Showing papers by "University of Freiburg published in 1973"

1-N-naphthylphthalamic acid and 2,3,5-triiodobenzoic acid : In-vitro binding to particulate cell fractions and action on auxin transport in corn coleoptiles.

Abstract: Auxin transport in corn coleoptile sections was inhibited by 2,3,5-triiodobenzoic acid (TIBA) as well as by 1-N-naphthylphthalamic acid (NPA); this inhibition was effected within 1 min of application.A particulate cell fraction-presumably plasma-membrane vesicles-specifically binds NPA and properties of these binding sites were studied using (3)H-NPA and a pelletting technique. The saturation kinetics of the physiological NPA effect, i.e. the inhibition of auxin transport, is similar to that of the specific in-vitro NPA binding. Half saturation of the inhibitory effect was found with about 5×10(-7) M TIBA and with 10(-7) M NPA. Both substances also decreased the speed of movement of auxin pulses within coleoptile sections.NPA dissociates from its binding site when the particulate cell material is centrifuged through an NPA-free cushion. The NPA that is washed from its binding site can be used in another binding test without any apparent change and is chromatographically unaltered. Therefore, the NPA binding is probably reversible and non-covalent. Inhibition of auxin transport by TIBA or NPA could also be reversed when the coleoptile sections were washed in buffer.The movement of (131)I-TIBA in corn coleoptiles appears to be polar in a basipetal direction. Higher concentrations of indoleacetic acid or TIBA inhibited this polar movement, suggesting that TIBA moves in the same channels as auxin. With (3)H-NPA, however, no polar transport could be detected. Together with the in-vitro binding results, these data indicate that TIBA acts directly at the auxin receptor while NPA has a different receptor site.The effect of TIBA and NPA on elongation, with or without auxin, is neglegible in comparison to their effects on auxin transport.

Selective inhibition of the transmembrane Ca conductivity of mammalian myocardial fibres by Ni, Co and Mn ions.

Abstract: According to earlier studies on mammalian papillary muscles, Ni and Co ions reduce the Ca dependent mechanical response whilst the action potential persists. In order to clarify the mode of action of these cations together with those of Mn their effects on the transmembrane fast Na and of the slow Ca currents were studied in voltage clamp experiments using the double sucrose gap technique. By a conditioning clamping procedure the Ca current was separated from the Na current. The following results were obtained: 1. Ni ions (2 mM) and Co ions (2 mM) strongly depress the Ca conductivity of the membrane. The same blockade was observed under the influence of Mn ions (2 mM). Even in the continued presence of Ni, Co or Mn the transmembrane Ca conductivity can be restored to a varying degree by increasing the extracellular Ca concentration. 2. In contrast to this strong inhibitory effect on the transmembrane Ca inward movements the fast transient Na current is only slightly affected if at all. 3. Apart from their selective inhibitory action on the transmembrane Ca current, Co ions show some additional features a) enhancement of its inhibitory action by repeated membrane depolarizations. b) Co-induced replacement of the slow Ca inward current by a transitory fast inward current component, c) synergetic effects of Co with Ca in restricting the fast Na current. 4. The selective inhibition of the transmembrane Ca conductivity clearly demonstrates the existence of a separate channel for Ca which is independent from the fast Na channel of the membrane.

Direct evidence for a colchicine-induced impairment in the mobility of membrane components.

Abstract: Freeze-etch electron microscopy was used to show that colchicine interacts with membranes of the ciliate protozoan Tetrahymena pyriformis. Colchicine impairs the temperature-induced translational and vertical mobility of the membrane-intercalating particles of the freeze-fractured alveolar membranes lying just below the plasma membranes.

Optokinetic motion sickness and pseudo-Coriolis effects induced by moving visual stimuli.

Abstract: Pseudo-Coriolis effects (PCE) and optokinetic motion sickness are elicited by bending the head out of the axis of rotation of a circular visual surround when that moving surround induces the illusi...

Particle-bound phytochrome from maize and pumpkin.

Abstract: PHYTOCHROME-induced changes in membrane properties have been inferred from physiological studies for some time1–7. Hendricks and Borthwick6 have proposed that the primary action of phytochrome is indeed the induction of such membrane changes and Smith7 has proposed a mechanism for phytochrome-membrane interaction. The interest in a search for evidence of a direct association between phytochrome and cellular membranes has therefore been considerable. The polarotropic response of Dryopteris8, chloroplast movement in Mougeotia9 and the photoconversion of phytochrome in corn coleoptiles in polarized light10 have all been taken to indicate that at least some phytochrome is located and orientated in the periphery of the cytoplasm or the plasmalemma itself. An immunological approach has been attempted11 and Ptr-induced changes in black lipid membrane permeability have recently been reported12 (Pr and Ptr are the two photo-reversible forms of phytochrome). Rubinstein et al.13 reported that about 4% of the total extractable phytochrome from Avena could be pelleted at 40,000g from a 1,500g supernatant, pH 7.4. Here we report the presence of particle-bound phytochrome in extracts from maize coleoptiles and pumpkin hooks and suggest a mechanism for the interaction of the pigment with its binding site(s).

Commitment to meiosis in fission yeast

Abstract: Mutants of Schizosaccharomyces pombe blocked during meiosis were analysed with respect to the induction of diploid mitotic division. Wild type zygotes of this yeast can form diploid colonies with a low probability (ca. 1%) when they are transferred to fresh growth medium. Mutants of three genes affecting meiosis responded to the shift by forming diploid colonies with high yield (ca. 80% of the zygotes). Hence, commitment to meiosis could not be reached by such zygotes. Zygotes of a fourth meiosis-I-deficient mutant were unable to yield diploid colonies more effectively than wild type zygotes. Morphological changes were prominent in the mutant zygotes not reaching commitment (as well as in mutant cells that could not complete conjugation), indicating that activities needed during early stages of conjugation were not turned off in these zygotes.

Enzymic activities and galactomannan mobilisation in germinating seeds of fenugreek (Trigonella fœnum-graecum L. Leguminosae) : Secretion of α-galactosidase and β-mannosidase by the aleurone layer.

Abstract: The activities of α-galactosidase, β-mannosidase and α-mannosidase were determined in extracts from the endosperm and from the embryo of fenugreek seeds at different stages of germination. Endosperm homogenates contained little or no activity of the above enzymes in the early stages of germination, before the reserve galactomannan began to be mobilised. The onset of galactomannan breakdown coincided with the appearance of α-galactosidase and β-mannosidase activities, which increased throughout the period of galactomannan degradation and then remained constant. A similar rise in α-galactosidase and β-mannosidase activities occurred during galactomannan breakdown in dry-isolated endosperms incubated under germination conditions. The increase could be suppressed by metabolic inhibitors which also inhibit galactomannan breakdown. Embryo homogenates contained high α-galactosidase, high α-mannosidase and some β-mannosidase activity at all stages of germination. No “oligomannosyl β-1,4 phosphorylase” activity could be detected either in the endosperm or in the embryo. It is concluded that the galactomannan of fenugreek is broken down by a series of hydrolases secreted by the aleurone layer of the endosperm. They include α-galactosidase, β-mannosidase and probably also endo-β-mannanase.

Turnover of Phytochrome in Pumpkin Cotyledons

Abstract: By using density labeling, it was found that the protein moiety of phytochrome is synthesized de novo in the red-absorbing form in cotyledons of dark-grown pumpkin (Cucurbita pepo L.) seedlings, as well as those irradiated with red light and returned to the dark. The rate of synthesis appears to be unaffected by the light treatment. Turnover of the red-absorbing form was also detected in dark grown seedlings using density labeling, while turnover of the far red-absorbing form is already implied from the well known "destruction" observed in irradiated seedlings. In both cases, true degradation of the protein is involved, but the rate constant of degradation of the far red-absorbing form may be up to two orders of magnitude greater than that of the red-absorbing form. The data indicate that, in pumpkin cotyledons, phytochrome levels are regulated against a background of continuous synthesis through divergent rate constants of degradation of the red and far red-absorbing forms and the relative proportions of the two forms present.

Calcium-mediated action potentials in mammalian myocardium

Abstract: Cat papillary muscles were depolarized by raising the external K concentration so that resting potential went from about −80 mV to −50 mV. This caused inactivation of the transmembrane Na system. The remaining Ca-mediated action potentials showed greater overshoot, reduced upstroke velocity and action potential duration, and higher threshold of excitation. A graded electrical response to stimulous strength was also present. These action potentials depended mainly on the extracellular Ca concentration [16]. Further, the specific Ca-antagonistic compounds verapamil and D 600 [10] or Ca-with-drawal completely abolished the ability of the K-depolarized fibres to respond to stimulation with propagated electrical activity. Conversely, extra Ca, epinephrine or isoproterenol overcame this inhibitory effect by increasing the Ca transmembrane influx. Also, within 1 min after returning treated muscles to normal K 0 Tyrode solution, the Na system was reactivated and apparently normal electrical activity possible. In this case, Ca-withdrawal and the Ca-antagonists lose their electrical inhibitory influence, while excitation-contraction uncoupling still persist.

Evidence of non-specificity of the Ca channel in mammalian myocardial fibre membranes. Substitution of Ca by Sr, Ba or Mg as charge carriers.

Abstract: In order to study the influence of Sr, Ba and Mg ions upon the transmembrane slow inward current, voltage clamp experiments using the double sucrose gap technique were performed on isolated ventricular trabeculae of cats. The separation of the slow inward current (mainly carried by Ca under “physiological” conditions) from the fast Na current was achieved by use of the conditioning clamp technique. The results show, that in addition to Ca as the main “physiological” charge carrier, Sr, Ba and Mg ions can act as charge carriers for the slow inward current. This clearly proves the non-specificity of the slow membrane channel for Ca in the mammalian ventricular myocardium.

Morphological observations on the contact-induced lysis of target cells.

Abstract: Interactions in tissue culture of sensitized C57BL spleen and DBA/2 mastocytoma cells have been studied by microcinematography, electronmicroscopy and light microscopy. Motile lymphocytes with their characteristic hand mirror shape move on the surface membrane of the target cells, establishing a close contact within a few minutes. As seen by electron microscopy and equidensitometry, the contact between the cells is very firm, leading to damage of the target cell membrane while leaving the effector cell intact. Analysis of time-lapse cinematography shows that one motile lymphocyte has the capacity to lyse more than one target cell, a phenomenon which may account for the highly efficient surveillance mechanism in vivo. The role of soluble factors and the importance of the lymphocytic uropod in cellular interactions are discussed.

π‐Orbital‐Wechselwirkungen „through space”︁ und „through bond”︁ in Tricyclo[4.2.0.0]octadienen

Abstract: Die vier ersten Banden im Photoelektronenspektrum des anti- und des syn-Tricyclo[4.2.0.02.5]-octadiens (2 bzw. 3) werden, unter Verwendung des Konzepts der „through space”- und „through bond”-Wechselwirkung zwischen den beiden Basis-π-Orbitalen, bestimmten Molekulorbitalen zugeordnet. Wegen der unterschiedlichen Konfiguration von 2 und 3 lassen sich im vorliegenden Fall die beiden Wechselwirkungstypen trennen. Sowohl in 2 als auch uberraschenderweise in 3 dominiert die „through bond”-Wechselwirkung, so das in beiden Fallen die symmetrische Linearkombination π+ der π+-Orbitale (in 2 bezuglich der zweizahligen Achse, in 3 bezuglich der Spiegelebene) energetisch uber der antisymmetrischen Kombination π− zu liegen kommt. Die Energiedifferenz e(π+) – e(π−) betragt in 2 0.97 eV, in 3 0.36 eV. π-Orbital Interaction „Through Space” and „Through Bond” in Tricyclo[4.2.0.02,5]octadienes The first four bands in the photoelectron spectra of anti- and syn-tricyclo[4.2.0.02,5]octadiene (2 and 3, respectively) have been assigned to specific molecular orbitals. This assignment is based on the concept of „through space” and „through bond”( interaction between the two basis π-orbitals. Because of the different configurations of 2 and 3 it is possible to separate the two types of interactions. In both cases the „through bond” interaction dominates. As a result the symmetric linear combination π+ (symmetric with respect to the twofold rotation axis in 2 or the plane of symmetry in 3) lies above the antisymmetric combination π−. The orbital energy differences e(π+) – e(π−) are 0.97 eV in 2 and 0.36 eV in 3.

Structural organization of the transcription of ribosomal DNA in oocytes of the house cricket.

Abstract: The DNA molecules which contain the cistrons for ribosomal RNA (rDNA) consist of repeats of alternating segments of (i) regions which are transcribed into the primary rRNA precursors (pre-rRNA) and (ii) regions which are either not transcribed (corresponding to “spacers” sensu Miller and Beatty1) or might be, perhaps in parts, transcribed into RNA molecules which, however, are not covalently. linked with pre-rRNA (“spacers” sensu Reeder and Brown2 ; for demonstration of partial transcripts from spacers see Scheer et al.3). The relative arrangement of the “spacer” units and the stretches coding for pre-rRNA (corresponding to the matrix units of Miller and Beatty1,4) has been elucidated by different methods in chromosomal and extrachromosomal rDNA of diverse amphibian species, including urodeles and anurans1,3–13. In the clawed toads, Xenopus laevis and X. muelleri, according to differential DNA denaturation studies12,13, this pattern of arrangement is identical in both chromosomal (“nucleolus organizer”) and extrachromosomal (“amplified”) rDNA. Extrachromosomal nucleolar material consisting of the actively transcribing amplified rDNA is especially suitable for biochemical and electron microscopic studies because it provides a natural enrichment of this kind of DNA in a state which is topologically isolated from all the other chromatin. We have therefore chosen, in order to examine the generality of the organization of transcribing rDNA, another amplified rDNA system, the extrachromosomal DNA masses which occur in the oocytes of diverse insects and constitute a considerable amount of the total nuclear DNA (for example, 59% in Tipula oleracea14, 23–35% in Dytiscid beetles15 and 14–31% in Acheta domesticus 16–19 ). As has been shown by numerous authors18,20–24 a favourable material in this respect is the house cricket, A. domesticus.

Release of prostaglandins from isolated cat spleen by angiotensin and vasopressin.

Abstract: Isolated perfused cat spleens release prostaglandins E and F in response to the injection of angiotensin, an agent which produces contraction of vascular and capsular smooth muscle. The injection of vasopressin, which acts exclusively on the vasculature, releases only prostaglandin E. The release of all prostaglandins is abolished by perfusion of the spleen with 2 μg/ml indomethacin. After inhibition of synthesis and, consequently, of release of prostaglandins vascular responses to both angiotensin and vasopressin and capsular responses to angiotensin are augmented. The results support the hypothesis of prostaglandins as modulators of hormone effects.

Genes involved in mating type expression of fission yeast.

Abstract: Mutations of Schizosaccharomyces pombe are described, which change homothallism to heterothallism without affecting the mating type locus itself The genetic block was effective at the level of agglutinated cells in two instances, or before that in two other cases Mutations of particular interest affected meiosis as well, when homozygous diploid strains were constructed In these strains azygotic meiosis was inducible by the addition of h + cells, even in the absence of cellular fusion