Subunit structure of chromosomes in mitotic nuclei of Physarum polycephalum

We have investigated the subunit structure of mitotic chromosomes of the acellular slime mould Physarum polycephalum, using the nuclease susceptibility of isolated mitotic nuclei as a probe. A characteristic pattern of DNA digestion products is obtained, containing approximately integral multiples of a basic 140 base pair DNA segment that resembles very closely the pattern in G₂ phase nuclei of Physarum and of calf lymphocyte nuclei. These results demonstrate that during the process of chromosome condensation there is no alteration at the primary level of chromatin structure that is responsible for the characteristic DNA digestion pattern.     

Zur Biologie und Ökologie des Landeinsiedlerkrebses Coenobita scaevola Forskål am Roten Meer

Zusammenfassung Coenobita scaevola lebt an der Küste des Roten Meeres in sehr großer Individuenzahl. Sie ist an die Küstenlinie gebunden, da sie regelmäßig Wasser in ihre Kiemenhöhle und ihr Schneckenhaus aufnehmen muß, da sie nur hier Nahrung findet (Strandanwurf) und da sie nur hier Schneckenhäuser zum Schutz des weichen Hinterleibes gegen Strahlung, Austrocknung und mechanische Beschädigung findet. Die Tiere sind in Gebieten mit sehr wenig Strandanwurf nicht standorttreu, in Gebieten mit guten Lebensbedingungen dagegen bleiben sie lange Zeit. In verschiedenen, oft sehr nahe beieinander liegenden Gebieten sind die Einsiedler zu verschiedenen Tageszeiten rege, ohne daß eine Beziehung zu Temperatur, Luftfeuchte, Gezeiten und Feinden erkennbar wäre. Es wird erstmalig ein aktives Vermeiden von Bodenfallen durch Coenobita beschrieben. Coenobita scaevola lebt bei günstiger Temperatur (16–20°C) und günstiger Salinität (35–40) lange Zeit (über 20 Tage) unter Wasser.Die Osmoregulation der Landeinsiedler erfolgt in prinzipiell anderer Weise als bei den bisher bekannten Typen, sie ist mit den Ausdrücken Poikilosmotie oder Homoiosmotie nicht zu umschreiben. Vielmehr pendelt sich der Innendruck bei hohen Außendrucken auf höhere Werte ein als bei niedrigen Außendrucken; mittlere Blutwerte bleiben nur bei gleichzeitiger Gabe von Süß- und Seewasser erhalten.Die statischen Probleme, die sich für ein phylogenetisch junges Lufttier am Lande ergeben, meistert Coenobita durch eine regelmäßige Folge der Beinbewegung und durch anatomische Umkonstruktionen in den Beinen.Als phylogenetisch junges Landtier ist Coenobita von einer Fauna mariner und terrestrischer Herkunft besiedelt.

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Biology and ecology of the terrestrial hermit crab coenobita scaevola forskål of the Red Sea

Summary The terrestrial hermit crab Coenobita scaevola is very common on the coast of the Red Sea. The species depends on the sea for its source of food (wrack-fauna), source of drinking-water and water for moistening gills and abdomen. Only in the supra-litoral zone they find gastropod shells to protect their abdomen against insolation, desiccation and mechanical damage. Coenobita scaevola stays in one place for a long time if good living conditions are available. The time of activity of the juveniles differs from one place to another. Some are diurnal, others are nocturnal. There is no evident relation to the ecological factors. Most of the adults are nocturnal. No Coenobita could be collected in Barber traps. The avoidance of such traps by arthropodes has never been observed before. Coenobita scaevola can live for quite a long time under water of sufficient temperature and salinity. The osmotic regulation of the land-hermit crab differs from that of other shore animals. Coenobita can tolerate a wide range of blood concentrations (25–70). It controls the concentration of its blood by selecting water of the appropriate salinity.The static problems of Coenobita are solved by regular movement of the legs and special articulation of the legs.As Coenobita scaevola is a phylogenetically young land animal it carries many inhabitants of marine and terrestrial origin.

     

Dense-core vesicles and non-synaptic exocytosis in the central body of the crayfish brain

Summary The central body in the median protocerebrum of the brain of the crayfish Cherax destructor is a distinctive area of dense neuropile, the nerve fibres of which contain three main types of vesicles: electronlucent vesicles (diameter 35 nm), dense-core vesicles (diameter 64 nm), and large structured dense-core vesicles (diameter 98 nm, maximum 170 nm). Different vesicle types were found together in the same neurons. Electronlucent vesicles were seen at presynaptic sites and rarely observed in the state of exocytosis. Exocytosis of densecore and structured dense-core vesicles was a regular feature on non-synaptic release sites either close to, or at some distance from pre- and subsynaptic sites. Non-synaptic exocytotic sites are more often observed than chemical synapses. Different forms of exocytosis seen at non-synaptic sites included the release of single densecore vesicles, packets of dense-core vesicles, and rows of dense-core vesicles lined up along cell membranes and around fibre invaginations. Swelling and the enhanced electron density of extracellular non-synaptic spaces may mark the positions of prior exocytotic events. In vitro treatment of the brain with tannic acid buffer solution followed by conventional double fixation resulted in the augmentation of non-synaptic exocytosis. Electron microscopy of proctolin- and serotonin-immunoreactive nerve fibres shows them to contain dense-core and electron-lucent vesicles and to be surrounded by many unlabelled profiles similarly laden with dense-core vesicles and electron-lucent vesicles, indicating the presence of other, not yet identified, neuroactive compounds.     

Mitochondrial mutations restricting spontaneous translational frameshift suppression in the yeast Saccharomyces cerevisiae.

Summary The +1 frameshift mutation, M5631, which is located in the gene (oxi1) for cytochrome c oxidase II (COXII) of the yeast mitochondrial genome, is suppressed spontaneously to a remarkably high extent (20%–30%). The full-length wild-type COXII produced as a result of suppression allows the mutant strain to grow with a leaky phenotype on non-fermentable medium. In order to elucidate the factors and interactions involved in this translational suppression, the strain with the frameshift mutation was mutated by MnCl₂ treatment and a large number of mutants showing restriction of the suppression were isolated. Of 20 mutants exhibiting a strong, restricted, respiration-deficient (RD) phenotype, 6 were identified as having mutations in the mitochondrial genome. Furthermore, genetic analyses mapped one mutation to the vicinity of the gene for tRNA^Pro and two others to a region of the tRNA cluster where two-thirds of all mitochondrial tRNA genes are encoded. The degree of restriction of the spontaneous frameshift suppression was characterized at the translational level by in vivo ³⁵S-labeling of the mitochondrial translational products and immunoblotting. These results showed that in some of these mutant strains the frameshift suppression product is synthesized to the same extent as in the leaky parent strain. It is suggested that more than one +1 frame-shifted product is made as a result of suppression in these strains: one is as functional as the wild-type COXII, the other(s) is (are) non-functional and prevent leaky growth on non-fermentable medium. A possible mechanism for this heterogenous frameshift suppression is discussed.     

Non-destructive assay systems for detection of β-glucuronidase activity in higher plants

β-glucuronidase (GUS) can be qualitatively assayed in seedlings and fully grown plants without injury or irreversible damage by short term incubations in X-gluc or by spraying 4-MUG.     

An unusual cell in the central nervous system of Hirudo medicinalis L.: a neuron with ribbons and flags

Summary A neuron (cell 151) with the ability to silence efferent activity in the roots of a leech segmental ganglion was filled with horseradish peroxidase and studied by light-and electron microscopy. The neurites of cell 151 penetrate all areas of the neuropile except for a thin ventral layer. The branching pattern of the secondary neurites is highly variable. Post-and presynaptic structures of chemical synapses with clear vesicles of 25 nm diameter were identified. Neurites are mostly wrapped in glia and run in bundles among other axons. They frequently form ribbons which are 20–40 nm thick, extend several microns away from the dendrite and are followed up to 3 m in depth. They also form flags which are 0.5 m thick, spread out 10–20 m horizontally and run up to 80 m laterally. Both structures lie adjacent to or wrap around axons of other neurons, forming a gap of 8–10 nm. Flags and ribbons are typical for glia but have not been described previously as structures of neurons. Contralateral cells 151 appose each other in the commissures with a gap of 5–10 nm. The possible functional significance of these findings is discussed with respect to electrical coupling and to reception of strain.     

Ribosomes in thiostrepton-resistant mutants of Bacillus megaterium lacking a single 50 S subunit protein.

A protein required for the binding of thiostrepton to ribosomes of Bacillus megaterium has been purified and further characterized by immunological techniques. This protein, which does not bind the drug off the ribosome, is serologically-homologous to Escherichia coli ribosomal protein L11 and is designated BM-L11. Ribosomes from certain thiostrepton-resistant mutants of B. megaterium appear to be totally devoid of protein BM-L11 as judged by modified immunoelectrophoresis. Such ribosomes are significantly less sensitive than those from wild-type organisms to the action of thiostrepton in vitro but retain substantial protein synthetic activity. Re-addition of protein BM-L11 to ribosomes from the mutants restores them to wild-type levels of activity and thiostrepton sensitivity. Thus ribosomal protein BM-L11 is involved not only in binding thiostrepton but also in determining the thiostrepton phenotype.     

Licht- und elektronenmikroskopische Untersuchungen am Radulakomplex und zur Radulabildung vonBiomphalaria glabrata Say (=Australorbis gl.) (Gastropoda,Basommatophora)

Zusammenfassung Biomphalaria glabrata besitzt eine Prä- und eine Postradulatasche, sowie eine Sperrkutikula. Das Radulapolster besteht nicht aus Knorpel, sondern aus großen Zellen, die durch zahlreiche Vesikel, Mitochondrien, sowie durch peripher liegende Muskelfasern gekennzeichnet sind, während andere Zellen große Mengen Glykogen speichern. Die Odontoblasten sind charakterisiert durch ungewöhnlich lange Mikrovilli, die bis in die neugebildeten Radulazähne ragen. Die Zahnbildung beginnt über den hinteren Odontoblasten, die zunächst nur kurze Mikrovilli aufweisen. Das Aufrichten eines neugebildeten Zahns dürfte dadurch zustande kommen, daß die Mikrovilli länger werden. Zwischen den Mikrovilli befindet sich elektronendichtes Material, in dem Mikrofibrillen entstehen; diese dürften Chitin enthalten. Die Verflechtung der Mikrofibrillenbündel im ausgebildeten Zahn entspricht offensichtlich der komplizierten Anordnung der langen Mikrovilli während der Zahnbildung. Die Mikrovilli werden schließlich in den neugebildeten Zahn und die Radulamembran integriert. Mehrere Odontoblasten sezernieren gemeinsam einen Radulazahn. Die Radulamembran wird vorwiegend oder ausschließlich vom vordersten Odontoblasten sezerniert. Die Zellen des Deckepithels umschließen die Radulazähne; die sogenannte Sekrethöhle dürfte ein Artefakt sein. Zwischen Deckepithel und Zahn befindet sich elektronendichtes Material, das dem Zahn nicht aufgelagert wird, sondern in die Zähne eingelagert werden dürfte. Die Zellen des Basalepithels zeigen starke sekretorische Aktivität; die Sekrete dürften in Radulamembran und -zähne eingelagert werden.

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Light and electron microscopic investigations on the radula complex and radula formation ofBiomphalaria glabrata say (=Australorbis gl.) (Gastropoda, Basommatophora)

Summary Biomphalaria (Australorbis) glabrata has a preradular as well as a postradular pocket and a collostyle hood. The odontophore cartilage does not consist of cartilage, but of cells which are characterized by numerous vesicles, mitochondria, and muscle fibres in the periphery; other cells contain large amounts of glycogen. The odontoblasts are characterized by unusually long microvilli which reach into the newly formed radula teeth. The formation of a tooth begins above the posterior odontoblast which has at first only short microvilli. The tooth seems to be raised by the extension of these microvilli. Microfibrils are formed in the electron dense material which is present in the small space between the microvilli; probably these microfibrils contain chitin. Obviously the interlacing of the bundles of microfibrils in a tooth corresponds with the complex arrangement of the long microvilli during formation of the tooth. Finally the microvilli are integrated into the newly formed tooth and radular membrane. Several odontoblasts join to form a single tooth. The radular membrane is secreted mainly or exclusively by the most anterior odontoblast. The cells of the superior epithelium surround the radula teeth. The so-called secretion cavity seems to be an artifact. Electron dense material is present between teeth and superior epithelium which is not apposed to but seems to be integrated into the teeth. The cells of the inferior epithelium show considerable secretory activity; the secretions seem to be incorporated into radular teeth and membrane.

     

Algal and bacterial processes in platelet ice during late austral summer

 The biota inhabiting layers of platelet ice were investigated in the Weddell Sea during late austral summer. Due to meltwater release, the salinity of the interstitial water between platelets was reduced. Algae and bacteria accumulated within this ice environment attaining concentrations of up to 500 μg in total pigments (chlorophyll a plus phaeopigments) and 2 mg in bacterial biomass per liter. Pennate diatoms of the genus Fragilariopsis were most common in the platelet layer, while ice-free water was dominated by autotrophic nanoflagellates. Protozoa contributed only 5% or less to the total protistan (microalgae plus protozoa) cell concentration in the ice, compared to about 10% in open water, thus suggesting a low grazing pressure within the platelet habitat. The bulk of bacterial biomass occurred within the dense assemblages of pennate diatoms that grew attached to the ice platelets. Algal and bacterial concentrations in the interstitial water between platelets were much lower. Measurements of bacterial growth showed that substantial heterotrophic potential can be established within assemblages inhabiting late summer platelet ice. Small-scale analyses of bacterial activity patterns revealed that those bacteria that were closely associated with ice and/or algae showed considerably less biomass-specific substrate uptake than cells that occurred freely suspended in the interstitial water, indicating that their physiological state differed. Received: 21 October 1995/Accepted: 27 January 1996