F. Poli

Effects of Congo red on wall synthesis and morphogenesis in Saccharomyces cerevisiae

Abstract Congo red, a stain which prevents polyglycan microfibril assembly, was assayed on growing cells of Saccharomyces cerevisiae. In the presence of 0.25 mg/ml of the chemical, yeast developed aberrant wall thickenings and malformed septa, and underwent several budding events without the occurrence of the separation between mother and daughter cells. It is suggested that Congo red may uncouple polymerization and crystallization of the wall constituents, primarily chitin, that normally form microfibrils. It is also propsed that the regular assembly of the chains into microfibrils is needed to give a correct rate and direction to the process of polyglycan synthesis.

Morphological anomalies induced by Congo red in Aspergillus niger

Aspergillus niger germ tubes were exposed for 6 h to 0.15 mg/ml of Congo red, a stain which prevents chitin microfibril assembly. The most evident alterations, detected under ultraviolet light and by transmission and scanning electron microscopy, concerned the hyphal tips which burst or, most frequently, expanded into bulges. In the latter structures, new hyphal tips appeared which, after giving rise to more or less developed hyphae, were themselves converted into new bulges. Therefore, segments derived from isotropic and polarized growth alternated in the organisms exposed to the dye.An interpretation of these abnormalities is advanced based upon the assumption that the maintainance of a regular gradient of wall viscosity in the hyphal extension zone depends primarily on the capability of glycan chains to form crystalline aggregates of increasing complexity.

Cytoskeletal structures inEuglena gracilis after triton X-100 extraction and dry cleaving

SummaryA three-dimensional network of structural filaments was visible with common electron microscopes in the cytoplasm ofEuglena gracilis green cells extracted with buffers containing the nonionic detergent Triton X-100. A similar filamentous web was detected at the periphery of critical point dried cells cleaved on grids by means of an adhesive tape. SDS-polyacrylamide gel electrophoresis of the detergent-resistent cytoskeleton showed that actin or actin-like proteins of molecular weight in the range of 43–45 K are not among the components having a structural role inEuglena. The significance of these findings was discussed in relation to the capability of the alga to change the cell shape.

Callus Formation, Cell Suspension Culture and Plant Regeneration in Ranunculus serbicus Vis.

Summary A procedure is described for the regeneration of whole plants of Ranunculus serbicus Vis. from cell suspension cultures through somatic embryogenesis. The best response for callus induction and growth was obtained from petioles on Murashige and Skoogs medium (MS) with hormones. Two different types of calli were obtained: (i) a friable white-yellow and fast growing callus with naphthaleneacetic acid (NAA) and benzyladenine (BA) and (ii) a compact, yellow-brown and slow growing callus with 2,4- \dichlorophenoxyacetic acid (2,4-D) and BA or kinetin (KIN). Cell suspension cultures arised from friable calli kept in liquid MS plus NAA and BA. They contained both single, vacuolated, non-embryogenic cells and densely cytoplasmic cell aggregates having the ultrastructural characteristics of embryogenic cells. Somatic embryos developed from most of the cell clusters plated on agarised MS plus NAA and BA or 2,4-D and KIN. When embryoids from NAA+BA containing MS media were transferred onto MS (half-strength of salt solution) without hormones, they developed plantlets that became mature plants.

Anomalous Morphogenetic Events in Yeasts Exposed to the Polysaccharide-Binding Dye Congo Red

SUMMARYWhen exposed to Congo red, Rhodotorula glutinis halts cell proliferation, whereas Saccharomyces cerevisiae continues to bud; however, the separation between mother and daughter cells is impeded. Both yeasts develop diverse wall and septum abnormalities due to the accumulation of amorphous materials instead of chitin microfibrils. In Saccbaromyces, the original wall frequently breaks and numerous vesicles, probably of a secretory nature, are visible in the cytoplasm. The microorganisms employed react differently to Congo red exposure due to the different roles that chitin plays in their walls. To explain why Congo red forces chitin synthase to form excessive amounts of N-acetylglucosamine chains with a random distribution, a model is proposed in which multienzyme complexes dissociate into single units since the polymers under synthesis, with the dye attached, can not assemble regularly. Each enzyme subunit continues to form glucan chains while it moves freely and randomly along the plasma membrane.

Effect of Congo Red On Yeast Morphogenesis

Valuable information about fungal morphogenesis can be gained by treating the cells with agents that vary the mode in which the wall components are synthesized and/or deposited. In yeasts, chitin, a structural polysaccharide responsible for fundamental morphogenetic events, is synthesized by enzyme complexes inserted in the plasma membrane (1). However, this structure, when studied by means of freeze etching and freeze fracturing, did not reveal aggregates of particles interpretable as the site of chitin synthesis (2). In any case, it is generally assumed that each enzyme complex is composed of as many units as are necessary to form the chains that, in the periplasmic space, stack into a crystalline microfibril (3).

Production of protoanemonin by cell suspension cultures of Ranunculus serbicus Vis.

Summary Cell suspension cultures of Ranunculus serbicus obtained from petiole explants are producing protoanemonin. The biosynthetic rates depend on illumination as well as on the time of cultivation. This is the first report protoanemonin production in cell cultures.

Alterations induced by dimethyl sulfoxide inEuglena gracilis with emphasis on the side effects

SummaryIn a previous study, we demonstrated that 5% dimethyl sulfoxide (DMSO) alters the contractile system responsible for cell motility (euglenoid movements) and cytokinesis inEuglena gracilis. However, the nucleus continued to divide and most cells were larger than normal and binucleated.The present study reveals that DMSO, besides altering the cell functions requiring microfilaments, also affects other cell parts. More precisely, the materials normally covering the plasma membrane detach from it; the nucleus shows an irregular outline and aberrations in the nucleolus and chromosomes; the chloroplasts decompose the internal structures and, in a number of cells, transform into proplastid-like organelles. Also, the development of the proplastid into chloroplast in etiolated algae exposed to the light in the presence of DMSO is highly disturbed.These results show that DMSO has remarkable side effects like all the cytoskeletal poisons experimented up to now. An interpretation of the nuclear and chloroplast alterations is advanced.

Analisi ultrastrutturale degli effetti della monensina in Euglena gracilis, con particolare riguardo all'apparato di Golgi

Abstract Ultrastructural analysis of the effects of monensin in Euglena gracilis, with special reference to the Golgi apparatus. - The monovalent ionophore, monensin, is known to affect the mature (trans) half of the dictyosomes of several organisms, including Euglena gracilis. We demonstrated that the exposure to high concentrations of this compound (2.5 × 10−5 to 10−4M) provoked remarkable swelling also in the forming (cis) half of Euglena cisternae. Additional dilations affected the thylakoids of both mature chloroplasts and proplastids of greening cells in which the organelle development was slower than in the control group. No osmotic swelling was observed for the mitochondria. Since monnesin exchanges one proton for each monovalent cation (Na+ or K+) transported, it follows that an energy driven influx of H+ is necessary to accumulate sufficient osmotically active ions in a membrane compartment. Thus it is possible that H+-ATPases are present on both forming and mature half of Euglena dictyosomes.

Ultrastructural Localization of Concanavalin A Binding Sites in Intact Cells of Euglena gracilis

Summary Living cells of Euglena gracilis were exposed to ferritin-coupled concanavalin A and the intracellular distribution of the opaque tracer was examined by electron microscopy. The conjugate entered 15–20% of the organisms and the lectin binding occurred around the chloroplasts and within the chromosomes. A possible relationship between the lectin-chromosome interaction and the mitogenic activity exerted by concanavalin A on Euglena cells is discussed.