Effects of temperature on cytomorphogenesis and ultrastructure ofMicrasterias denticulata Bréb

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.Dedicated to my teacher Professor Oswald Kiermayer in deep gratitude     

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.     

Local accumulation of membrane-associated calcium according to cell pattern formation inMicrasterias denticulata,visualized by chlorotetracycline fluorescence

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.     

Lateral hydrodynamic effects of rotating cytoskeletal components as possible determining factors for cytomorphogenesis in plant cells

Summary Rotating filaments produce far reaching lateral streams in a thick medium and localized negative pressure when placed adjacent a wall. Freely movable filaments can roll on a wall. Pairs of counterrotating filaments are stabilized. When rotating components of the cytoskeleton generate these lateral hydrodynamic effects many hitherto mysterious features can be explained, including positioning of organelles and morphogenesis of plant cells. It is postulated that MTs and MFs roll laterally to positions of equilibrium, these being, for example, the preprophase band site and the cortical site that controls local thickening of the secondary wall. The orientation of microfibrils in the cell wall may also depend on the lateral effects of rotation. Different streaming patterns can move and shape the nucleus and other organelles and bring them in appropriate positions. Morphogenetic events as septum and lobe formation in desmids could result. Time-dependent reversal of the rotational directions are required for the transformation of the patterns.Dedicated to the memory of my friend and fellow student Oswald Kiermayer     

Elektronenmikroskopische Untersuchungen zum Problem der Cytomorphogenese vonMicrasterias denticulata Bréb.

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.

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Formation and ultrastructure of the primary wall ofMicrasterias denticulata Bréb. under the influence of cycloheximide

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.

Die Untersuchungen wurden vom Fonds zur Förderung der wissenschaftlichen Forschung (Projekt Nr. 2783, 3660) unterstützt; Frau Ing.Doris Pinegger danken wir für die technische Hilfe.