Die Korrelation von Körperlänge,Augen-, Linsen- und Pupillengrösse bei Hybriden ausAstyanax × Anoptichthys (Characidae,Pisces)

Ohne Zusammenfassung     

Dose-response function for Painter's SCE-model

Summary The replication model for sister chromatid exchange (SCE), when introduced in 1980 by Painter, was claimed to be consistent with the one hit property of SCE. However, the argument offered in favour of the one hit property was based on a defective dose-response function, as shown in this paper, since dose as the independent parameter of any dose-response function was not included in the considerations. This missing part of the model's dose-response function is added and, by using Bessel functions, a formula for the complete dose-response function is presented. A re-examination of the newly derived function shows that, in the model, linearity holds only under certain restricted circumstances.     

Regulation of amino acid transport in growing cells of Streptomyces hydrogenans

(1) The active uptake of different amino acids by growing cells of Streptomyces hydrogenans was shown to be correlated with the physiological age of the cells. During the lag phase of growth the transport capacity increased and attained its highest level when the growth rate was maximum. During further growth the transport capacity declined progressively. The lowest transport activity was observed when the culture shifted into the stationary growth phase. (2) Such modulation of transport capacity was independent on the presence or absence of amino acids in the growth medium of the cells. (3) The size and the composition of the pool of free intracellular amino acids was also undergoing substantial variations during the growth cycle of the culture. In the lag phase, the levels of all amino acids decreased markedly and attained their lowest values at the end of this phase. During further growth the pool size was slowly replenished. (4) Removal of the pool resulted in a considerable gain of transport capacity. Therefore, it was concluded that active amino acid transport in growing Streptomyces hydrogenans is under feedback control by intracellular amino acids. (5) Quantitatively, the modulation of the pool size could not fully account for the variation of the transport capacity. Since a pool-independent stimulation of transport was found to be correlated with the increase of the growth rate of the cells, the possibility is discussed that the stimulation of transport is either due to increased levels of distinct RNA species, which might provide positive feedback signals for transport, or by increased rates of de novo synthesis of transport limiting proteins.List of Abbreviations AIB 2-aminoisobutyric acid - CM complete medium - MM mineral medium     

Silicium-Stoffwechsel bei Mikroorganismen

Zusammenfassung Untersuchungen zur Mobilität der aufgenommenen Kieselsäure in Bakterien zeigen, daß die Kieselsäure in Abwesenheit von Glucose rasch wieder gegen Phosphat ausgetauscht werden kann. Wenn jedoch die Aufnahme der Kieselsäure aus glucosehaltigen Si-Lösungen erfolgte, so ergibt sich, daß nur ein geringer Teil dieser Kieselsäure durch Inkubation in Phosphatlösungen wieder ausgetauscht werden kann. Dieser Si-Anteil wird jedoch bei Inkubation der Zellen in Carbonatlösung vollständig ausgeschieden. Die Möglichkeit, daß diese Kieselsäure in Form von C–Si-Bindungen in der Zelle vorliegt, wird diskutiert. Weitere Untersuchungen zu diesen Fragen sind im Gange.

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Summary Studies on the mobility of silicon in bacterial cells show, that Si is readily excanged against phosphate if the cells are incubated in absence of glucose. However if the bacteria are preincubated in silicate solutions in the presence of glucose, the silicon taken up is not mobile any more during incubation in phosphate solutions. The element is extruded completely by incubating the cells in carbonate solutions. Evidence has been made that silicon is deposited within the cells as organic compound in which C–Si-bonds are formed.

     

Spherical subunits in photosynthetic membranes of two cyanophyceae and the bacterium rhodospirillum rubrum

Summary The photosynthetic lamellae of Oscillatoria amoena and Pseudanabaena catenata appear as a two-dimensional packing of spherical units following permanganate fixation, ultrathin sectioning and high-resolution electron micrography. The usual three-layered appearance is explained as an optical artifact. Quite similar patterns were observed in chromatophore membranes of Rhodospirillum rubrum. Also, the cytoplasmic membrane of R. rubrum shows an identical pattern.Indication is presented that thylakoids of Cyanophyceae can arise as invaginations of the cytoplasmic membrane.The localization of chloroplast lipids in these organisms and the similarity of spherical units and quantasomes is discussed.     

Die Chloroplastendrehung beiMougeotia

Summary Mougeotia cells with chloroplasts oriented in profile have been irradiated with small spots of monochromatic red polarized light in order to induce chloroplast movement.In these experiments, four factors have been varied: 1. the orientation of the vibration plane of the light in relation to the cell axis, 2. the localization of the spot, i. e. irradiation of the chloroplast or the cytoplasm, 3. the spot size, and 4. the duration of the irradiation.As a result of our experiments, we conclude that the photoreceptor molecules responsible for the light-induced chloroplast movement are localized in the cytoplasm.As the photoreceptor of this reaction is the well known phytochromesystem, we may assume that also in other plants the phytochrome is localized in the cytoplasm rather than in the chloroplast.

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