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H Schnabl

Publications and source records attributed to H Schnabl.

At least 19 recordsLinked to original sources
PubMed2006

Inositol 1,4,5-trisphosphate and Ran expression during simulated and real microgravity.

In order to gain further insight into the signal transduction pathway concerning gravitropism, we studied the expression profiles of mRNA in etiolated sunflower (Helianthus annuus L.) seedlings. Differential-display reverse transcriptase PCR product assayed by capillary electrophoresis revealed the small GTPase Ran, regulating nuclear import and export of proteins. Parallel analysis of inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) release by a highly advanced system of metal-dye detection combined with high-performance liquid chromatography provided evidence that the second messenger Ins(1,4,5)P3 is modulated by changes of the gravity vector. Investigations by fast clinorotation and sounding rockets established a positive correlation between the Ins(1,4,5)P3 level and the expression rate of Ran mRNA during simulated and real microgravity. Since an asymmetric distribution of auxin during graviresponse is suggested to induce differential cell elongation, additional information on the perception and transduction pathways was achieved by auxin stimulation experiments. While we were able to demonstrate an auxin-dependent production of Ins(1,4,5)P3, the expression of Ran mRNA was not affected by auxin. Finally, besides the phosphoinositide system as one element of the signal transduction chain linking graviperception to graviresponse, a Ran-mediated interaction model of extracellular microgravity signal perception and intercellular transduction pathway is proposed.

Chromatography, High Pressure Liquid↗
PubMed2001

Fusicoccin- and light-induced activation and in vivo phosphorylation of phosphoenolpyruvate carboxylase in vicia guard cell protoplasts.

The in vivo regulation of phosphoenolpyruvate carboxylase (PEPCase; EC 4.1.1.31), was studied in purified guard cell protoplasts (GCPs) of Vicia faba L. Incubation of GCPs with fusicoccin (FC) led to the rapid activation of PEPCase and reduced its sensitivity towards the feedback-inhibitor malate. This was accompanied by an increase in the phosphorylation state of the enzyme. Additionally, PEPCase could be transiently activated by white light. Activation and phosphorylation of PEPCase upon illumination were dependent on the presence of potassium in the incubation medium. Treatment of GCPs with inhibitors of H(+)-ATPases, and with abscisic acid (ABA) suppressed the activation of PEPCase in a concentration-dependent manner. Treatment of protoplasts with butyrate also led to PEPCase activation, suggesting a role for the cytosolic pH (pH(cyt)) in the signal transduction process. The presented data indicate that guard cell PEPCase is regulated by reversible phosphorylation of at least one isoform and elucidate first components of the signaling pathway.

Journal Article↗
PubMed1996

Microsomal membrane proteins and vanadate-sensitive ATPase from Vicia faba root tips after clinostat treatment.

Microsomal and soluble protein fractions from Vicia faba root tips were used for SDS-PAGE and Western-immunoblot analysis with anti-ubiquitin antibodies after 9 h clinostat treatment of the plants. In contrast to soluble proteins omnilateral gravistimulation (9 h) resulted in an enhanced proteolytic capacity for microsomal proteins. The increase of vanadate-sensitive ATPase activity was 83% after 9 h clinostat treatment, when the enzyme activity was measured directly after membrane preparation. Enhanced ATPase activity was correlated with the appearance of a polypeptide of about 100 kDa and its fragments (93 and 80 kDa). ATPases are not the only membrane bound proteins, which are changed during clinostat treatment, as several ubiquitinated polypeptides were also affected. A 1 h storage of microsomal fractions led to a shift of band intensities on ubiquitin-specific Western-blots. The demonstrated effect could not be observed, when fractions were isolated in the presence of protease inhibitors. In accordance with the polypeptide analysis omnilateral gravistimulation resulted in an enhanced capacity to degrade specific microsomal ubiquitin-conjugates, whereas the soluble ubiquitin-pool was not visibly affected.

Adenosine Triphosphatases↗
PubMed1996

Effects of fast clinostat treatment and microgravity on Vicia faba L. mesophyll cell protoplast ubiquitin pools and actin isoforms.

With parabolic rocket flights and fast clinostat treatments, the effect of microgravity on ubiquitin, ubiquitin-protein conjugates, and actin isoforms of Vicia faba mesophyll protoplasts was studied. Western immunoblotting with ubiquitin antibodies revealed that simulated and particularly, real microgravity influenced the amount of free ubiquitin and of 18, 19, and 40 kD ubiquitin conjugates by inducing strong oscillations in the proteins concentrations over time. Simulated microgravity and microgravity-phase during parabolic rocket flights resulted in a decrease of actin isoforms. Results obtained support the assumption, that microgravity and fast clinostat treatment have a direct effect on Vicia faba mesophyll protoplast metabolic activities.

Actins↗
PubMed1995

Electrofusion of plant cell protoplasts under microgravity--a D-2 spacelab experiment.

Plant cell protoplasts, derived from sexually incompatible plant species, have proved to be a good system for somatic hybridization by electrofusion. Under microgravity, an increase in fusion yield can be expected, especially if the parental cells differ markedly in size or specific density. On the D-2 spacelab mission flown in 1993, electrofusion experiments were performed with three different objects, i.e. tobacco as model system, Helianthus as an important crop, and Digitalis as a plant of pharmacological interest. The resulting fusion products were cultivated (along with parental cells) for 10 days under microgravity, and subsequently regenerated on ground for biochemical analysis. Results are presented on the observation of the fusion process during flight, heterofusion yields, ultrastructural investigation of fusion products immediately after fusion, and characterization of the resulting hybrids. The results are interpreted on the background of earlier microgravity-experiments on sounding rockets or parabolic flights.

Cardenolides↗
PubMed1994

Selection and enrichment of differentially labeled plant protoplasts.

A fast and efficient method for the selection of plasmamembrane-marked protoplasts via magnetic-associated cell separation (MACS) was developed. Isolated mesophyll protoplasts from sunflower (Helianthus annuus L.) were covalently labeled at their plasma membrane with fluoresceine isothiocyanate (FITC) with an efficiency of greater than 95%. They were subsequently coupled to specific monoclonal antibodies against FITC, which were conjugated to magnetic beads, and mixed with unlabeled hypocotyl protoplasts. About 95% of the marked mesophyll protoplasts were separated by the MACS system with a purity of greater than 80%. Protoplasts embedded in agarose showed normal dividing activities.

Antibodies, Monoclonal↗
PubMed1993

Purification of phosphoenolpyruvate carboxylase subunits and isoforms from Vicia faba L. by preparative gel electrophoresis and their detection by enzyme-linked immunosorbent assay.

A purification procedure which yields nearly homogenous subunits of stomatal phosphoenolpyruvate carboxylase from epidermal strips of Vicia faba L. is reported. Preparative gel electrophoresis was found to be the most suitable technique for subunit purification. Denatured subunits of the stomatal enzyme in the eluate were immunologically detected by enzyme-linked immunosorbent assay (ELISA) tests. The enzyme preparation meets all requirements for its use in antibody production.

Electrophoresis, Polyacrylamide Gel↗
PubMed1989

[Hepatitis contagiosa canis (H.c.c.)--2 cases in Austria].

Two cases of H.c.c. which occurred in winter 1987 in Vienna are described. Case one was a female Chow-Chow, 8 weeks of age, that died from the peracute form of the disease. The diagnosis was confirmed by histology and direct immunofluorescence. Case two, a 9-month old female Kuvacz, showed clinical signs of the subacute form of H.c.c. She was hospitalized and therapy was successful. The disease was diagnosed by the typical clinical signs and the raise of antibodies in paired serum samples. Etiology, clinical signs and immunology of H.c.c. are discussed.

Adenoviruses, Canine↗
PubMed1980

Immobilisation and mechanical, support of individual protoplasts.

Mesophyl cell protoplasts of Vicia faba were suspended in a solution consisting of 10% sodium alginate and 0.4 M mannitol. The protoplasts could be immobilized by cross-linking the alginate in the presence of 100 mM CaCl2. Changes in the osmolarity of the external medium led to reversible shrinkage and swelling of the entrapped protoplasts. It was demonstrated by using the pressure probe technique that a pressure gradient (cell turgor pressure) of several 100 mbar is built up when the immobilized cells were transferred to hypotonic solution. By complexing the Ca2+ in the alginate matrix with sodium citrate buffer the protoplasts could be released from the matrix. No morphological change or alteration of the membrane permeability of the immobilized protoplasts was observed after a storage period of up to 14 days at 4 degrees C in the matrix.

Alginates↗
PubMed1980

Does removal of hydrogen change the electron energy-loss spectra of DNA bases?

Quantum-chemical calculations using the CNDO/2 method are applied to radicals produced by cleaving hydrogen from the DNA bases adenine, guanine, cytosine, and thymine. The resulting sequences of occupied molecular orbitals show that the loss of hydrogen atom in most cases leads to the loss of one phi electron. Consequently the phi electron part of the energy-loss spectra will change considerably. In view of this, it is possible that the change of the electron energy-loss spectra due to irradiation, as observed by Isaacson et al., might be caused by the loss of hydrogen atoms. Such damage does not influence the electron-microscopical image appreciably, as long as no deleterious secondary processes are initiated.

DNA↗
PubMed1980

Potassium Chloride as Stomatal Osmoticum in Allium cepa L., a Species Devoid of Starch in Guard Cells.

K(+) and Cl(-) contents of guard cells and of ordinary epidermal cells were determined in epidermal samples of Allium cepa L. by electron probe microanalysis; malate contents of the same samples were determined by enzymic oxidation. KCl was, in general, the major osmoticum in guard cells, irrespective of whether stomata had opened on leaves or in epidermal strips floating on solutions. The solute requirement varied between 50 and 110 femtomoles KCl per micrometer increase in aperture per pair of guard cells. Stomata did not open on solutions of K iminodiacetate, presumably because its anion could not be taken up. Stomata opened if KCl or KBr was provided. Taken together, the results indicate that the absence of starch from guard cells deprived them of the ability to produce malate in amounts of osmotic consequence and that the presence of absorbable Cl(-) (or Br(-)) was necessary for stomatal opening.Previous nutrient supply of the plants determined whether the charges of K(+) in guard cells were completely balanced by Cl(-) or only partially. Addition of K(2)SO(4) to the nutrient solution reduced the participation of Cl(-) in stomatal ion transfer, even if epidermal strips of these plants were later exposed to KCl solution. The anion supplying the charge complement in these cases is not known.Although malate appeared not to participate in stomatal ion transfer in onion, epidermal samples of this species did contain malate. Malate accumulated in the epidermis of leaves put into the light but disappeared from illuminated epidermal strips floating on solutions. In whole leaves, epidermal malate content was positively correlated with stomatal opening; in epidermal strips floating on solutions, the correlation was negative or absent.

Journal Article↗
PubMed1978

Availability of Chloride Affects the Balance between Potassium Chloride and Potassium Malate in Guard Cells of Vicia faba L.

Electron probe microanalysis for K and Cl and enzymic determination of malate were performed on epidermal strips of Vicia faba L. which had been incubated with 0.1 equivalent of K(+) per liter in the absence or presence of Cl(-). In the absence of Cl(-), iminodiacetate, a presumed impermeant zwitterion, served as anion. With no Cl(-) in the medium, 91% of the K(+) imported into the guard cells during stomatal opening was neutralized by malate production; import of Cl(-) (presumably from the rest of the epidermal tissue) contributed 6%. In the presence of Cl(-), 50% of the necessary negative charges were provided by malate synthesis, 45% by Cl(-) import. Stomatal opening was not obviously affected by the chloride concentration in the incubation medium, but malate production declined roughly linearly with the logarithm of [Cl(-)] between 10(-5) and 10(-1) equivalent per liter.

Journal Article↗