Elektronenmikroskopischer Nachweis spezieller cytoplasmatischer Vesikel bei Micrasterias denticulata Bréb.

Summary Electronmicroscopic studies of growing and non-growing cells of Micrasterias denticulata Bréb., fixed with glutaraldehyde-OsO₄, showed a special kind of cytoplasmic vesicle which has so far not been found in other cells. These particles (1000–1200 Å in diameter) are characterized, by an unusual, multilayered membrane and a rod-like content of high electronoptic density. The vesicles are found to be accumulated in the vicinity of the nucleus and in a positional relationship to the nuclear pores. Although no evidence could be found either for a direct passage of the vesicles through the pores or for a blebbing-process from the nuclear membrane, the rod-containing vesicles could be functional in the process of nuclearcytoplasmic exchange.

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Herrn Prof. Dr. H. Drawert zum 60. Geburtstag gewidmet.

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Diese Arbeit wurde zum Teil durch ein National Science, Foundation Senior Foreign Scientist Fellowship an Dr. Oswald Kiermayer und durch einen Training Grant 5-T1-GM-707-06 an Dr. Keith R. Porter, Harvard University, unterstützt.     

Cell multiplication and ultrastructure ofMicrasterias denticulata (Desmidiaceae) grown under salt stress

Cells ofMicrasterias denticulata Bréb. were kept in nutrient solution of high osmolality (salt stress) for four weeks. In a special cell multiplication test it was established that cell division is gradually inhibited at increasing salt concentrations and totally arrested at the highest concentration (26 mosm/kg). Recovery studies proved that even cells from the highest concentration range start dividing immediately after being placed in aqua bidest. thus indicating the full reversibility of the inhibiting effect. — Cells of the highest concentration range show marked ultrastructural changes. Besides an enormous accumulation of starch and oil bodies and a condensed appearance of the ground plasma, a reduction of mitochondria, ER and the Golgi-system is found. The most striking effect occurs on the vacuolar system which appears extremely reduced and condensed. The cell wall is thickened by the formation of an additional cell wall layer with a spongy electron microscopical appearance. Through the cell wall many droplets of a probably fat-like substance are excreted. — In summary, salt stress induces growth-inhibited akinete cells in the sense ofFritsch; these can be reactivated by decreasing the salt concentration. The salt-induced akinete state seems to be an ecological adaption to unfavourable conditions rather than a degeneration of the cells.Dedicated to Prof. DrLothar Geitler on the occasion of his 90th birthday.23. 12. 1988     

Protoplasmic streaming in the giant unicellular green algaAcetabularia mediterranea

Summary Protoplasmic Streaming inAcetabularia mediteranea has been studied by microcinematography in 1. germinating zygotes, 2. germlings before the differentiation of rhizoids and apices, 3. young cells with rhizoids and apices, 4. vegetative cells-several centimeters in length, 5. cells with a maximum sized cap, containing secondary nuclei, and 6. cells after cyst formation. Intracellular transport is found to occur at a network-system of thin filaments and at a different system of headed streaming bands. At the network of filaments chloroplasts are found to move at a velocity of 1–2 m/sec. Headed streaming bands move along the filaments and may lead without interruption from the rhizoid to the apex of the cell andvice versa. The front zone of the streaming bands is occupied by a leading cytoplasmic head-structure. Small vesicles, polyphosphate granula and secondary nuclei are the predominant moving structures in headed streaming bands. The velocity of these particles is found to be 3–11 m/sec. The filament system is found during all developmental stages. Headed streaming bands are undetectable in germinating zygotes and develop from small cytoplasmic droplets in germlings to broad heavily loaded bands in the huge vegetative cell.Transport of secondary nuclei by headed streaming bands is not observed during mitotic divisions and after cyst formation, though moving bands are still present for several weeks after cyst formation.     

Cytomorphogenetic- and anti-microtubule action of the antibiotic gougerotin inMicrasterias denticulata Bréb.

Summary Differentiating cells ofMicrasterias denticulata have been treated with aqueous solutions of the antibiotic gougerotin. Strong and characteristic cytomorphogenetic aberrations, resembling those of the anuclear type of development could be observed. It has been speculated that the aberrant growth of the growing half cell is the result of inhibition of protein synthesis by gougerotin.In addition to the morphogenetic influence, nuclear migration has been strongly inhibited by the drug. Therefore, it might be suggested that gougerotin is an active anti-microtubule agent.     

Eine einfache Arbeitsweise für den Koleoptilzylindertest

Zusammenfassung Es wird eine einfache und schnell zu handhabende Arbeitsweise für den Koleoptilzylindertest zur Prüfung von Wuchsstoffen speziell in Verbindung mit papierchromatographischen Untersuchungen beschrieben. Der Test, dessen Auswertung an Hand von Kontaktkopien erfolgt, hat bei Verwendung von Indol-3-essigsaurem Natrium sein Optimum bei einer Konzentration von 10^–4% und lieferte sehr hohe Förderungswerte (120,5%).Mit 1 Textabbildung     

Maturation of Borna disease virus glycoprotein

The maturation of Borna disease virus (BDV) glycoprotein GP was studied in regard to intracellular compartmentalization, compartmentalization signal-domains, proteolytic processing, and packaging into virus particles. Our data show that BDV-GP is (i) predominantly located in the endoplasmic reticulum (ER), (ii) partially exists in the ER already as cleaved subunits GP-N and GP-C, (iii) is directed to the ER/cis-Golgi region by its transmembrane and/or cytoplasmic domains in CD8-BDV-GP hybrid constructs and (iv) is incorporated in the virus particles as authentic BDV glycoprotein exclusively in the cleaved form decorated with N-glycans of the complex type. Downregulation of BDV-glycoproteins on the cell surface, their limited proteolytic processing, and protection of antigenic epitopes on the viral glycoproteins by host-identical N-glycans are different strategies for persistent virus infections.     

Effect of selenium on thioredoxin reductase activity in Txnrd1 or Txnrd2 hemizygous mice

Thioredoxin reductase 1 (Txnrd1) and thioredoxin reductase 2 (Txnrd2) are selenoproteins whose expression and function depends on adequate supply of the trace element selenium (Se). As homozygous (-/-) knockout of both Txnrd1 and Txnrd2 is embryonically lethal, we investigated the effect of their hemizygosity (+/-) alone and in combination with dietary Se on enzymatic activity in various tissues. To assess the overall health of the corresponding mice, the growth, viability and fertility of the different experimental groups were also compared. Se depletion led to a marked decrease in Se organ contents. Se depletion was most prominent in lung, followed by liver, kidney, heart, muscle and brain. We found no major effect of Txnrd1 or Txnrd2 hemizygosity and/or Se on male fertility and the viability of offspring. A gene dose effect under Se-adequate conditions for Txnrd1 and Txnrd2 in all organs was observed. Haploid insufficiency decreased Txnrd activity to an extent that can be further decreased by Se deficiency, but not to levels below those observed for Se depletion alone. The only exception was Txnrd2 activity in kidney, heart and muscle, where we found an additive effect.