Wachstum und Zellteilung beiUrospora

Zusammenfassung 1. Alle Zellen einesUrospora-Fadens sind teilungs- und streckungsfähig.2. Mit zunehmendem Alter der Pflanze verschiebt sich die Zone des stärksten Wachstums von der Spitze zur Basis.3. Längs eines Fadens bilden sich von Tag zu Tag wechselnde Teilungszonen aus.4. Im allgemeinen erreicht eine junge Zelle nach vier Tagen wieder die teilungsfähige Länge.5. Bei täglich 14stündiger Lichteinwirkung beginnen die Zellteilungen etwa eine Stunde vor dem Dunkelwerden und erstrecken sich — nicht gleichzeitig in allen Zellen — über fünf Stunden.6. Vor der Zellteilung ordnet sich ein Teil der Kerne in einer äquatorialen Gürtellinie an.7. Sämtliche Kerne einer Zelle teilen sich gleichzeitig. Ihre Anzahl wird durch die Zellteilung nicht verändert.8. Die Vermehrung der Kerne erfolgt durch freie, das heißt von der Zellteilung unabhängige Mitosen in Zellen, die noch nicht die teilungsfähige Länge erreicht haben.

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Growth and cell-division inUrospora

Cultures ofUrospora wormskioldii were used for studying growth and details of cell-division in this alga. In general, all cells of a filament are able to divide in a four-day-rhythm. During this period, the length of the filament nearly doubles. The zone of most active cell-division changes with the age of the plant, moving downward from the top to the base of the filament. The uppermost cells may become fertile while the basic ones continue to divide. Cell-division does not occur simultaneously in all cells of a filament. In a 14:10 hour rhythm of light and dark, divisions begin about one hour before the onset of the dark period and continue over the following five hours. In the growing cell, nuclei are distributed irregularly; before dividing, some of them arrange themselves in an equatorial line. All nuclei of a cell divide synchronously, the new wall differentiating from the uniting phragmoplasts of the neighbouring spindles. The number of nuclei does not vary because of cell-division; multiplication of nuclei in growing cells is brought about by mitosis without cell-division.

     

Indirekte Regelmechanismen der Stoffwechselgröße von Fischen

Metabolic rate does not strictly follow changes of influencing parameters. O₂-consumption by fish is ordinarily said to be independent from O₂-pressure throughout a wide range. This constancy is probably the result of a regulation. The metabolic rate itself or an auxiliary mechanism “before” or “after” metabolism may be regulated. On the basis of vanDam's paper (1938) and our own experiments, the problem whether or not O₂-pressure in blood serves as a regulated auxiliary mechanism in order to maintain a certain metabolic constancy is discussed. The disadvantage of such a regulation would be the energy demand of increased ventilation and circulation as compensating mechanisms. In accordance with this assumption we have found a rise in O₂-consumption at a somewhat reduced O₂-pressure. Locomotory behaviour supports the constancy of metabolic rate; thus a contrary shift of the temperature preferendum after application of substances which influence metabolism has been found.     

Zum Ortungsverfahren von Gyrinus substriatus Steph

Zusammenfassung Die vorliegende Arbeit befaßt sich mit dem Orientierungsvermögen des Taumelkäfers (Gyrinus substriatus) im Bereich der Wasseroberfläche mit Hilfe der Antennenorgane.Der Taumelkäfer besitzt eine hohe Empfindlichkeit gegenüber Oberflächenwellen und ist in der Lage, deren Einfallsrichtung festzustellen. Im Nahbereich werden Hindernisse, die in die Wasserfläche eintauchen und einen Meniskus hochziehen, gut erkannt.Die mechanischen und elektrophysiologisohen Eigenschaften der Antennen werden ermittelt. Mechanische Erschütterungen rufen Relativbewegungen zwischen Pedicellus und dem frei in die Luft ragenden Flagellum hervor und erregen das Johnstonsehe Organ. Pedicellus und Flagellum sind als schwingungsfähiges System anzusehen, dessen Eigenfrequenz 250 Hz beträgt und dessen relatives Dämpfungsmaß etwa den Wert 0,7 hat. In dem in Frage kommenden Frequenzbereich bis 150 Hz arbeitet das Schwingungssystem vorwiegend als Beschleunigungsmesser.Die elektrophysiologischen Untersuehungsergebnisse stimmen gut mit den auf Grund der Schwingungsmessungen gefundenen Eigenschaften überein. In der vom Antennennerven abgenommenen elektrophysiologischen Signalspannung werden reizsynchrone Pulssalven beobachtet, denen sich bei steigender Erregungsfrequenz ein synchrones Summenpotential überlagert. Vergleiche mit den mechanischen Untersuchungsergebnissen zeigen, daß das Summenpotential seinen Ursprung im Johnstonschen Organ hat. Die Amplitude dieses Signals steigt proportional mit der Relativbewegung zwischen Flagellum und Pedicellus an; sie ist in einem weiten Bereich unabhängig von der Frequenz.Der Käfer ist in der Lage, äußerst feine Erschütterungen der Wasserfläche wahrzunehmen. Wasserwellen, deren Amplitude nur wenige m beträgt, bringen das Johnstonsche Organ zum Ansprechen. Die Empfindlichkeit nimmt mit steigender Frequenz zu. Hat der Käfer eine Eigengeschwindigkeit, die der Ausbreitungsrichtung eines Wellenzuges entgegengerichtet ist, so erkennt er diese Wellen auf Grund des Doppier-Effektes besser. Mit einer ähnlich guten Empfindlichkeit nimmt der Käfer in der Nähe von Hindernissen den Meniskus wahr. Die ansteigende Wasserfläche ruft infolge der Eigengeschwindigkeit des Käfers eine zeitlich sich ändernde Antennenauslenkung hervor. Bei normalen Schwimmgeschwindigkeiten ist sie bereits in der Entfernung von 0,5–1,5 cm vom Rand so groß, daß der Käfer reagiert.

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On the orientation of Gyrinus substriatus StephWhirligig beetle

Summary The orientation of whirligig beetles Gyrinus substriatus on the surface of water by means of the antennae has been investigated. Whirligig beetles are very sensitive to waves on the surface and are able to find out the direction from where the waves come. They are also able to perceive objects which dip into the water surface and form a meniscus.The antennae have been investigated mechanically and electrophysiologically. Mechanic percussions produce movements between the pedicellus and the flagellum which does not touch the surface of water (Figs. 2, 14). These movements excite the Johnston-Organ. Pedicellus and Flagellum form a vibration system; the resonance-frequency is about 250 Hz and the relative attenuation constant is about 0,7. In the interesting frequency range below 150 Hz the system is mainly measuring accelerations.The results of electrophysiological investigations show a good conformity with those found by mechanical measurements. In the electrophysiological signal, derived from the antenna nerve, groups of spikes are to be observed which are in synchronism with the exciting signal. By increasing the exciting frequency a synchronous sum potential appears which is superimposed upon the original signal (Figs. 19...21).Comparisons with mechanical investigations show that the sum potential has its origin in the Johnston-Organ. The amplitude of this signal increases proportionally to the relative motion between flagellum and pedicellus, independent of frequency in a wide range (Fig. 23).The beetle is able to perceive very small percussions of the surface of water. Waves on the surface with an amplitude of several m produce a response in the Johnston-Organ. The sensivity increases with increasing frequency (Fig. 31). If the beetle is moving against a train of waves, it will perceive them better by reason of the Doppler-Effect.The sensivity is similar when the beetle approaches the meniscus near objects. The inclined water surface produces an excursion of the antenna as a function of time depending on the velocity of the beetle. At normal velocities and in an distance of 0.5–1.5 cm this effect will be large enough to produce a response (Fig. 32).

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Der Verfasser dankt Herrn Prof. Dr.-Ing. habil. H. Tischner und Herrn Dr.-Ing. A. Schief für die Anregung zu diesen Untersuchungen und dem Herrn Ministerpräsidenten des Landes Nordrhein-Westfalen — Landesamt für Forschung — für die Bereitstellung der Mittel.     

The efficacy of biobehavioral and compliance interventions in the adjunctive treatment of mild pregnancy-induced hypertension

This investigation assessed the efficacy of a biobehavioral intervention in the adjunctive treatment of mild pregnancy-induced hypertension (PIH), a potentially serious complication of pregnancy in which normotensive women develop hypertension, proteinuria, and edema of unknown etiology late in gestation. Forty-five women with symptoms of PIH were randomly assigned to one of three treatment conditions: bed rest alone (the most common obstetrical treatment), bed rest with individualized compliance enhancement training, or a four-session biobehavioral treatment consisting of bed rest, compliance enhancement training, and individualized thermal biofeedback-assisted relaxation training. Results indicated that while blood pressure for the bed rest and compliance enhancement groups continued to rise and pose an increasing health risk to maternal and fetal well-being, subjects in the biobehavioral group maintained their blood pressure at a significantly lower, and presumably safer, level. The biobehavioral treatment is hypothesized to affect blood pressure levels in subjects with mild PIH through the mediation of the sympathetic nervous system, decreasing peripheral vascular resistance and cardiac output. The results of this investigation suggest that the biobehavioral intervention may be an effective adjunct to bed rest in the treatment of mild PIH remote from term.     

Essential function in chloroplast recognition of the ferredoxin transit peptide processing region

Molecular Genetics and Genomics - Plant ferredoxin is a nuclear-encoded chloroplast protein that is synthesized in the cytoplasm as a transit peptide-containing precursor molecule. To identify...     

The atokous-epitokous border is determined before the onset of heteronereid development in Platynereis dumerilii (Annelida,Polychaeta)

Summary In most nereids sexual maturation is accompanied by a dramatic reorganization of the body that enables swarming of the formerly benthic worms. However, a border exists between unchanged anterior (atokous) and metamorphosed posterior (epitokous) segments. The site of this atokous-epitokous border (a/e border) is different in sexually mature males and females of Platynereis dumerilii. There is no correlation between the total number of setigerous segments of a specimen and the location of the a/e border. The location of the a/e border and sexual development are affected neither by cutting off caudal segments of juveniles (including the prospective a/e border) nor by transecting the ventral nerve cord. When parapodia are transplanted from prospective epitokous regions to prospective atokous regions and vice versa, they maintain their original character during metamorphosis. The results presented here suggest that prospective atokous as well as epitokous characters are determined at or only very shortly after formation of the respective segments. Thus the a/e border is established well in advance of the onset of epitokous metamorphosis.