Inversionen und chromosomale Strukturtypen bei Drosophila subobscura Coll

Zusammenfassung 1. Auf Grund der Untersuchung von zahlreichen Stämmen von Drosophila subobscura, die aus Köderfängen in der Natur an verschiedenen Orten in Österreich, Oberitalien, der Schweiz, England und einigen außereuropäischen Ländern abgeleitet worden waren, wurde ein Verzeichnis aller bisher bei dieser Art festgestellten natürlichen Inversionen gegeben, wobei die Anordnung des strukturell homozygoten Stammes Küsnacht als Standardanordnung diente.2. Durch den Vergleich von Stämmen, durch deren Kreuzung mit dem Standardstamm, durch die Ableitung von Inzuchtlinien aus verschiedenem Ausgangsmaterial und deren Kreuzung mit bestimmten Stämmen wurde die Zahl und der Bau der chromosomalen Strukturtypen ermittelt, auf deren Koexistenz in der Population die Mannigfaltigkeit der beobachteten Inversionsbilder beruht.3. Die Verteilung der Inversionen auf die verschiedenen Chromosomen des Satzes ist nicht zufällig. Auch die relative Länge der Inversionen scheint nicht rein zufallsmäßig zu sein.4. Bei den Bruchstellen der Inversionen finden sich auffallend oft Koinzidenzen, bis zu 5 Bruchstellen an einem Ort eines Chromosoms. Wie eine statistische Überlegung zeigt, können diese nicht zufallsmäßig bedingt sein. Es werden einige hypothetische Deutungsmöglichkeiten dieses Phänomens vorgelegt.5. Es wird die phylogenetische Ableitung der Strukturtypen der verschiedenen Chromosomen diskutiert.Mit 7 Textabbildungen.     

Effects of temperature and photoperiod on flowering in Hyptis brevipes

Few tropical species have been tested for their flowering response under controlled conditions. Hyptis brevipes Poit, is an annual herb, commonly found in wet margins of streams and ponds, being considered a weed for some perennial plantations in Brazil. Under experimental glasshouse conditions, this species proved to be an obligate short-day plant. Flowering was delayed when photoperiods longer than 8 h were given, the critical photoperiod being between 12 and 13 h. When both temperature and photoperiod were controlled, at 20°C a longer protoperiod (by almost 1 h) is still inductive compared to 25 and 30°C. The number of short-day cycles required for full induction is relatively high and dependent upon temperature; at 20°C or above, 10 cycles are adequate, but at 15°C, more short-day cycles are needed. The number of inflorescences formed as well as the floral index vary according to daylength × temperature × inductive cycle number, allowing flowering to be assessed quantitatively. Long days are inhibitory to flowering, either suppressing it completely (when symmetrically intercalated among 24 inductive cycles) or preventing the floral index from increasing.     

Molecular basis of intercellular adhesion in the biofilm-forming Staphylococcus epidermidis

The Staphylococcus epidermidis genes icaABC are involved in the synthesis of the polysaccharide intercellular adhesin (PIA), which is located mainly on the cell surface, as shown by immunofluorescence studies with PIA-specific antiserum. PIA was shown to be a linear β-1,6-linked glucosaminoglycan composed of at least 130 2-deoxy-2-amino-D-glucopyrano-syl residues of which 80–85% are N-acetylated, the rest being non-N-acetylated and positively charged. A transposon insertion in the icaABC gene cluster (ica, intercellular adhesion) led to the loss of several traits, such as the ability to form a biofilm on a polystyrene surface, cell aggregation, and PIA production. The mutant could be complemented by transformation with the IcaABC-carrying plasmid pCN27. Transfer of pCN27 into the heterologous host Staphylococcus carnosus led to the formation of large cell aggregates, the formation of a biofilm on a glass surface, and PIA expression. The nucleotide sequence of icaABC suggests that the three genes are organized in an operon and that they are co-transcribed from the mapped ica A promoter. Ica A contains four potential transmembrane helices, indicative of a membrane location. The deduced Ica A sequence shows similarity to those of polysaccharide-polymerizing enzymes, the most pronounced being with a Rhizobium meliloti N-acetylglucosaminyltransferase involved in lipo-chitin biosynthesis (22.5% overall identity and 37.4% overall similarity). This similarity suggests that Ica A has N-acetylglucosaminyltransferase activity in the formation     

Upper cretaceous rudist and stromatoporid associations of Central Oman (Arabian Peninsula)

Summary Rudist and stromatoporid associations of the Campanian from Central Oman are nearly monospecific. They are dominated byDurania aff.nicholasi, Vaccinites vesiculosus, Torreites milanovici or phaceloid and massive stromatoporids. Several other rudist genera play a secondary role. The thickness of the associations is rarely more than one metre. Solitary corals do not occur in the associations. Colonial corals are less common, although they are up to 1 m high and show considerable diversity. There are no binders. The reef structure indicates variable hydrodynamic conditions. They are always associated with very shallow water. The pureDurania aff.nicholasi patches with large colonial corals andTorreites milanovici are presumably the most rigid structures. The near monospecific associations ofVaccinites vesiculosus are widely distributed. Although mostly preserved in situ, strong currents, presumably caused by tropical storms, have repeatedly impaired and interrupted growth. The specific growth characteristics of the shell of some rudists, especially the radiolitids, enable an estimation of the individual lifespan. Frameworks of approximately 1 metre thickness probably developed in ±100 years. The sediments of the complete sections are predominantly bioclastic.     

Cloning and electrophysiological analysis of KST1, an inward rectifying K+ channel expressed in potato guard cells.

Potassium uptake by guard cells represents part of the osmotic motor which drives stomatal opening. Patch-clamp measurements have identified inward rectifying K+ channels capable of mediating K+ uptake in guard cells and various other plant cell types. Here we report the molecular cloning and characterization of a voltage-dependent K+ channel (KST1) from potato (Solanum tuberosum L.) guard cells. In situ hybridization shows expression of kst1 in guard cells. Two-electrode voltage-clamp and patch-clamp studies of the gene product after cRNA injection into Xenopus oocytes identified KST1 as a slowly activating, voltage-dependent, inward rectifying K+ channel. The single channel current voltage curve was linear in the range -160 to +20 mV, with a deduced single channel conductance of 7 pS in symmetrical 100 mM K+. This channel type, modulated by pH changes within the physiological range, required ATP for activation. In line with the properties of a K(+)-selective channel, KST1 was permeable to K+, Rb+ and NH4+ and excluded Na+ and Li+. Cs+ at submillimolar concentrations blocked the channel in a voltage-dependent manner. Related studies on potato guard cell protoplasts confirmed the biophysical characteristics of the kst1 gene product (KST1) in the heterologous expression system. Therefore, KST1 represents a major K+ uptake channel in potato guard cells.     

Auswirkungen von Hochspannungstrassen auf die Fl?chennutzung überwinternder Bl??- und Saatg?nseAnser albifrons, A. fabalis

Zusammenfassung  Während das Mortalitätsrisiko für Vögel durch Drahtanflug und Stromschlag an Hochspannungsleitungen vielfach untersucht wurde, könnte auch ein Einfluß von Hochspannungstrassen (110 kV) auf Vögel bestehen, die sich am Boden aufhalten. Dieser wurde 1994/95 am Beispiel der Flächennutzung überwinternder Bläß- und Saatgänse (Anser albifrons, A. fabalis) am Unteren Niederrhein untersucht. Da Gänse offene ungestörte Äsungsflächen beanspruchen, wurde der Arbeitshypothese nachgegangen, daß trassennahe Bereiche von Gänsen gemieden bzw. vermindert genutzt werden. Die Besuchsfrequenz von vier häufig genutzten trassenüberspannten Äsungsflächen wurde ermittelt. Im Anschluß an die einzelnen mehrtägigen Beäsungsphasen wurde die Losungsdichte (LD) als Maß der Flächennutzung senkrecht zum Trassenverlauf bestimmt. An 16–20 m hohen Trassen stieg die LD mit zunehmender Entfernung zur Trasse. Eine signifikante Abnahme der LD trat unterhalb von 40–80 m Abstand zur Trasse ein. Kleine Teilflächen, die durch die Trassen von größeren Bereichen abgetrennt sind, wurden weniger genutzt. An einer 60 m hohen, den Rhein Überquerenden Trasse, konnte kein trassenbedingter Unterschied der LD festgestellt werden. Mögliche Ursachen für die beschriebenen Effekte werden diskutiert.

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The impact of power lines on field selection and grazing intensity of wintering White-fronted- and Bean GeeseAnser albifrons, A. fabalis

In addition to studies about the mortality risk by collision and electrocution power lines may have an impact on birds during foraging behaviour on the ground. We examined this question in geese (Anser albfrons, A. fabalis) wintering in the lower Rhine area of North Rhine Westfalia (FRG) 1994/95. Because geese prefer large areas with low levels of disturbance by human activities or urbanic structures like buildings or roads, we hypothesized that they might be disturbed by the presence of power lines in their foraging sites and thus avoid areas next to the lines. To quantify the grazing intensity in relation to the distance from the power lines (110 kV), dropping densities have been repeatedly counted after independant grazing intervals in four different feeding sites. Our data show that: 1. Grazing intensity increases with the distance to power lines of low height. Significantly reduced grazing levels have been found in distances less than 80 to 40 m to the power lines. 2. No effects have been observed for a power line in an area next to the river rhine where the wires crossed the ground in a height of about 60 metres. 3. In small pasture or field areas, cut off by power lines from large ones, a generally reduced grazing amount is evident. Several conceivable reasons for the described effects are discussed.