Subrepeats of rDNA intergenic spacer present as prominent independent satellite DNA in Vigna radiata but not in Vigna angularis

Subrepeats located in the rDNA intergenic spacer are also present as independently occurring, tandemly arranged satellite DNA clusters in the genome of Vigna radiata (mung bean). These 174-bp satellite repeats are identified as non-rDNA repeats by the presence of an AluI site. In the closely related Vigna angularis (adzuki bean), 174-bp repeats characterized by an AluI site occur in the rDNA with high sequence homology to the V. radiata rDNA subrepeats. A part of the 174-bp element that shows high similarity to a Xenopus terminator box (T2/T3) is slightly modified in V. angularis. However, a characteristic stem-loop structure can be formed, as in the case of V. radiata. Two highly conserved 12-bp regions occur within the 174-bp rDNA repeats of the two plants investigated. One of these 12-bp stretches exhibits some sequence identity to an element repeated twice in the 325-bp repeats in the intergenic spacer region of Vicia faba (broad bean).     

Filtration rates of mosquito larvae in suspensions of latex microspheres and yeast cells

Filtration rates of fourth instars of Aedes aegypti L., Anopheles albimanus Wiedemann, Anopheles quadrimaculatus Say and Culex quinquefasciatus Say (Diptera: Culicidae) were determined by quantifying removal rates of suspended latex microspheres or yeast cells. Average filtration rates were 33–34 l/larva/h (An. quadrimaculatus), 49–55 (An. albimanus), 490–590 (C. quinquefasciatus) or 590–690 l/larva/h (Ae. aegypti) for larvae exposed to latex beads suspended in phagostimulant yeast extract solutions. In suspensions of yeast cells, filtration rates of Ae. aegypti and C. quinquefasciatus were not significantly different from filtration rates in latex bead suspensions. Larval density, ranging from 0.3 to 2.4 individuals/ml in tests with Ae. aegypti and C. quinquefasciatus and up to 4.8 larvae/ml in tests with Anopheles, did not influence filtration rates.

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Zusammenfassung Die Filtrierraten von Viertlarven der Stechmückenarten Aedes aegypti, Anopheles albimanus, Anopheles quadrimaculatus und Culex quinquefasciatus wurden in Laborversuchen bestimmt. Dabei wurde die Filtrierrate definiert als ein Wasservolumen, welches pro Stunde von einer Larve von den Testpartikeln (Hefezellen oder Latexkugeln mit einem Durchmesser von 2 m) befreit wurde. Nach Exposition der Larven in Dichten zwischen 0.15 und 2.4 Larven/ml (Ae. aegypti und C. quinquefasciatus), oder zwischen 0.6 und 4.8 Larven/ml (Anopheles) wurde der Partikelgehalt der Suspensionen in einem elektronischen Partikelzähler bestimmt. Die Filtrierraten wurden über die Verringerung der Partikeldichte mit zunehmender Larvendichte entsprechend einer in der Literatur angegebenen Formel berechnet.Suspensionen von Hefezellen wurden von Ae. aegypti Larven mit einer Leistung von 680±220 l/Larve/h gefiltert. Bei Larven von C. quinquefasciatus wurden Filtrierraten von 600±120 l/Larve/h gemessen. Die Filtrierraten beider Arten waren unabhängig von der Larvendichte. In Suspensionen von Latexpartikeln (zur Phagostimulation der Larven wurden diese Partikel in Lösungen von Hefeextrakt angeboten) wurden die folgenden Filtrierraten festgestellt: An quadrimaculatus: 33–34, An. albimanus: 49–55, C. quinquefasciatus: 490–590, und Ae. aegypti: 560–690 l/Larve/h. Die Larvendichte hatte auch hier keinen Einfluss auf die Filtrierrate. Hefezellen und Latexpartikel wurden von Ae. aegypti und C. quinquefasciatus mit statistisch nicht signifikant verschiedenen Filtrierraten aufgenommen. Die Filtrierraten der Anopheles Larven waren um mehr als eine Zehnerpotenz kleiner als die Filtrierraten von Culex und Aedes, und auch untereinander signifikant verschieden. Der Einfluss der Filtrierraktivität von Stechmückenlarven auf das Seston der Brutgewässer wird diskutiert.

     

1-Methylguanine and 7-methylguanine increase cell agglutinability

Summary 1-Methylguanine and 7-methylguanine, both metabolic products of tRNA degradation, are known to induce transformation of Chinese hamster fibroblasts in culture. The effects of these compounds on the cell membrane have been studied by the method of Concanavalin A-mediated hemadsorption. 1-Methylguanine or 7-methylguanine induced a 50% increase of Con A-mediated hemadsorption within 20 hours of exposure of the cells to the agent at a concentration of 10^-5 M. This alteration was reversed within 13 days when the cells were grown in the control medium. Prolonged treatment with 1-methylguanine or 7-methylguanine resulted in changes which were only slowly reversed during growth of the cells in the control medium. The effect of the methylated purines on the cell membrane could be completely inhibited by simultaneous addition of dibutyryl-cAMP at a concentration of 10^-5 M. The possible mechanism of cell membrane alteration by methylated purines and its relevance to transformation in vitro are discussed.     

Comparison of the ribosomal RNA genes in four closely relatedCucurbitaceae

Cucurbitaceae are characterized by a high copy number for nuclear ribosomal RNA genes. We have investigated the genomic ribosomal DNA (rDNA) of four closely related species of this family with respect to structure, length heterogeneity, and evolution. InCucumis melo (melon) there are two main length variants of rDNA repeats with 10.7 and 10.55kb.Cucumis sativus (cucumber) shows at least three repeat types with 11.5, 10.5, and 10.2kb.Cucurbita pepo (zucchini) has two different repeat types with 10.0 and 9.3kb. There are also two different repeat types inCucurbita maxima (pumpkin) of about 11.2 and 10.5kb. Restriction enzyme mapping of the genomic rDNA of these four plants and of cloned repeats ofC. sativus shows further heterogeneities which are due to methylation or point mutations. By comparison of the restriction enzyme maps it was possible to trace some evolutionary events in the family ofCucurbitaceae. Some aspects of regulation and function of the middle repetitive rRNA genes (here between 2000 and 10000 copies) are discussed.     

A rapid cell membrane permeability test using flourescent dyes and flow cytometry

A reliable and rapid test to detect cytotoxic chemicals which affect cell membranes is described. Fluorescein diacetate freely penetrates intact cells where it is hydrolyzed to its fluorochrome, fluorescein, which is retained in the cell due to its polarity. On the other hand, ethidium bromide is known to be excluded from the intact cell, staining only nucleic acids of membrane-damaged cells. The combination of both fluorochromes results in counter-staining: intact cells fluoresce green (cytoplasm) and membrane-damaged cells fluoresce red (nucleus and RNA). Rat thymocytes freshly isolated without enzyme treatment were incubated simultaneously with test substance and dye solution fluorescein diacetate and ethidium bromide. A two-parameter analysis was performed on a flow cytometer with an on-line computer. Concentration-dependent effects of various detergents and solvents were quantified by measuring the amount of dye retention, i.e., the decrease or increase in fluorescein—fluorescence (peak shift), and the decrease in dye exclusion (increase in ethidium bromide-staining) relative to the untreated control. The assay can be used for rapid monitoring of chemical insults to cell membranes which precede the decrease of the viability measured by pure dye exclusion techniques.Abbreviations DMA dimethyl sulfate - DMSO dimethyl sulfoxide - EB ethidium bromide - F fluorescein - FDA fluorescein diacetate - FS₂₅ concentration of test substance resulting in a F-peak left-shift of 25% from control - PBS phosphate buffered saline - SCT forward light scatter - SDS sodium dodecyl sulfate     

Thymus-independent induction and antigen-dependent recovery of idiotype-specific suppression

BALB/c nude (nu/nu) mice and euthymic (nu/+) littermates were treated as neonates with anti-T15 antibody and challenged at various ages with either a thymus-independent, PC-Brucella abortus (PC-BA), or thymus-dependent, PC-keyhole limpet hemocyanin (PC-KLH), form of phosphorylcholine (PC). Nu/nu mice challenged with PC-KLH received KLH-primed splenic T cells prior to immunization. Neither neonatally anti-idiotype-treated nu/+ nor nu/nu mice responded with the production of T15-positive anti-PC antibodies after challenge with either form of PC antigen. It is concluded that neither induction nor maintenance of a state of T15-specific suppression requires thymus-matured T cells. Recovery of anti-PC responsiveness in suppressed nu/+ or nu/nu mice was similar and was found to be related to the form of antigen used to elicit the response. Immunization with PC-KLH revealed a long-lasting unresponsiveness (up to 16 weeks). In contrast, immunization with PC-BA elicited a full anti-PC response as early as at 6.5 weeks of age.     

Fine structural and enzyme histochemical observations on the dorsal tail tubercle of Mertensiella caucasica (Urodela,Amphibia)

Summary Dorsal tubercle and skin of Mertensiella caucasica have been investigated with the electron microscope and enzyme histochemical methods. The epidermis of the tubercle consists of 8–9 cell layers, that of normal dorsal skin of 5–6. The tubercle is filled with large mucous glands which are surrounded by an almost complete layer of smooth muscle cells (myoepithelial cells). Their glandular cells undergo cyclical changes and are characterized by specific secretory granules, which differ from those of the relatively small mucous glands of the normal dorsal skin.In the connective tissue of the tubercle a relatively rich supply of nerve fibres has been found, which in part contain synaptic and dense core vesicles or accumulations of mitochondria. In the normal dorsal skin nerve fibres occur less frequently.The following enzymes have been demonstrated in the mucous glands of the tubercle: SDH, acid phosphatase, unspecific esterases, E 600 resistant esterase.The tubercle seems to stimulate the female cloaca chemically and mechanically.     

Fundamentals of an applied ecosystem research project in the Wadden Sea of Schleswig-Holstein

The aims, content, and organisatory structure of a proposed interdisciplinary ecosystem research project in the Wadden Sea of Schleswig-Holstein (W. Germany) are briefly presented. The project will include research on both fundamental as well as applied aspects of the Wadden Sea ecosystems and their interaction with local human activities. In contrast to most of the other completed or currently running ecosystem research projects on tidal coasts, a considerable part of the scientific work will also deal with aspects of ecosystem management and protection of the various marine and semiterrestrial habitats of the Wadden Sea. Considerable attention is paid to theoretical and methodological aspects of research on ecosystems and landscape units. In particular, the adoption of a hierarchical view of complex biological and environmental systems is recommended. Presented at the VI International Wadden Sea Symposium (Biologische Anstalt Helgoland, Wattenmeerstation Sylt, D-2282 List, FRG, 1–4 November 1988)