Layer Cell Wall Research Articles

S-layer and cytoplasmic membrane - exceptions from the typical archaeal cell wall with a focus on double membranes.

The common idea of typical cell wall architecture in archaea consists of a pseudo-crystalline proteinaceous surface layer (S-layer), situated upon the cytoplasmic membrane. This is true for the majority of described archaea, hitherto. Within the crenarchaea, the S-layer often represents the only cell wall component, but there are various exceptions from this wall architecture. Beside (glycosylated) S-layers in (hyper)thermophilic cren- and euryarchaea as well as halophilic archaea, one can find a great variety of other cell wall structures like proteoglycan-like S-layers (Halobacteria), glutaminylglycan (Natronococci), methanochondroitin (Methanosarcina) or double layered cell walls with pseudomurein (Methanothermus and Methanopyrus). The presence of an outermost cellular membrane in the crenarchaeal species Ignicoccus hospitalis already gave indications for an outer membrane similar to Gram-negative bacteria. Although there is just limited data concerning their biochemistry and ultrastructure, recent studies on the euryarchaeal methanogen Methanomassiliicoccus luminyensis, cells of the ARMAN group, and the SM1 euryarchaeon delivered further examples for this exceptional cell envelope type consisting of two membranes.

Experimental and numerical study on the mechanical response of Nomex honeycomb core under transverse loading

This paper presents an experimental and numerical investigation on the mechanical response of the Nomex honeycomb core subjected to transverse loading. Here, a series of tensile, stabilized compressive and step-by-step compressive tests were carried out, also a meso-scale finite element modelling method was developed to simulate the resin-paper-resin layered honeycomb cell walls by employing explicit shell elements. Through the analysis of the test results, the brittle fracture behaviour of the phenolic resin coating is recognised as a main reason of the honeycomb collapse. Both the strength and modulus of the honeycomb core in tension are higher than those in compression, due to the local buckling of the thin cell walls at a quite low level of compressive loading. From the numerical analysis, it was found that the volume of the resin coating has a positive effect on the collapse strength of the honeycomb core, however has no influence on the collapse strain. Moreover, the modulus of the resin coating has a positive effect on the collapse strength but a negative effect on the collapse strain. In addition, the strength of the resin coating has positive effects on both the collapse strength and strain of the honeycomb core.

A novel mutant gene for (1-3, 1-4)-.BETA.-D-glucanless grain on barley (Hordeum vulgare L.) chromosome 7H

(1-3, 1-4)-β-D-glucan contained in barley (Hordeum vulgare L.) grains is a main component of endosperm cell walls and constitutes the cell wall matrix with arabinoxylan. A monofactorial recessive mutant gene for (1-3, 1-4)-β-D-glucanless grain was found and the new gene was designated as bgl (= (1-3, 1-4)-beta-D-glucanless grain). A linkage was found between the bgl gene and the naked caryopsis (nud) gene, and it was mapped to the centromeric region of chromosome 7H. Phenotypes in bgl cosegregated with the polymorphisms in HvCslF6, a member of cellulose synthase-like HvCslF gene family, indicating that bgl was caused by a mutation in the HvCslF6 locus. In order to clarify the characteristics of (1-3, 1-4)-β-D-glucanless barley grains, a near-isogenic line (NIL) was developed by backcrossing the Japanese two-rowed cultivar ‘Nishinohoshi’ as a recurrent parent. The NIL with bgl completely lacked (1-3, 1-4)-β-D-glucan in both the endosperm and aleurone layer cell walls. Microscopic analysis revealed that the NIL had thin endosperm cell walls. It also showed a softer grain texture and many more broken grains during the pearling process than the recurrent parent. The soft and friable grain texture of the NIL was probably caused by the thin endosperm cell walls.

Anatomical and biochemical changes in the composition of developing seed coats of annatto (Bixa orellana L.)

Seeds of Bixa orellana (L.) have a sclerified palisade cell layer, which constitutes a natural barrier to water uptake. In fact, newly fully developed B. orellana seeds are highly impermeable to water and thereby dormant. The purpose of this work is to investigate, from a developmental point of view, the histochemical and physical changes in the cell walls of the seed coat that are associated with the water impermeability. Seed coat samples were analyzed by histochemical and polarization microscopy techniques, as well as by fractionation/HPAEC-PAD. For histochemical analysis the tissue samples were fixed, dehydrated, embedded in paraffin and the slides were dewaxed and tested with appropriate stains for different cell wall components. Throughout the development of B. orellana seeds, there was a gradual thickening of the seed coat at the palisade region. This thickening was due to the deposition of cellulose and hemicelluloses in the palisade layer cell walls, which resulted in a highly water impermeable seed coat. The carbohydrate composition of the cell walls changed dramatically at the late developmental stages due to the intense deposition of hemicelluloses. Hemicelluloses were mainly deposited in the outer region of the palisade layer cell walls and altered the birefringent pattern of the walls. Xylans were by far the most abundant hemicellulosic component of the cell walls. Deposition of cellulose and hemicelluloses, especially xylans, could be responsible for the impermeability to water observed in fully developed B. orellana seeds.

Drought Stress Effects on Root Anatomical Characteristics of Rice Cultivars (Oryza sativa L.)

The objective of this study was to compare some aspects of root anatomy of rice cultivars under irrigation and submerged conditions. Seedling of three new rice cultivars (Zayande-Rood, 829 and 216) were transferred to 9 lysiometers (200 x 120 x 100 cm) according to a randomized block design with two treatments (submerged and aerated condition) in three replicates. The amount of water consumption was recorded during growing season. Cross-sections of plant roots were obtained at two different times; two and four months after seedling. The root samples were prepared from 20 mm of tip. Root cross-sections were successively stained with 1% aqueous solutions of Methyl green and Congo red. Figures of sections were made by LM. Anatomical differences were observed among the three cultivars submitted to water regimes regarding the amount of aerenchyma tissue and cell walls of secondary tissues. The irrigated roots of the three cultivars presented a decreasing tendency in the proportion of the area of the cortex destined for the aerenchyma besides thickening of the cell walls of endodermis, pith and sclerenchyma layer cells. The rate of aerenchyma disappearing in the irrigated plants suggested different behaviors in different cultivars. Zyande-Rood and 829 cultivars exhibited extensive aerenchyma disappearing when the plants was irrigated compared to others. The sclerenchyma layer cell walls in 2-month-old roots were higher in irrigated plants and also was higher in Zayande-Rood cultivar. The result of xylem vessels wall indicated that the thicknesses of xylem vessels under submerged and irrigated condition were 3.6 and 7.9 mu in Zyande-Rood cultivar respectively. The thicknesses of endoderm cell wall of the submerged roots ranged from 4.6 to 10.8 mu for Zyande-Rood cultivar in submerged and irrigated conditions respectively and were lower for other cultivars. The water consumptions were 43.04 and 82.5 cm in whole season for irrigated and submerged condition, respectively.

Effects of calcium chloride treatments on wheat grain peroxidase activity and outer layer mechanical properties

AbstractWheat grain soaking in calcium solutions was used as a tool to enhance endogenous peroxidase activities and follow potential changes in outer layer mechanical properties and cell wall phenolic profile. Treatment with 10 mmol L−1 calcium chloride was found to increase peroxidase activities in grains from two cultivars differing in kernel hardness, but at a different level. Concomitantly, mechanical properties of the outer layers from treated grains, assessed by uniaxial tension tests, showed significant stiffening depending on wheat cultivar. These changes were also observed in tissues after removal of the outer pericarp but not in each of the isolated layers, suggesting that modification of the mechanical properties occurs at the interface between the aleurone layer and the surrounding tissues. Analyses of the outer layer phenolic acid composition after mild or severe alkaline hydrolysis and of released lignin monomers after thioacidolysis appeared in accordance with the observed changes in tissue mechanical properties and suggest modification of cell wall compound interactions. Copyright © 2006 Society of Chemical Industry

Effect of wheat bran ball-milling on fragmentation and marker extractability of the aleurone layer

Bran (branml) obtained by roller milling of soft (Scipion) and hard (Baroudeur) wheat cultivars was further ball-milled for increasing times and the observed particle size distribution expressed as a dispersion index. Bran (branhi) and aleurone layers were also hand-isolated from the same grains and the pattern of size reduction during ball-milling were compared with branml. Branml and branhi were found to fracture more rapidly than isolated aleurone layers due to the presence of the highly friable pericarp and the possible mechanical constraints due to tissues surrounding the aleurone layer. Previously identified markers of the aleurone layer cell contents (phytates) and cell walls (p-coumaric acid) were used to determine their water extractabilities from ball-milled samples and the state and degree of dissociation of the aleurone layer, either as an isolated tissue or within branml and branhi. The results suggest that ball-milling rapidly induces fractures in walls of cells in the aleurone layer. The partial opening of the cells in the aleurone layer allowed extraction of most (≈70%) of the water-extractable phytates, even though their mean particle size was much larger than the dimensions of the cells. A further increase in extractability of phytates was observed when the particle size was reduced below the aleurone cell dimensions. Although much less soluble, p-coumaric acid followed a similar trend to phytates. The different behaviour of branml and branhi was consistent with a weakening effect of the tissues in the former, probably due to the previous milling process. The bran and aleurone layers from both wheat varieties exhibited a similar behaviour.

Structural Research on Surface Layers: A Focus on Stability, Surface Layer Homology Domains, and Surface Layer–Cell Wall Interactions

Surface layers (S-layers) fromBacteriaandArchaeaare built from protein molecules arrayed in a two-dimensional lattice, forming the outermost cell wall layer in many prokaryotes. In almost half a century of S-layer research a wealth of structural, biochemical, and genetic data have accumulated, but it has not been possible to correlate sequence data with the tertiary structure of S-layer proteins to date. In this paper, some highlights of structural aspects of archaeal and bacterial S-layers that allow us to draw some conclusions on molecular properties are reviewed. We focus on the structural requirements for the extraordinary stability of many S-layer proteins, the structural and functional aspects of the S-layer homology domain found in S-layers, extracellular enzymes and related functional proteins, and outer membrane proteins, and the molecular interactions of S-layer proteins with other cell wall components. Finally, the perspectives and requirements for structural research on S-layers, which indicate that the investigation of isolated protein domains will be a prerequisite for solving S-layer structures at atomic resolution, are discussed.

Isolation and fractionation of cell envelope from the extreme thermo-acidophile Sulfolobus acidocaldarius

Methods to produce membrane fragment of defined composition were evaluated for their applicability to the extremely thermophilic, acidophilic archaeon Sulfolobus acidocaldarius. Sonication was found to effectively disrupt Sulfolobus cells and to produce small vesicles of varying size. Alternatively, grinding cells with fine alumina yielded large, uniform vesicles retaining the characteristic cell envelope ultrastructure of Sulfolobus spp. Biochemical and electron-microscopic examination indicated that the ‘cell ghosts’ prepared from S. acidocaldarius by the latter method have a relatively simple protein composition dominated by the glycoprotein subunits of the organism's quasicrystalline surface (S) layer cell wall. By suitable treatments, the cell ghosts could, in turn, be used to prepare S layer without the associated lipid membrane, or conversely, to prepare cytoplasmic membrane lacking the apposed S layer. These results offer a basis for compositional and functional analyses of a cell surface that is normally exposed to extremely severe environmental conditions.

Fine structure of the phylogenetically important marine algaRhodogorgon carriebowensis (Rhodophyta, Batrachospermales?)

The fine structure of the recently described red algaRhodogorgon carriebowensis J. Norris et Bucher was studied by light microscopy and scanning and transmission electron microscopy to aid in the ordinal placement of this unusual alga. Most significant in this context were findings that pit plugs had two-layered plug caps, the outer layer of which formed a large dome and was composed of glycoprotein. Cap membranes appeared to be absent. Medullary cells were remarkable in having extremely thick, layered cell walls, whose inward deposition left little room for cytoplasm. Medullary filaments branched little except near the base of the cortex. The assimilatory filaments that made up most of the cortex contained almost all the pigmentation and starch reserves of the thallus. These filaments terminated in either slender apical cells with smooth cell walls or bulbous apical cells bearing spinulose projections. Two types of elongated cells were found in the cortex, those with calcified cell walls and those surrounded by multiple, spreading layers of wall material. Neither cell type was pigmented. The latter type sometimes supported normal assimilatory cells.

The effect of aculeacin A and papulacandin B on morphology and cell wall ultrastructure in Candida albicans.

Transmission (TEM) and scanning electron microscopy (SEM) of Candida albicans cultures treated with the cell wall active antibiotics aculeacin A and papulacandin B (10 micrograms/mL) revealed highly distorted, wrinkled, and collapsed cells. Dividing cells failed to separate properly and aggregates of enlarged and elongated forms were often seen. TEM sections revealed thick and layered cell walls in the treated cultures and bud cross walls failed to segregate completely. Approximately 20% of the cells demonstrated complete cell necrosis accompanied with cytoplasmic deterioration, layered and distorted walls, and improperly formed buds and scars.

Use of tannic acid as a fixative-mordant to improve the ultrastructural appearance ofCandida albicansblastospores

Blastospores of Candida albicans, grown in YM broth (Difco, pH 6.0), were treated with tannic acid as part of a fixation schedule with glutaraldehyde and osmium tetroxide. The results obtained were compared to routine fixation procedures employing glutaraldehyde-osmium tetroxide and potassium permanganate, as well as several schedules using various combinations of the aforementioned fixatives. Glutaraldehyde-osmium tetroxide-tannic acid fixed cells had several morphological structures accentuated, including sharply delineated cytoplasmic and organelle membranes, a detailed cytoplasmic matrix, and an intensified layered cell wall. Tannic acid has been found to react as a mordant between osmium tetroxide and lead citrate, forming a "stabilizing matrix" within the cells. Blastospores appeared to have an improved comprehensive ultrastructural appearance, a result of the tannic acid-matrix preserving cellular components for electron microscopy.

Fine structure of cellulose microfibrils in poplar gelatinous layer and Valonia

Fine structure of cellulose microfibrils in poplar (Populus euramericana) gelatious layer and Valonia cell walls was observed in the electron microscope by using disintegration and ultrathin section techniques with various electron stains. Staining of the gelatinous layer in poplar showed that the microfibrils had a paracrystalline region surrounding a crystalline core, but such a region was negligible in Valonia. From the facts that kinks and shortened microfibrils were observed after mechanical and hydrolysis treatments, respectively, and that the microfibrils were unaffected by negative staining, it was concluded that the microfibril core is uniformly crystalline in the longitudinal direction although there may be some crystalline dislocations.

Electron Microscopy of Young Candida albicans Chlamydospores

One- to three-day-old cultures of Candida albicans bearing chlamydospores were grown and harvested by a special technique, free of agar, and prepared for ultramicrotomy and electron microscopy. These young chlamydospores exhibited a subcellular structure similar to that of the yeast phase, e.g., cytoplasmic membrane, ribosomes, and mitochondria. Other structural characteristics unique to chlamydospores were a very thick, layered cell wall, the outer layer of which was continuous with the outer layer of the suspensor cell wall and was covered by hair-like projections; membrane bound organelles; and large lipoid inclusions. Only young chlamydospores less than 3 to 4 days old exhibited these ultrastructural characteristics.

Biochemical localization of alkaline phosphatase in the cell wall of a marine pseudomonad.

The various layers of the cell envelope of marine pseudomonad B-16 (ATCC 19855) have been separated from the cells and assayed directly for alkaline phosphatase activity under conditions established previously to be optimum for maintenance of the activity of the enzyme. Under conditions known to lead to the release of the contents of the periplasmic space from the cells, over 90% of the alkaline phosphatase was released into the medium. Neither the loosely bound outer layer nor the outer double-track layer (cell wall membrane) showed significant activity. A small amount of the alkaline phosphatase activity of the cells remained associated with the mureinoplasts when the outer layers of the cell wall were removed. Upon treatment of the mureinoplasts with lysozyme, some alkaline phosphatase was released into the medium and some remained with the protoplasts formed. Cells washed and suspended in 0.5 M NaCl were lysed by treatment with 2% toluene, and 95% of the alkaline phosphatase in the cells was released into the medium. Cells washed and suspended in complete salts solution (0.3 M NaCl, 0.05 M MgSO(4), and 0.01 M KCl) or 0.05 M MgSO(4) appeared intact after treatment with toluene but lost 50 and 10%, respectively, of their alkaline phosphatase. The results suggest that the presence of Mg(2+) in the cell wall is necessary to prevent disruption of the cells by toluene and may also be required to prevent the release of alkaline phosphatase by toluene when disruption of the cells by toluene does not take place.

Ultrastructure of Actinomyces viscosus and Actinomyces naeslundii

Electron micrographs of freeze-etched, thin-sectioned, shadowed and negatively-stained cells were presented. Fibril-like structures were observed on the outer surface of both organisms in all preparations. Thin sections revealed a layered cell wall in both microbes, but the layering was particularly distinct in A. naeslundii. Freeze-etching of both species demonstrated two layers in the cytoplasmic membrane. The outermost layer of the plasma membrane was shown to have numerous particles, while the second layer had a smooth surface with evenly dispersed dome-like structures. Since plaque organisms have many of the structures described here, they may be members of the genus Actinomyces. The demonstration of fibres on the outer surface of these bacteria provides structural evidence for a potential mechanism of adhesion. These observations are of special interest as both organisms induce experimental periodontal disease in hamsters and gnotobiotic rats.

Hyphal structure in Fusarium oxysporum (Schlecht) revealed by freeze-etching.

Freeze-etched hyphae of F. oxysporum exhibited a single layered cell wall; a plasmalemma, in which invaginations were frequently associated with paramural vesicles; cytoplasma bearing lipid droplets, vacuoles, intravacuolar vesicles and nuclei with typical nuclear pores. Some hyphae bore crystalline inclusions characterized by a pronounced hexagonal, external ornamentation and it is suggested that the presence of these crystals and intravacuolar vesicles are indicative of aging hyphae.

Morphology and chemistry of the bacterial cell wall. 1. The location of mucopeptide in the cell wall of Bacteroides convexus and its chemical composition.

The location of the mucopeptide in the cell wall of Bacteroides convexus was determined by electron microscope after enzymatic and chemical treatment (papain, pepsin, lysozyme and phenol). In the five layered cell wall the innermost electron dense layer (or a part of it) proved to be the mucopeptide. The molar ratio of amino sugar and amino acid components of purified mucopeptide was about 1:1:1:1:1:1 for glucosamine, muramic acid, L-alanine, D-glutamic acid, DL(meso)-diaminopimelic acid and D-alanine.