Die Kinetik der Ionenaufnahme durch junge und alte Sprosse von Mnium cuspidatum

Zusammenfassung Die Kinetik der Ionenaufnahme durch junge und alte Sprosse von Mnium cuspidatum wurde untersucht. Die verschieden alten Sprosse unterscheiden sich vor allem durch das Vorhandensein einer aktiven Gipfelknospe bei den jungen Gametophyten, die bei den alten offenbar ihre Tätigkeit eingestellt hat. Im niedrigen Konzentrationsbereich (0–0,5 mM) haben jungen und alte Sprosse hyperbolische Isothermen der Ionenaufnahme, die sich etwas hinsichtlich der apparenten Michaeliskonstanten und der Maximalgeschwindigkeit unterscheiden. Im hohen Konzentrationsbereich (1–10 mM) ist der Unterschied qualitativ. Mit jungen Sprossen erhält man eine lineare oder exponentielle Isotherme, mit alten Sprossen eine hyperbolische Kurve. Der vermutete Einfluß der Gipfelknospe kann mit Effekten von Wuchsstoffen auf den Stofftransport zusammenhängen und läßt einen Einfluß dieser Regulationssysteme auf die Membranfunktion vermuten.

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The kinetics of ion uptake by young and old branches of mnium cuspidatum

Summary Isotherms of K(Rb)-, Cl- and SO₄-uptake by young and old branches of the moss Mnium cuspidatum were investigated. Old moss gametophytes from the 1966 vegetation period were collected in the forests surrounding Darmstadt from February to mid-April 1967 and from the 1967 season in late September 1967. Young plants were sampled from mid-April to the end of May 1967 and they were also grown by water culture of old plants.Both young and old branches have hyperbolic isotherms of ion uptake in the low concentration range (0–0.5 mM) (Fig. 1–3), which slightly differ in K _mand V _max (Table). Isotherms in the high range (1–10 mM), however, are drastically different, changing from linear or exponential with young moss branches to hyperbolic with old gametophytes (Figs. 1–3).The linear or exponential high-range isotherm obtained with young moss plants is compared with other examples reported in the literature (Fig. 4). As the leaflets of the moss plants, which constitute 2/3 of the fresh weight of the material used in the experiments, have well developed vacuoles, the correlation between hyperbolic isotherms and vacuolation does not apply here (Fig. 4a, Torii and Laties, 1966).The change in shape of the high-range moss isotherm with age resembles the change from exponential to hyperbolic kinetics in isolated potato discs during washing (Fig. 4b, Laties, Macdonald and Dainty, 1964). The events triggered by isolation of potato discs from the interior of the tuber may be similar to the changes in the moss material under the control of the terminal bud, which is only active in the young branches.The suggested influence of the active terminal bud of young moss plants on the ion absorption process of cells in the tissue may be related to effects of growth substances on translocation reported in the literature and may point to a direct effect of these regulatory systems on membrane function.In this respect the comparison of corn root stele and cortex is of interest. Isolated steles, both freshly isolated and after washing, have exponential isotherms in the high range (Fig. 4c), whereas cortex displays a hyperbolic isotherm which changes little with ageing (Lüttge and Laties, 1967). In contrast to the case in potato and moss materials, this phenomenon is not simply due to ageing but involves morphogenetic differences.Temperature is another factor which influences the shape of the high range isotherm. All examples discussed so far refer to experiments at room temperature. At low temperatures high-range isotherms for proximal root tissue or aged potato discs have an exponential shape (Torii and Laties, 1966; Laties, Macdonald and Dainty, 1964). It thus appears that the exponential isotherm of young moss branches indicates that as in freshly isolated potato discs or in corn root stele the metabolic high-range uptake system is not developed.

     

Electrophoretic studies of muscle proteins. I. Complex formation between delta protein and F-actin

Complex formation between delta protein and F-actin has been demonstrated by electrophoretic technique. The high turbidity of F-actin solutions has made it necessary to work at low concentrations of this protein (0.8 to 1.6 mg/ml). Delta protein concentrations were four to six times greater. At higher concentrations all F-actin was bound to delta protein, on both limbs. The combination ratio was about 1:1 by weight. We call this complex “delta-actin.” When the complex formed there was a slight fall in viscosity, indicating side-by-side union, but the turbidity greatly increased. The mobility of delta-actin was always less than that of free F-actin and sometimes also less than that of free delta protein. We earlier reported that delta protein is probably a polymer of tropomyosin. Its sedimentation constant (4.4 to 6.0 S) is higher than the of any other form of tropomyosin so far described. It may be the native molecule, its structure preserved by our relatively simple method of extraction and purification. The filaments of the I band may be composed of delta-actin. Since delta protein also forms a complex with myosin the filaments of the A band may be composed of delta-myosin. Delta protein may be a structural component which, in addition to other activities, may direct the building of both filament arrays and strengthen them.     

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Rate of erythropoietin formation in humans in response to acute hypobaric hypoxia

This study was carried out to investigate the early changes in erythropoietin (EPO) formation in humans in response to hypoxia. Six volunteers were exposed to simulated altitudes of 3,000 and 4,000 m in a decompression chamber for 5.5 h. EPO was measured by radioimmunoassay in serum samples withdrawn every 30 min during altitude exposure and also in two subjects after termination of hypoxia (4,000 m). EPO levels during hypoxia were significantly elevated after 114 and 84 min (3,000 and 4,000 m), rising thereafter continuously for the period investigated. Mean values increased from 16.0 to 22.5 mU/ml (3,000 m) and from 16.7 to 28.0 mU/ml (4,000 m). This rise in EPO levels corresponds to 1.8-fold (3,000 m) and 3.0-fold (4,000 m) increases in the calculated production rate of the hormone. After termination of hypoxia, EPO levels continued to rise for approximately 1.5 h and after 3 h declined exponentially with an average half-life time of 5.2 h.     

Ploidy and morphology in osteosarcoma

In a cytometric DNA study of high-grade osteosarcoma, the relationship between DNA content and morphology was analyzed. The investigation, based on microspectrophotometry of tissue sections and flow cytometry (FCM), included both primary lesions and recurrences. FCM analysis, applied to a consecutive series of 47 primary osteosarcomas, disclosed that 2 were diploid and 45 were nondiploid, 8 of which were tetraploid. Multiple aneuploid peaks were detected in 13 tumors. Among the nondiploid tumors, there was no clear relationship between the peak DNA value(s) and the histologic subtype (osteoblastic, chondroblastic, fibroblastic) or grade (III-IV). The proliferative activity, as reflected by the percentage of S-phase cells, could be determined in 38 of the 47 tumors analyzed by FCM. The percentage was higher for aneuploid than for tetraploid lesions; however, the distribution of S-phase cells was not related to the histologic subtype or the grade of the tumors. To assess the reliability of a single sample for FCM, the DNA content of biopsy and surgical specimens was compared in 20 tumors; there was complete agreement in all cases with respect to the classification of the lesion as diploid, tetraploid or aneuploid. Analysis by FCM or microspectrophotometry of 12 local recurrences and 16 metastases and the corresponding 19 primary tumors showed that an aneuploid characteristic of the primary lesion was retained during progression of the disease. In 12 tumors analyzed by microspectrophotometry in tissue sections, comparison of chondroblastic and osteoblastic/fibroblastic areas within the same lesion consistently disclosed hyperploidy in both areas.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of nucleosome distortion on the linking deficiency in relaxed minichromosomes

The wrapping of closed circular DNA on a protein surface, followed by relaxation with a topoisomerase and removal of proteins, produces a characteristic DNA linking deficiency, delta Lk. We show that the magnitude of delta Lk depends upon the surface shape, and we calculate changes in delta Lk caused by particular distortions of the protein wrapping surface. If the DNA remains attached to the surface during distortion, the DNA winding number, phi, is not altered. The change in delta Lk is then equal to the change in the surface linking number, SLk, which is a straightforward measure of the wrapping of the DNA around the surface. For left-handed wrapping, as in a nucleosome, SLk = -n, the number of times that the DNA axis winds around the axis of the protein complex. We calculate values of SLk for the helical wrapping of a constant length of DNA on protein surfaces having the shapes of cylinders and of ellipsoids and hyperboloids of revolution. If the equatorial radius of the protein is fixed, change in shape from a cylinder to a hyperboloid increases SLk, while the corresponding change to an ellipsoid reduces SLk. We apply the general results to the interpretation of experiments in which minichromosomes are relaxed with topoisomerase at various temperatures and delta Lk is determined. The result is that a distortion of the nucleosome core by at most 5% (the change in the radius at the axial extremity relative to the equator) is sufficient to explain the observed delta Lk changes.     

Rhizobium meliloti exopolysaccharide Mutants Elicit Feedback Regulation of Nodule Formation in Alfalfa

Nodule formation by wild-type Rhizobium meliloti is strongly suppressed in younger parts of alfalfa (Medicago sativum L.) root systems as a feedback response to development of the first nodules (G Caetano-Anollés, WD Bauer [1988] Planta 175: 546-557). Mutants of R. meliloti deficient in exopolysaccharide synthesis can induce the formation of organized nodular structures (pseudonodules) on alfalfa roots but are defective in their ability to invade and multiply within host tissues. The formation of empty pseudonodules by exo mutants was found to elicit a feedback suppression of nodule formation similar to that elicited by the wild-type bacteria. Inoculation of an exo mutant onto one side of a split-root system 24 hours before inoculation of the second side with wild-type cells suppressed wild-type nodule formation on the second side in proportion to the extent of pseudonodule formation by the exo mutants. The formation of pseudonodules is thus sufficient to elicit systemic feedback control of nodulation in the host root system: infection thread development and internal proliferation of the bacteria are not required for elicitation of feedback. Pseudonodule formation by the exo mutants was found to be strongly suppressed in split-root systems by prior inoculation on the opposite side with the wild type. Thus, feedback control elicited by the wild-type inhibits Rhizobium-induced redifferentiation of host root cells.     

Chemotaxis,induced gene expression and competitiveness in the rhizosphere

Rhizobia are soil bacteria which symbiotically infect legume roots and generate nodules in which they fix atmospheric nitrogen for the plant in exchange for photosynthetically fixed carbon. A crucial aspect of signal exchange between these symbionts is the secretion of phenolic compounds by the host root which induce nodulation gene expression in the bacteria. Stimulation of nod gene expression by host phenolics is required for nodule formation, is biochemically specific at 10^-6 M, and is mediated by nodD. We and others have shown that rhizobia display chemotaxis to 10^-9 M of the same phenolic compounds. Chemotaxis to inducer phenolics is selectively reduced or abolished by mutations in certain nod genes governing nodulation efficiency or host specificity. Conversely, mutations in rhizobia that affect general motility or chemotaxis have substantial effects on nodulation efficiency and competitiveness. These findings suggest that microbes entering the rhizosphere environment may utilize minor, non-nutrient components in root exudates as signals to guide their movement towards the root surface and elicit changes in gene expression appropriate to this environment.     

Comparison of gene expression of extracellular matrix molecules in brain microvascular endothelial cells and astrocytes.

By use of random-primed cDNA probes the expression of extracellular matrix molecules in cerebral microvascular endothelial cells (cEC) and in astrocytes from mouse brain was examined. Two phenotypically different batches of cloned cEC were used. Expression of major adhesive ECM molecules, constituting the endothelial basement membrane (i.e., fibronectin, laminin A, B and collagen IV) and of other attachment factors, such as SPARC (osteonectin), tenascin and thrombospondin 1, was examined. We have demonstrated that cEC of different morphology display variations in the expression of fibronectin (FN), thrombospondin 1 (TSP1) and collagen IV (C IV). Astrocytes were shown to contain FN, TSP1, TN and SPARC mRNA. Unexpectedly, SPARC mRNA could not be detected in any of the capillary endothelial cells examined. Therefore, we suggest that astrocytes are likely to be involved in endothelial differentiation and function in the central nervous system via ECM molecule secretion.