Spatial memory and orientation strategies in the elasmobranch<Emphasis Type="Italic"> Potamotrygon motoro</Emphasis>

We investigated whether juvenile freshwater stingrays (Potamotrygon motoro) can solve spatial tasks by constructing a cognitive map of their environment. Two experimental conditions were run: allocentric and ego-allocentric. Rays were trained to locate food within a four-arm maze placed in a room with visual spatial cues. The feeding location (goal) within the maze (room) remained constant while the starting position varied for the allocentrically but not for the ego-allocentrically trained group. After training, all rays solved the experimental tasks; however, different orientation strategies were used within and between groups. Allocentrically trained rays reached the goal via novel routes starting from unfamiliar locations, while ego-allocentrically trained rays primarily solved the task on the basis of an egocentric turn response. Our data suggest that P. motoro orients by constructing a visual cognitive map of its environment, but also uses egocentric and/or other orientation strategies alone or in combination for spatial orientation, a choice which may be governed by the complexity of the problem. We conclude that spatial memory functions are a general feature of the vertebrate brain.     

The solution structure of a transient photoreceptor intermediate: Delta25 photoactive yellow protein

The N-terminally truncated variant of photoactive yellow protein (Delta25-PYP) undergoes a very similar photocycle as the corresponding wild-type protein (WT-PYP), although the lifetime of its light-illuminated (pB) state is much longer. This has allowed determination of the structure of both its dark- (pG) as well as its pB-state in solution by nuclear magnetic resonance (NMR) spectroscopy. The pG structure shows a well-defined fold, similar to WT-PYP and the X-ray structure of the pG state of Delta25-PYP. In the long-lived photocycle intermediate pB, the central beta sheet is still intact, as well as a small part of one alpha helix. The remainder of pB is unfolded and highly flexible, as evidenced by results from proton-deuterium exchange and NMR relaxation studies. Thus, the partially unfolded nature of the presumed signaling state of PYP in solution, as suggested previously, has now been structurally demonstrated.     

Abhängigkeit der Kompetenz des Amphibien-Ektoderms von der Proteinsynthese

Zusammenfassung Isoliertes Gastrula-Ektoderm des Amphibienkeimes wurde nach unterschiedlicher vorhergehender Behandlung mit einer mesodermal/neural induzierenden Rohfraktion (Versuchsreihe I) und einer mesodermal/entodermal induzierenden Fraktion (Versuchsreihe II) behandelt (Sandwich-Methode).In der Kontrollserie (K₀) wurde frühes Gastrula-Ektoderm sofort mit dem Induktor versehen.Die Explantate der Serie K₁ wurden 20 Std (Versuchsreihe I) bzw. 24 Std (Versuchsreihe II) in vitro kultiviert und dann erst mit dem Induktor versehen.In einer dritten Serie wurden die Explantate über 20 bzw. 24 Std mit einem Hemmer der Proteinsynthese (2g/ml Aktidion = Cycloheximid) behandelt und anschließend mit Induktor in normaler Holtfreter-Lösung aufgezogen.Während gealtertes Ektoderm (Serie K₁) seine Reaktionsfähigkeit (Kompetenz) nach 24stündiger in vitro-Kultivierung verliert, weisen die ebensolange mit Aktidion behandelten Explantate keinen Kompetenzverlust auf.

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Relationship between competence and protein synthesis in amphibian ectoderm

Summary Isolated Amphibian gastrula ectoderm was pretreated in different ways and induced with a mesodermal/neural (Series I) or a mesodermal/endodermal (Series II) fraction (sandwich method).In the controls (K₀) the inducer was implanted directly into early gastrula ectoderm. The explants of series K₁ were cultured in vitro for 20 (Series I) or 24 hours, respectively (Series II), and then combinated with the inducer. In series Ak the explants were treated with an inhibitor of protein synthesis (2g/ml Actidion = Cycloheximid) for 20 or 24 hours and then cultured with inducer for 12 days.Ectoderm, cultured for 24 hours in vitro (Series K₁) lost its ability to respond to inducing factor. There is no loss of competence when ectoderm is treated with actidion for the same time and then treated with inducer.

     

UV-Spektren und Elektronenstrukturen von Monoamino-Acridinium-Kationen

Zusammenfassung Es wurden die UV-Spektren und die Fluoreszenzanisotropie der 1-, 2-, 3- und 4-Amino-Acridinium-Kationen gemessen und mit Hilfe nach PPP berechneter Anregungsenergien, Übergangsmomente und Polarisationen gedeutet. Die Rechnungen liefern die Elektronenstrukturen der Grund- und Anregungszustände (-Bindungsordnungen und -Elektronendichten). Die Elektronenanregungen der Kationen sind über diejenigen der nicht ionisierten Basen mit denen des Kohlenwasserstoffs Anthracen als Grundkörper zu korrelieren. Der Einfluß von Wasserstoffbrückenbindungen auf die Spektren wird diskutiert. Wir danken der D. F. G. und den Rechenzentren in Darmstadt und Freiburg.

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UV-spectra and -electronic structures of monoamino-acridinium cations

Summary The electronic-excitation and polarisation-spectra of 1-, 2-, 3- and 4-amino-acridinium cations were measured. Transition energies, -electronic densities and -bond orders have been calculated by a -variable SCF-method within the general PPP-framework; the effect of H-bond formation upon their electronic spectra is examined and attempts are being made to correlate the computed transitions of the monoamino-acridinium cations with those of the corresponding non-ionized bases and with anthracene.

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Wir danken der D. F. G. und den Rechenzentren in Darmstadt und Freiburg.     

Beobachtungen am Horst des Schwarzen Storches (Ciconia nigra L.)

Ohne ZusammenfassungMit freundlicher Genehmigung des Verlages entnommen dem soeben erschienenen Buche: Störche. Erlebnisse mit dem Schwarzen und Weißen Storch. VonHorst Siewert, Berlin 1932. Verlag vonDietrich Reimer. 8°. 208 Seiten, mit 80 Bildertafeln nach Aufnahmen des Verfassers. Leinenband Preis M. 4.80.     

Eolimna martinii n. gen., n. sp. (Bacillariophyceae) aus dem Unter-Oligozän von Sieblos/Rhön im Vergleich mit ähnlichen rezenten Taxa

The laminated sediments of the Lower Oligocene ‘Sieblos-Schichten’ (dysodile and kieselgur-sediments) contain many individuals of a naviculoid diatom species. Formerly this group of diatoms would have been classified without doubt as Navicula (section ‘Minusculae’). After splitting this extremely heterogeneous genus in Navicula sensu stricto and some other homogeneous genera, the pattern of structures of this fossil species does not correspond to any established genus. For that reason this form will be described as the generotype of a new genus Eolimna. Furthermore it became evident that some Recent species (assigned to Navicula) show the same pattern of structures as the new genus Eolimna (generotype: E. martinii) which represents one of the first naviculoid diatoms of limnic origin. The essential criteria of this genus are: comparatively small cells with narrow girdle; simple alveolated rib system; areolae with a hymen in approximately medium position between relatively large sized foramina outside and inside of the valve; a single row of more or less irregular arranged areolae in close position to each other, on one or several of the copulae. The differences to supposed related genera are discussed.     

Induction of callose formation is a sensitive marker for genotypic aluminium sensitivity in maize

The screening of 37 Zea mays L. cultivars in nutrient solution using root elongation (24 h) as a parameter showed large genotypic differences in Al resistance among the genetic material evaluated.Callose concentrations in root tips were closely and positively related to Al-induced inhibition of root elongation. Therefore, Al-induced callose formation in root tips appears to be an excellent indicator of Al injury and can be used as a selection criteria for Al sensitivity. In contrast, aluminium concentrations in root tips were not related to Al-induced inhibition of root elongation, nor to Al-induced callose formation. Callose formation was also induced by short-term A1 treatment in root tip protoplasts, and the response of protoplasts clearly reflected the cultivar-specific response to Al of intact roots. This indicates that in maize, Al sensitivity is expressed on the protoplast level.     

The helper T-cell repertoire of mice expressing class II major histocompatibility complex β chains in the absence of α chains

 Mutant mice generated by disrupting the H2-Aa ^b major histocompatibility complex (Mhc) gene are demonstrated here to express Aβ^b chains in the absence of α chains. These mice possess a CD4⁺ helper T cell (Th) repertoire that uses predominantly the Vβ7 T-cell antigen receptor (Tcr) segment for recognition of any protein antigen presented by the α-free Aβ molecule. As an alloantigen, the Aα-free Aβ molecule is recognized very poorly by T cells from a series of class II disparate mouse strains, indicating that it is grossly different from normal α/β heterodimers. Indeed, molecular modeling suggests a β/β homodimer arrangement with an altered geometry of the Tcr contact area. Interestingly, the mutant mice exhibit normal alloreactivity, without a restricted Vβ usage, toward a series of foreign α/β class II heterodimers, although their T cells developed in the absence of such heterodimers. Thus, the complementarity of Tcr to normal α/β heterodimers, and thereby also alloreactivity, appears to be an ontogeny independent (i. e., germline-encoded) feature. Received: 30 September 1996 / Revised: 18 October 1996