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31.
32.
The high-affinity uptake system of phosphatelimited cyanobacterium Anacystis nidulans [Synechococcus leopoliensis (Raciborski) Komarek] is characterized by a threshold value below which uptake cannot occur. Here it is shown that, if phosphate-limited cyanobacteria are challenged with a short pulse of high phosphate concentration that appreciably exceeds this threshold value, the uptake system undergoes an adaptive response, leading to the attainment of new kinetic properties and a new threshold value. These new properties are maintained for several hours after the pulse. A notable characteristic of this new state is a wide linear dependence of the uptake rate on the external phosphate potential that is a function of the driving force of the uptake process. According to theoretical arguments it is shown that this “linear operation mode” can be explained by the simultaneous operation of several uptake systems with different, staggered threshold values and kinetic properties. Moreover, the new linear uptake properties, in turn, reflect the prehistory of phosphate supply experienced by the population. The consequences of this result with regard to environmental fluctuations of the phosphate concentration in lakes are discussed. 相似文献
33.
Gernot Falkner Ferdinand Wagner John Victor Small Renate Falkner 《Journal of phycology》1995,31(5):745-753
The blue-green alga Anacystis nidulans Drouet (Synechococcus leopoliensis Raciborski) cultivated under phosphate-limited conditions adopts a threshold value in the nanomolar range below which uptake ceases. In this study, we investigated the influence of phosphate pulses on the regulation of uptake behavior during reestablishment of the threshold value. Short-term pulses had only a slight effect on uptake kinetics and, hence, on the threshold value, even if the population had been exposed several times to elevated concentrations above the steady-state level in the growth medium. The threshold value was also practically insensitive to the amount of phosphate stored during these short-term fluctuations. Long-term phosphate pulses resulted in a transition to a metastable state that was characterized by a severalfold higher threshold value. This transition, apparently an adaptation to the transiently elevated phosphate concentrations, was further studied by following the influx of 32 P-phosphate at constant external concentrations and was shown to be complete after a period of 10–20 min. After adaptation to pulses, the uptake behavior followed a linear flow-force relation over a wide range of external concentrations. This behavior was explained by the simultaneous operation of at least two uptake systems with different, but coordinated kinetic parameters. This linear flow-force relation facilitated a direct determination of the threshold value from uptake measurements. For applicability in the field the force-flow relation can be a diagnostic tool to assay for fluctuating phosphate and to establish threshold values below the normal measurable range . 相似文献
34.
Renate Kostrzewa und Achim Kostrzewa 《Journal of Ornithology》1997,138(1):73-82
Zusammenfassung In einer zeitgleichen Untersuchung über 10 Jahre (1985–94) wird die Brutbiologie des Turmfalken in 17 Gebieten Deutschlands verglichen. Insgesamt 3017 Brutpaare mit 11 423 Jungen sind untersucht worden (Tab. 1). Der Bruterfolg in den einzelnen Gebieten ist für jedes Gebiet spezifisch. Er schwankt in den unterschiedlichen Gebieten und Jahren um bis zu 4 Juv/+BP, in jedem Gebiet für sich betrachtet maximal bis 2,5 Juv/+BP. Bedeutung hat insbesondere der Einfluß des Brutplatztyps: Geschützte Brutplätze (in Gebäuden und Kästen) haben höheren Bruterfolg 4 Juv/+BP als offene Brutplätze (Baumnester, Körbe), in denen 4 Juv/+BP ausfliegen. Die Gründe hierfür werden diskutiert.
Breeding success of the KestrelFalco tinnunculus in Germany: results 1985–1994
We compare breeding biology and success of 17 Kestrel subpopulations in Germany in 1985–1994. A total sample of 3,017 breeding attemps and 11,423 fledged young were analyzed by our study group. Breeding success was not parallel over years and study areas; differences were up to four fledged young per successful pair, area and year. Within areas the differences reached 2,5 fledged young per successful pair. The most striking result was the influence of nesting site on breeding success. Clutches in sheltered sites in buildings or in nest boxes always reached mean values above 4 fledged young per successful pair, open nest sites like crow nests, however, were most clearly below this value.相似文献
35.
High Mobility Group 1 Protein Is Not Stably Associated with the Chromosomes of Somatic Cells 总被引:11,自引:1,他引:10
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Luca Falciola Fabio Spada Sabina Calogero Gernot Lngst Renate Voit Ingrid Grummt Marco E. Bianchi 《The Journal of cell biology》1997,137(1):19-26
High mobility group 1 (HMG1) protein is an abundant and conserved component of vertebrate nuclei and has been proposed to play a structural role in chromatin organization, possibly similar to that of histone H1. However, a high abundance of HMG1 had also been reported in the cytoplasm and on the surface of mammalian cells. We conclusively show that HMG1 is a nuclear protein, since several different anti-HMG1 antibodies stain the nucleoplasm of cultured cells, and epitope-tagged HMG1 is localized in the nucleus only. The protein is excluded from nucleoli and is not associated to specific nuclear structures but rather appears to be uniformly distributed. HMG1 can bind in vitro to reconstituted core nucleosomes but is not stably associated to chromatin in live cells. At metaphase, HMG1 is detached from condensed chromosomes, contrary to histone H1. During interphase, HMG1 readily diffuses out of nuclei after permeabilization of the nuclear membranes with detergents, whereas histone H1 remains associated to chromatin. These properties exclude a shared function for HMG1 and H1 in differentiated cells, in spite of their similar biochemical properties. HMG1 may be stably associated only to a very minor population of nucleosomes or may interact transiently with nucleosomes during dynamic processes of chromatin remodeling. 相似文献
36.
Androgen Ablation Leads to an Upregulation and Intranuclear Accumulation of Deoxyribonuclease I in Rat Prostate Epithelial Cells Paralleling Their Apoptotic Elimination 总被引:1,自引:0,他引:1
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37.
Attempts to induce enantioselectivity in the catalytic hydrogenation of unsymmetrically substituted aromatics using covalently bound, well known chiral auxiliaries are described. Marked differences in stereoselectivity and rate of hydrogenolysis are noted as a function of the auxiliary used. Enantioselectivities obtained in the resulting cyclohexyl derivatives are rather poor. © 1995 Wiley-Liss, Inc. 相似文献
38.
Werner Dietrich Mörschel Erhard Kort Renate Mellor Robert B. Bassarab Stephan 《Planta》1984,162(1):8-16
In nodules of Glycine max cv. Mandarin infected with a nod +fix- mutant of Rhizobium japonicum (RH 31-Marburg), lysis of bacteroids was observed 20 d after infection, but occurred in the region around the host cell nucleus, where lytic compartments were formed. Bacteroids, and peribacteroid membranes in other parts of the host cell remained stable until senescence (40d after infection). With two other nod+ fix- mutants of R. japonicum either stable bacteroids and peribacteroid membranes were observed throughout the cell (strain 61-A-165) or a rapid degeneration of bacteroids without an apparent lysis (strain USDA 24) occurred. The size distribution of RH 31-Marburg-infected nodules exhibited only two maxima compared with four in wild-type nodules and nodule leghaemoglobin content was found to be reduced to about one half that of the wild type. The RH 31-Marburg-nodule type is discussed in relation to the stability of the bacteroids and the peribacteroid membrane system in soybean. 相似文献
39.
40.
Zusammenfassung In der Frucht vonPoncirus trifoliata liegen in der Außenschale Drüsenzellkomplexe, die ein monoterpenreiches ätherisches Öl mit geringem Anteil an Sesquiterpenen und O-haltigen Substanzen produzieren. Ähnlich aussehende Exkretzellkomplexe aus den Saftschläuchen enthalten hauptsächlich Sesquiterpenkohlenwasserstoffe (STKW) und O-haltige Komponenten und sehr wenig Monoterpenkohlenwasserstoffe (MTKW). Im Schalenöl konnten nach gaschromatographischer Trennung mit Hilfe der Massenspektrometrie 19 Komponenten identifiziert werden, im Saftschlauchöl 25.Elektronenmikroskopische Aufnahmen der jüngsten Drüsenzellen beider Drüsenkomplexe lassen erkennen, daß beide Terpenklassen wahrscheinlich hauptsächlich bzw. ausschließlich plastidär entstehen.Exogen angebotenes14CO2 wird zunächst überwiegend in die MTKW eingebaut, erst später nimmt die Markierung der STKW und O-haltigen Komponenten stark zu. Über den Ferntransportweg angebotenes14C-Leucin führt anfangs zu einer starken Markierung der STKW und O-haltigen Komponenten, erst später verschiebt sich der Einbau etwas mehr in Richtung MTKW. Als Hauptursache für den differenten Einbau wird das Vorhandensein zweier Typen von Drüsenzellkomplexen mit unterschiedlichen Syntheseleistungen angesehen.Die aus dem14CO2 in der Außenrinde gebildeten Assimilate werden zuerst in das MTKW-reiche Öl der Schalenexkretbehälter eingebaut. Die überwiegend STKW erzeugenden Saftschlauchbehälter werden erst später beliefert. Beim Leucinangebot über die Fruchtstiele scheint es gerade umgekehrt zu verlaufen. Die aufeinanderfolgenden Maxima der Ölproduktion in den beiden Drüsenzellkomplex-Typen und die Änderung des Komponentenspektrums ihres ätherischen Öls im Verlauf der Vegetationsperiode tragen ebenfalls zu einem je nach Jahreszeit unterschiedlichen Einbau in die MTKW und STKW bei.
Compartmentation of mono- and sesqui-terpene biosynthesis of the essential oil inPoncirus trifoliata
Summary The fruit ofPoncirus trifoliata shows glandular cell complexes in the exocarp, which produce a volatile oil rich in monoterpenes but poor in sesquiterpenes and oxigenated compounds. The juice vesicles of the endocarp possess similar cell complexes mainly containing sesquiterpenes and oxigenated compounds, whereas monoterpenes only occur in small amounts. By the use of combined gas chromatography-mass spectrometry 19 components of the rind oil and 15 compounds of the endocarp oil could be identified.As demonstrated by electron microscopy the terpenes most probably are synthesized predominantly, if not exclusively in plastids. As shown by gasradiochromatography radioactive precursors (14CO2 and14C-leucine) are incorporated into mono- and sesqui-terpenes to a different extent.This is due to two gland types producing essential oils of different composition with regard to their mono- and sesqui-terpene percentage. In fruit development the exocarp glands differentiate earlier than the endocarp glands do. The activity of exogenously applied14CO2 first reaches the peripheral glands and later on appears in the interior glands. Depending upon the growth season, labelled leucine transported by the conducting tissues from lower plant parts leads to a high specific activity of the sesqui-terpenes and oxigenated compounds. It could be argued that in this instance the glands of the pulp are better provided with precursors than the exocarp glands. The successive maxima of essential oil production in both glandular complexes, and the changes in the concentration of individual oil constituents during the ontogeny of the fruit also contribute to different incorporation ratios of radioactive precursors into mono- and sesqui-terpenes.相似文献