E. Schnepf

The fluorochrome, calcofluor white, binds oriented to structural polysaccharide fibrils

SummaryThe parallel oriented cellulose microfibrils of the bristles ofAcanthosphaera zachariasi show difluorescence after staining with the fluorochrome calcofluor white ST. This dye thus is adsorbed oriented parallel to the microfibrillar longitudinal axis.

Side branch formation and orientation in the caulonema of the moss,Funaria hygrometrica: Normal development and fine structure

SummaryThe regular branching of theFunaria caulonema filaments is partly related to rhythms in nuclear and cell division. The formation and development of the branches were studied by light and electron microscopy with particular attention directed to the distribution of microtubules and the polar organization of the cytoplasm. The new side branch breaks through the wall of the mother cell. The site of branch development is determined by the position of the nucleus of the mother cell. In protonemata which grow in vertically placed Petri dishes gravity influences the position of nuclei and side branches, and also the direction of oblique cross walls in the caulonema filaments to a certain extent.

The tip-to-base calcium gradient in pollen tubes ofLilium longiflorum measured by proton-induced X-ray emission (PIXE)

SummaryThe intracellular calcium distribution in pollen tubes ofLilium longiflorum was measured by proton-induced X-ray emission (PIXE) with the Heidelberg proton microprobe, which is a new method for biological application. Studies by electron-induced X-ray emission (EIXE) were done in comparison. Independent of the preparation technique, the pollen tubes show a tip-to-base calcium gradient. The shape of the calcium gradient and the total calcium content depend on the preparation technique. The calcium ionophore A-23187 destroys the calcium gradient and leads to a loss of most cell calcium. Chlorotetracycline (CTC) treatment increases the amount of membrane-bound calcium.

A cytokinin-sensitive mutant of the moss,Physcomitrella patens, defective in chloroplast division

SummaryAn X-ray induced mutant (PC22) of the moss,Physcomitrella patens was analysed with respect to its morphology, physiology and suitability for microculture techniques. The mutant protonemata are defective in bud formation and in chloroplast division. As a consequence of the latter, giant chloroplasts are formed which disturb the development of the phragmoplast, the formation of regular cross walls, and cell division. Abnormal cross walls are rich in callose. The actin cytoskeleton was found to be less regularly developed in the mutant than in the wild type. Three-dimensional analysis of the microtubular arrangement with confocal laser scan microscopy demonstrates a close association between spindle- or phragmoplast- and “interphase”-microtubules. The deficiencies in chloroplast division and in bud formation can partly be compensated for by exogeneously applied cytokinin. The suitability of this particular developmental mutant for further studies was shown by regeneration of protoplasts in microculture and microinjection of the fluorochrome Lucifer yellow into the chloroplast.

Gymnodinium aeruginosum (Dinophyta): A blue-green dinoflagellate with a vestigial, anucleate, cryptophycean endosymbiont

Gymnodinium aeruginosum has the usual fine structure of a dinoflagellate but does not seem to contain a well elaborated peduncle or a microtubular basket. Naked cells are surrounded by a single large amphiesmal vesicle. It houses an endosymbiont with typical blue-green cryptophycean chloroplasts (generally only one), cryptophycean starch grains in the periplastidal cytoplasm without a nucleomorph, and two membranes separating the periplastidal cytoplasm from the cryptophycean cytoplasm which contains mitochondria, ER, vesicles and ribosomes, but no eukaryotic nucleus. The endosymbiont is surrounded by a single membrane. Possible ways of the acquisition of the endosymbiont and the problem of the existence of ribosomes within a compartment without nucleus are discussed.

Side branch formation and orientation in the caulonema of the moss,Funaria hygrometrica: Experiments with inhibitors and with centrifugation

SummaryColchicine treatment ofFunaria caulonemata, usually does not inhibit initiation of a side branch or its incipient elongation but does prevent movement of chloroplasts and the nucleus into the outgrowth. After colchicine and after cytochalasin B treatment side branches are formed about at the normal age of the cells; because of the inhibition of the apical cell they arise at an abnormal position,i.e., not in the third but in the second cell of a filament. After D2O treatment the organelles are dislocated toward the basal cross wall. The site of side branch formation is then obviously determined by the position of the nucleus. Cells with an irreversibly reversed longitudinal polar axis can be found; by centrifugation in proximal direction the sites of side branch initiation likewise are displaced into the proximal region of the cell, especially if the remigration of the nucleus is inhibited by colchicine. High concentrations of Ca2+ ions induce the formation of “side branch cells”, without any outgrowth. The calcium ionophore A 23 187 influences the position of the nucleus and of the side branch only slightly. After these various treatments intercalary divisions frequently occur. The role and interrelationship of the nucleus and peripheral cytoplasm in establishing and maintaining the polar axes, and the role of microtubules are discussed.

Mikrotubulus-Anordnung und -Umordnung, Wandbildung und Zellmorphogenese in jungenSphagnum-Blättchen

SummarySphagnum leaflets develop by very regular, equal and (later on) unequal divisions which both are exclusively anticlinal. In non-dividing cells the microtubules (MT) are connected with the plasmalemma; at the inner walls they run parallel (anticilinally), at the outer walls they are dispersed. In preprophase they are concentrated in a preprophase band, during mitosis in the spindle and in the phragmoplast, and after cytokinesis in a “postcytokinetic layer” along the young wall. Their regular distribution allows some rough quantitative estimations. Their total length per cell is about 500–900 μm in interphase, 1000 μm in preprophase, about or a little more than 1000 μm in the spindle and presumably also in the phragmoplast, and about 500 μm in postcytokinesis. Between some of these stages their amount descreases drastically. The validity and meaning of these data are discussed: the MT are redistributed mainly by disaggregation and reaggregation rather than by displacement though sometimes a movement in the direction of their axis may also occur. Their arrangement at the young cell wall, at the developing wall thickenings in the hyalocytes and at certain extraordinarily elongating wall zones favour the idea that they function mainly as cytoskeletal elements which are involved in wall formation and cell morphogenesis. It is suggested that they may allow a localized thickening of a wall by lifting off the plasmalemma from the wall against the turgor pressure to form an extraplasmatic space in which wall material (at first Golgi apparatus-derived) is accumulated.ZusammenfassungSphagnum-Blättchen entwickeln sich durch sehr regelmäßige äquale und (später) inäquale Teilungen, die stets antiklinal sind. In sich nicht teilenden Zellen sind die Mikrotubuli (MT) mit dem Plasmalemma verbunden; sie laufen an den Innenwänden parallel (antiklinal), an den Außenwänden in Streutextur. In der Präprophase sind sie in einem Präprophaseband konzentriert, während der Mitose in der Spindel und im Phragmoplast und nach der Zellteilung in einer „Postcytokinese-Lage” an der jungen Wand. Ihre regelmäßige Anordnung ermöglicht einige ungefähre quantitative Abschätzungen. Ihre Gesamtlänge pro Zelle beträgt etwa 500–900 μm in der Interphase, 1000 μm in der Präprophase, etwa 1000 μm (oder ein wenig mehr) in der Spindel und vermutlich auch im Phragmoplast und etwa 500 μm in der Postcytokinese. Zwischen einigen von diesen Stadien ist ihre Menge stark verringert. Die Gültigkeit und die Bedeutung dieser Befunde wird diskutiert. Die MT werden hauptsächlich durch Ab- und Wiederaufbau umgeordnet und wahrscheinlich nicht durch Verlagerung, obwohl sie sich möglicherweise manchmal auch in Längsrichtung bewegen. Ihre Verteilung an der jungen Wand, an den sich entwickelnden Spangen in den Hyalinzellen und an einigen sich besonders stark streckenden Wandzonen spricht dafür, daß sie hauptsächlich als Cytoskelett-Elemente dienen, die an der Wandbildung und Zellmorphogenese beteiligt sind. Möglicherweise bilden sie lokale Wandverdickungen dadurch, daß sie das Plasmalemma von der Wand — gegen den Turgor — abheben und einen extraplasmatischen Raum schaffen, in dem Wandmaterial (zuerst aus dem Golgi-Apparat) akkumuliert wird.

Associations between membranes and microtubules during mitosis and cytokinesis in caulonema tip cells of the mossFunaria hygrometrica

SummaryThe interphase nucleus in theFunaria caulonema tip cells is associated with many non-cortical microtubules (Mts). In prophase, the cortical Mts disappear in the nuclear region; in contrast to moss leaflets, a preprophase band of Mts is not formed in the caulonema. The Mts of the early spindle are associated with the fragments of the nuclear envelope. Remnants of the nucleolus remain in the form of granular bodies till interphase. The metaphase chromosomes have distinct kinetochores; the kinetochore Mts are intermingled with non-kinetochore Mts running closely along the chromatin. Each kinetochore is associated with an ER cisterna. ER cisternae also accompany the spindle fibers in metaphase and anaphase. In telophase, Golgi vesicles accumulate in the periphery of the developing cell plate where no Mts are found. The reorientation of the cell plate into an oblique position can be inhibited by colchicine. It is concluded that the ER participates in controlling the Mt system, perhaps via calcium ions (membrane-bound calcium ions have been visualized by staining with chlorotetracycline) but that, on the other hand, the Mt system also influences the distribution of the ER. The occurrence and function of the preprophase band of Mts is discussed.

The flagellar root apparatus, the microtubular system and associated organelles in the chrysophycean flagellate,Poterioochromonas malhamensis Peterfi (syn.Poteriochromonas stipitata Scherffel andOchromonas malhamensis pringsheim)

SummaryThe two flagella ofPoterioochromonas are inserted in an apical platform which is shaped by six long flagellar root fibres. The arrangement and structure of these root fibres are described in detail. One of these fibres is the single nucleating site for cytoplasmic interphase microtubules which extend peripherally down to the cytoplasmic tail. Another fibre proceeds toward the centre of the cell and passes the nucleus but is different in structure, position and function from the striated rhizoplast found in many chrysophycean flagellates which is observed but vestigial inPoterioochromonas.A specific kinetosomal mitochondrion has a threefold attachment to the flagellar root apparatus. The chloroplast is also bound to the root system. It has no stigma, but a special continuation of the periplastidial cisterna is developed instead. Another cisterna extends from the nuclear envelope-dictyosome interspace to the kinetosome of the long flagellum. The functional and taxonomic meanings of these structures and of their mutual arrangement are discussed. It is concluded that the present strain (no. 933-1 a of the Collection of Algal Cultures at the Institute of Plant Physiology, Göttingen) has to be excluded from the genusOchromonas.

Influence of the herbicide oryzalin on cytoskeleton and growth ofFunaria hygrometrica protonemata

SummaryProtonemata ofFunaria hygrometrica were exposed to the herbicidal MT inhibitor oryzalin. A reduction of the growth rate together with a disturbance of oriented polar growth is observed. Both effects are reversible. Visualization of MT by IFT reveals differential sensitivities of MT. At lower concentrations (⩽10−6 M) only the cytoplasmic MT are depolymerized causing impairment of the migration of the nucleus and the transport of the plastids. Close association of MT with the surface of the plastids is demonstrated. At higher concentrations of oryzalin spindle and phragmoplast MT are affected as well. They are found in unusual orientations and display a variety of aberrant forms like multipolar spindles or the occurrence of several “mini-spindles” within one cell. The mode of action of oryzalin is discussed and the necessity of a continuous network of cytoplasmic MT between nucleus and growing tip for the maintenance of polar growth is emphasized.