Wall morphogenesis in diatoms: Deposition of silica by cytoplasmic vesicles

Summary Several TEM and SEM techniques were applied to examine developing structures in valves of the centric diatomThalassiosira eccentrica (Ehrenb.) Cleve after cytokinesis. It was possible to confirm that in each stage of the silicification process there is a distinction between a growing zone with a loose assemblage of silica spheres and a compacting zone in an older phase of development. The spherical structure of the silica in the growing zone results from the addition of silica by small cytoplasmic vesicles of about 300 to 400 Å in diameter. The vesicle membrane fuses with the silicalemma and the vesicle content is released into the silica-deposition vesicle. The origin of these vesicles, named STV, is still unknown.     

Quantum-mechanical kinetic study of the primary reaction of the photochemical cycle of Halobacterium halobium

A two-frequency oscillator model for the primary photochemical reaction bacteriorhodopsin batho-bacteriorhodopsin (K₆₁₀) is proposed. According to this model two conformational changes in the reaction are considered to take place: the first one is a distortion of the retinal in the bacteriorhodopsin active site and the second one is a conformational transition of the bacterioopsin, affecting the native structure hydrogen bonds. On the basis of this model the temperature dependences of the rate constants for normal and deuterated reactants are calculated in good agreement with the available experimental data. The relations of the reaction considered to the primary photochemical reaction of vision are discussed.     

An alkali-soluble polysaccharide from the cell walls of Coprinus lagopus

An alkali-soluble polysaccharide was isolated from the purified mycelial walls of Coprinus lagopus. The hydrolysis products, optical rotation, and infrared spectrum indicate a -glucan. Hydrolysis of the glucan after permethylation gave only 2,3,4,6-tetra-, 2,4,6-tri-, and 2,4-di-O-methyl-d-glucose. These methylated sugars and their relative quantities reveal that the glucan is a polysaccharide containing -1,3-linked glucose units with about 14% of the sugars having 1,6-linked branch points. Partial hydrolysis of the product derived from Smith degradation of the glucan released laminaribiose and gentiobiose suggesting that the branches are generally longer than a single glucose unit.Adapted from a portion of a dissertation submitted in partial fullfillment of the requirements for the Ph.D. degree in botany at the University of Connecticut under the direction of Dr. Ralph P. Collins     

Polysaccharide and oligosaccharide changes in germinating lupin cotyledons

In germinating lupin cotyledons, there was a rapid depletion of raffinose series oligosaccharides, a temporary increase in sucrose and constant low levels of reducing monosaccharides. The major polysaccharide fraction was extracted with hot NH₄ oxalate—EDTA solution and had the constitution of intercellular/cell wall polysaccharide. GLC examination of component sugars showed that as cotyledons expanded this fraction was depleted and that there was selective hydrolysis of arabinose and galactose, so that the uronic acid proportion increased. Gel and DEAE-cellulose chromatography showed that this fraction became more heterogeneous. The neutral and acidic fractions were separated and the component sugars, viscosities, gel chromatographic behaviour and sedimentation constants of these determined. The results indicated that in the later phase of plant cell wall expansion in germinating lupin cotyledons the arabinogalactan side chains of the pectic polysaccharide fraction are selectively hydrolysed leaving a primary wall with a high uronic acid content.     

The change of pattern in microfibril arrangement on the inner surface of the cell wall of Closterium acerosum during cell growth

Closterium acerosum (Schrank) Ehrenberg cells cultured on cycles of 16 h light and 8 h dark, undergo cell division synchronously in the dark period. After cell division, the symmetry of the daughter semicells is restored by controlled expansion, the time required for this restoration, 3.5–4 h, being relatively constant. The restoration of the symmetry is achieved by highly oriented surface expansion occurring along the entire length of the new semicell. During early semicell expansion, for about 2.5 h, microfibrils are deposited parallel to one another and transversely to the cell axis on the inner surface of the new wall. Wall microtubules running parallel to the transversely oriented microfibrils are observed during this period. About 2.5 h after septum formation, preceding the cessation of cell elongation, bundles of 7–11 microfibrils running in various directions begin to overlay the parallel-arranged microfibrils already deposited. In the fully elongated cells, no wall microtubules are observed.     

Cell wall regeneration by protoplasts of Chlamydomonas

Protoplasts from Chlamydomonas smithii prepared by the action of C. reinhardii gamete autolysine have been studied with respect to cell wall regeneration. Natural protoplasts within sporangia were also investigated for purposes of comparison. In both cases a new cell wall is completed within 2–3 h of the onset of regeneration. The first visible stages of wall regeneration are to be seen after 40–60 min as a fine fringe outside of the plasmalemma. The development of the typical central triplet follows within the next 1 h. Cell wall regeneration is reversibly inhibited by cycloheximide (10g ml^-1) and reversibly disturbed by concanavalin A (50 g ml^-1). Actinomycin D at concentration over 100g ml^-1 also inhibit but the inhibition is irreversible and peculiar membrane effects are observed. Chelators (ethylenediamine tetraacetic acid; ethyleneglycol-bis-aminoethyl ether) and 2-deoxyglucose slightly retard or have no effect on cell wall regeneration.Abbreviations EDTA ethylenediamine tetraacetic acid - EGTA ethyleneglycol-bis(aminoethyl ether) - N,N tetraacetic acid     

Chemical inhibition of cell wall formation and cytokinesis,but not of nuclear division,in protoplasts of Nicotiana tabacum L. cultivated in vitro

The effect of cytochalasin B, colchicine, coumarin and 2,6-dichlorobenzonitrile on cell wall formation and cellular division was studied by light and electron microscopy with tobacco mesophyll protoplasts cultivated in vitro. 2,6-dichlorobenzonitrile was found to be the most effective and reversible inhibitor of cell wall formation. The other inhibitors caused irreversible damage and/or inhibited mitosis. In protoplasts cultivated in the presence of 2,6-dichlorobenzonitrile the total inhibition of cell wall formation had no effect on nuclear division, but cytokinesis was totally inhibited so that multinucleate protoplasts were obtained.Abbreviations DB 2,6-dichlorobenzonitrile=dichlobenil - CB cytochalasin B     

Isolation and characterization of an extracellular hydroxyproline-rich glycoprotein and a mannose-rich polysaccharide from Eudorina californica (Shaw)

Mucilage and colony walls of E. californica were separated from the cells by homogenization, filtration, and differential centrifugation. The chief components of the mucilage were a high-molecular-weight (MW) hydroxyproline-rich glycoprotein and a very high-MW polysaccharide in the proportions 47% and 34%, respectively. The glycoprotein consisted of galactose, arabinose, xylose and an unidentified neutral sugar; and the amino acids cysteine, aspartic acid, glutamic acid, arginine, lysine, glycine, serine, methionine, histidine, alanine, proline, hydroxyproline, tyrosine, threonine, valine, phenylalanine, isoleucine and leucine. The principal sugar of the polysaccharide was mannose. The chemical composition of the colony walls was essentially the same as that of the glycoprotein in the mucilage except that there was almost twice as much hydroxyproline. Also the protein content of the colony walls was 34% while that of the glycoprotein in the mucilage was 22%. No glucose, sugar acids or nucleic acids were found in the extracellular matrix.     

Effect of papulacandin B on β-glucan synthesis in Schizosaccharomyces pombe

Abstract The antifungal antibiotic papulacandin β inhibited B(1,3)glucan-synthase activity, in vitro, from Schizosaccharomyces pombe . Levels of β(1,3)glucan-synthase from antibiotic-treated cultures were lower than the control cultures whereas mannan-synthase and β(1,3)glucanase activities were almost unaffected. The presence of an osmotic stabilizer reduced the inhibition of growth caused by the antibiotic. Addition of papulacandin β to a culture of S. pombe specifically inhibited incorporation of glucose into the β-glucan cell wall fraction. The fatty acids as well as the hydroxyl groups on the phenol residue of the papulacandin β molecule were essential for the inhibitory activity.     

Possible role of cell cycle-dependent morphology,geometry, and mechanical properties in tumor cell metastasis

Studies that examine the shear- and abrasion-sensitivity of proliferating cells are important in order to understand the behavior of hybridoma cells in bioreactor culture and metastasizing cancer cells in the bloodstream. Little is known about the link between morphology, structure, and mechanical properties of a given cell line, especially with respect to variations throughout the cell cycle. In our experiments with GAP A3 hybridoma cells, distinct cell morphologies were identified and correlated with phases of the cell cycle by video microscopic observation of synchronized cells, and of individual cells that were followed throughout their cell cycle. Micropipet manipulation was used to measure the geometrical (cell volume) and mechanical (apparent cell viscosity) properties of single cells. As the cell cycle progressed at 37°C, an increase in cell volume from 1400 μm³ to 5700 μm³ was accompanied by an increase in apparent cell viscosity from 430 poise to 12,000 poise, consistent with an accumulation of more cytoplasmic material in the “older” cells. Hybridomas are representative of the various leukemias derived from hemopoietic cells, and even though as a whole, they appeared to be rather shear-insensitive, the wide range of property values demonstrates that a given cell line cannot be characterized by a single value for any one property, and that properties must be related to the cell cycle when considering proliferating cells. It is interesting to see if distinct stages in the metastatic sequence of events might correlate with any of these physical features of the cell cycle, irrespective of cell type or cell line. For example, the cytokinetic doublet could represent a fragile structure that may fail and produce cell death under fluid-shear conditions that would not affect the cells at any other stage in the cell cycle. Identifying such cell cycle-dependent features in metastasizing cancer cells could lead to a better understanding of the metastatic process and to possible clinical treatments directed at making cells more shear- and abrasion-sensitive, and therefore, more likely to be killed by the natural hydrodynamic forces of the circulatory system.