN3 and HCN4 mRNA was detected in single neurons of all four neuronal cell types analysed. In contrast, HCN1 mRNA was detected in neocortical and hippocampal pyramidal neurons but not in dopaminergic midbrain and thalamocortical neurons. HCN1 expression was correlated with significantly faster activation kinetics on the level of individual neurons. Semiquantitative single-cell RT-mPCR analysis demonstrated that HCN1 mRNA expression is at least eightfold higher in cortical neurons than subcortical neurons. We show that single neurons possess complex coexpression patterns of Ih candidate genes. Alternative expression of HCN1 is likely to be an important molecular determinant to generate the different neuronal Ih channel species adapted to tune either subcortical or cortical network activity.

Electronic Resource

1360-0443

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Psychology

This paper reports on an analysis of geographically based data from four communities conducted to evaluate relationships between measures of the physical availability of alcohol and rates of driving after drinking. From a review of the literature, it was expected that rates of driving after dnnking would be directly related to the availability of alcohol at on-premise establishments. Based on theoretical arguments regarding the hfe activities which underlie drinking and driving it was expected that the effects of availability upon these outcomes would extend significantly beyond the local areas of outlets. Taking into account the geographic variations in environmental characteristics (road network density, traffic flow, population density), and socioeconomic (age, gender, race, marital status, income, employment) and drinking characteristics (rates of abstention, frequency and quantity of use) of resident populations, a spatial analysis of drinking driving and alcohol-related crashes was conducted. The results of the analysis showed that physical availability was unrelated to self-reports of driving after drinking and driving while intoxicated and significantly related to rates of single vehicle night-time crashes. In the latter case, physical availability affected both local and adjacent area rates of crashing.

Electronic Resource

1546-1718

Nature Archives 1869 - 2009

Biology

Medicine

[Auszug] Neurodegenerative disorders such as Parkinson and Alzheimer disease cause motor and cognitive dysfunction and belong to a heterogeneous group of common and disabling disorders. Although the complex molecular pathophysiology of neurodegeneration is largely unknown, major advances have been achieved ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] Figure 1 shows the size distribution of G1 and G2 HeLa cell nuclei 5, 60 and 120 min after injection of ruptured HeLa cells into Xenopus eggs. At 5 min, before the nuclei had swollen appreciably, they were all below 17-mm diameter. Also, the distribution of G1 and G2 nuclei between the two size ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] Shaker-related voltage-gated K+ (Kv) channels, are assembled from ion-conducting Kvα subunits, which are integral membrane proteins, and auxiliary Kvβ subunits. This leads to the formation of highly diverse heteromultimeric ...

Electronic Resource

0004-8402

Philosophy

REVIEWS

0022-1910

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Electronic Resource

0024-3841

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Linguistics and Literary Studies

Electronic Resource

1399-3054

Blackwell Publishing Journal Backfiles 1879-2005

Biology

A growth period from day 4 to day 11 after sowing of dark-grown oat seedlings (Avena sativa L. cv. Flämingskrone) was studied. Etioplasts were prepared from various stages. By means of one and two dimensional gel eletrophoresis developmental changes in the polypeptide pattern of the prolamellar body-prothylakoid complex of etioplasts were studied. Polypeptides were described by their molecular weights and pI values after isoelectric focusing. The polypeptide map changes continuously with age, with the onset of effects of senescence around day 7. Concomitantly, proto-chlorophyllide and proteins are degraded, with a higher degradation rate for proto-chlorophyllide. An analysis of protochlorophyllide fluorescence displayed a constant ratio (fluorescence emission at 650 nm/fluorescence emission at 630 nm) from day 6 to day 11. It is concluded, that the best stages for greening studies of dark-grown oat seedlings occur between day 4 and day 6 after sowing.

Electronic Resource

1437-1596

Springer Online Journal Archives 1860-2000

Medicine

Law

Electronic Resource

1437-1596

Springer Online Journal Archives 1860-2000

Medicine

Law

Electronic Resource

1437-1596

Springer Online Journal Archives 1860-2000

Medicine

Law

Electronic Resource

1437-1596

Springer Online Journal Archives 1860-2000

Medicine

Law

Electronic Resource