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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Plant systematics and evolution 164 (1989), S. 197-208 
    ISSN: 1615-6110
    Keywords: Algae ; Chlorophyta ; Desmidiaceae ; Micrasterias ; Ultrastructure ; electron microscopy ; cell multiplication ; salt stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract 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.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1615-6102
    Keywords: Ca2+ accumulation ; Membrane differentiation ; Chlorotetracycline ; Cytomorphogenesis ; Micrasterias
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Developing cells ofMicrasterias denticulata Bréb. show a characteristic fluorescence of the plasma membrane (or cortical protoplasm) after treatment with chlorotetracycline (CTC), which is known to be an indicator for membrane-bound Ca2+. Depending on the stage of development the fluorescing sites of the young half cell are distributed in a specific pattern which corresponds to cell pattern formation. Therefore growth and thus cytomorphogenesis inMicrasterias seem to be mediated by a patterned accumulation of Ca2+ at the periphery of the differentiating cell. Participation of Ca2+ in a membrane-recognition process responsible for local vesicle incorporation is discussed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 112 (1982), S. 138-141 
    ISSN: 1615-6102
    Keywords: Ca2+ accumulation ; Pore formation ; Membrane recognition ; Chlorotetracycline ; Micrasterias
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary During the stage of pore formation developing cells ofMicrasterias denticulata show a patterned distribution of fluorescent dots on the plasma membrane after treatment with chlorotetracycline. The center-to-center spacing of these dots corresponds with the distances between the individual cell wall pores ofMicrasterias. Therefore it is supposed that the patterned distribution of pores and their formation which is mediated by special “pore vesicles” are related to local accumulations of membrane-associated Ca2+. Membrane-associated Ca2+ seems not only to be functional in tip growth but to be a general mediator for recognition and fusion processes between various vesicles and the plasma membrane.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1615-6102
    Keywords: Cell shape formation ; Mutant ; Ca2+-distribution ; Cycloheximide ; Micrasterias
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cell development and ultrastructure are studied in the defect mutant cellMicrasterias thomasiana f. uniradiata which lacks cell pattern at one side of the cell. The ultrastructural studies reveal an uneven distribution of vesicles, preponderating at the normally growing side of the cell, as well as the presence of a special kind of dark vesicles. By means of turgor reduction and treatment with chlorotetracycline and cycloheximide some processes involved in cell shape formation are pointed out and are compared with those already described for biradiateMicrasterias cells. It is demonstrated that the asymmetric cell shape of the mutant cell is already determined at the early stage of bulb formation and is due to a unilateral growth during the later stages of development. The asymmetric arrangement of the growth areas during cell development of the mutant is expressed by an asymmetric distribution of primary wall accumulations induced by turgor reduction as well as by the presence of fluorescence zones after treatment with the Ca2+ -chelate probe chlorotetracycline at only one side of the cell. Inhibition of protein synthesis by cycloheximide during cell growth of the mutant leads to the formation of a characteristically reduced cell pattern (“anuclear type of development”) similar to that ofMicrasterias denticulata andMicrasterias thomasiana under the same conditions. Nevertheless, this cell pattern develops at only one side of the cell, indicating that the mutant does not have any information for cell pattern formation at the defective side.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 126 (1985), S. 74-90 
    ISSN: 1615-6102
    Keywords: Nuclear migration ; Microtubules ; Microtubule center ; Membranes ; Micrasterias
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Nuclear migration and the spatial arrangement of the participating microtubules are studied inMicrasterias thomasiana and in the defect mutant cellMicrasterias thomasiana f. uniradiata. In both of these cell types the two microtubule systems, the “posttelophase system of MT” (PTS) and the “isthmus system of MT” (IS)—which are known to be involved in nuclear migration and anchoring from earlier studies onMicrasterias denticulata—are present in the vicinity of the nucleus. In the mutant cell, however, the orientation of these two MT systems as well as their MT arrangement differ from those in the normalMicrasterias cells. Nuclear migration in the mutant is characterized by a turn of the nucleus and the associated PTS around one of the isthmus invaginations of the cell while in the normalMicrasterias cells it occurs as a straight-lined motion along the longitudinal axis of the cell. The results indicate that the reduction of cell pattern inMicrasterias caused by mutation is attended by a disoriented establishment of the cytoskeleton involved in nuclear migration. From comparison of the nuclear behavior and the MT arrangement in the mutant with that of the normalMicrasterias cells further information on the mechanism of nuclear migration inMicrasterias is obtained. It is suggested that interactions between the microtubule center (MC), the nuclear envelope and areas of the plasma membrane are functional in the formation, orientation and localization of the nucleus associated microtubule-microfilament complex.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1615-6102
    Keywords: Anti-microtubule action ; Cytomorphogenesis ; Micrasterias ; Protein synthesis inhibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: 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.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 157 (1990), S. 1-2 
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 157 (1990), S. 3-18 
    ISSN: 1615-6102
    Keywords: Chilling ; Cytomorphogenesis ; Heat ; “Heat shock granules” ; Micrasterias ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Exposure of growingMicrasterias cells to high (32°–36°C) and low (3°–10°C) temperatures produces changes in morphology that are accompanied by several ultrastructural alterations. Whereas low temperatures essentially cause simplification of cell ornamentation, a variety of cell malformations result from high temperature treatment. These are the loss of cell symmetry leading to markedly aberrant cell shapes and an increase of “main lobes” with reduced degree of differentiation. Preliminary studies indicate that a shift in the distribution of membrane-associated Ca2+ by elevated temperatures probably underlies these abnormal cytomorphogenetic events. Both, low and high temperature cause a reduction in size of the young half cell and affect cytoplasmic streaming. Moreover, nuclear migration is retarded and chloroplast arrangement is influenced by temperature treatment at both ranges. Growth velocity of primary wall responsible for cell shaping is increased at high and slowed down at low temperatures compared to cells grown at 20°C. The main ultrastructural alterations induced by high temperatures are an increase in amount and length of ER cisternae, the appearance of “heat shock granule” aggregations localized in the cytoplasm, a reduced number of ribosomes and polysomes, the presence of oil bodies in growing cells and a varying thickness of the primary wall. Influences of low temperatures on ultrastructure are less pronounced. They are manifested in the formation of large aggregations of ER cisternae slightly differing from those found in untreated cells, a disturbed arrangement of the microtubule system surrounding the nucleus and a decrease of the number of cell wall forming cytoplasmic vesicles. It is thought that most of the temperature effects are due to an influence on membranes probably an alteration of ionic currents and, in addition, a modulation of normal protein synthesis.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 103 (1980), S. 169-177 
    ISSN: 1615-6102
    Keywords: Cell wall ultrastructure ; Cycloheximide ; Cytomorphogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung Die Wirkung einer Blockade der Proteinsynthese durch Cycloheximid wurde an sich differenzierenden Zellen vonMicrasterias denticulata Bréb. licht- und elektronenmikroskopisch sowie mikrokinematographisch untersucht. Es wurde der Befund vonTippit andPickett-Heaps (1974) bestätigt, daßMicrasterias-Zellen unter dem Einfluß von Cycloheximid eine abnorme Zellentwicklung zeigen, die sich in einer Vereinfachung des Zellmusters und einem blasigen Anschwellen der Lappen äußert („anucleate type of development“). Die Primärwand Cycloheximid-behandelter Zellen weist eine markante Änderung ihrer Ultrastruktur auf. Und zwar finden sich diskrete Partikel, bei denen es sich mit großer Wahrscheinlichkeit um die Inhalte von D-Vesikel (Kiermayer 1970) handelt, in einer eigenen zusätzlichen Schicht an die homogene Primärwandschicht angelagert. Es wird angenommen, daß durch die Hemmung der Proteinsynthese während der Zellentwicklung D-Vesikelinhalte ihre Fähigkeit verlieren, sich in die wachsende Primärwand einzulagern. Ein möglicher Zusammenhang dieses Phänomens mit der Entstehung der typischen Zellmißildungen wird diskutiert. Die Bildung einer Sekundärwand wird durch Cycloheximid verhindert.
    Notes: Summary The effect of a blockade of protein synthesis by cycloheximide on differentiating cells ofMicrasterias denticulata Bréb. has been studied by light- and electronmicroscopy and microcinematography. The result ofTippit andPickett-Heaps (1974) thatMicrasterias cells, treated with cycloheximide show an abnormal cell development, e.g., reduction of the cell pattern and a bladderlike swelling of the lobes (“anucleate type of development”) could be supported. The primary wall of cycloheximide treated cells shows a striking change of its ultrastructure. Many discrete particles very probably representing the content of D-vesicles (Kiermayer 1970) form a separate additional inner layer near the outer homogenous layer of the primary wall. It is suggested that during an inhibition of protein synthesis the content of D-vesicles looses its ability to be incorporated into the growing cell wall. A possible connection of this phenomenon with the typical malformation of the cell is discussed. The formation of a secondary wall is prevented by cycloheximide.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1615-6102
    Keywords: Dictyosomes ; Golgi vesicles ; Micrasterias ; Morphogenesis ; Vesicle fusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two different types of Golgi vesicles involved in wall formation can be visualized during lobe growth inMicrasterias when using high-pressure freeze fixation followed by freeze substitution. One type that corresponds to the “dark vesicles” (DV) described in literature seems to arise by a developmental process occurring at the Golgi bodies with the single vesicles being forwarded from one cisterna to the next. The other vesicle type appears to be produced at thetrans Golgi network without any visible precursors at the Golgi cisternae. A third type of vesicle, produced by median andtrans cisternae, contains slime; these are considerably larger than those previously mentioned and they do not participate in wall formation. The distribution of the two types of cell wall vesicles at the cell periphery and their fusion with the plasma membrane are shown for the first time, since chemical fixation is too slow to preserve a sufficient number of vesicles in the cortical cytoplasm. The results indicate that fusions of both types of vesicles with the plasma membrane are possible all over the entire surface of the growing half cell. However, the DVs are much more concentrated at the growing lobes, where they form queues several vesicles deep behind zones on the plasma membrane thought to be specific fusion sites. The structural observations reveal that the regions of enhanced vesicle fusion correspond in general to the sites of calcium accumulation determined in earlier studies. By virtue of the absence of the DVs in the region of cell wall indentations the second type of wall forming vesicle appears prominent; they too fuse with the plasma membrane and discharge their contents to the wall.
    Type of Medium: Electronic Resource
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