Composition of the sheath produced by the green alga Chlorella sorokiniana

AIMS: To investigate the chemical characterization of the mucilage sheath produced by Chlorella sorokiniana. METHODS AND RESULTS: Algal mucilage sheath was hydrolysed with NaOH, containing EDTA. The purity of the hydrolysed sheath was determined by an ATP assay. The composition of polysaccharide in the sheath was investigated by high-performance anion-exchange chromatography with pulsed amperometric detection. Sucrose, galacturonic acid, xylitol, inositol, ribose, mannose, arabinose, galactose, rhamnose and fructose were detected in the sheath as sugar components. Magnesium was detected in the sheath as a divalent cation using inductively coupled argon plasma. The sheath matrix also contained protein. CONCLUSIONS: It appears that the sheath is composed of sugars and metals. Mucilage sheath contains many kinds of saccharides that are produced as photosynthetic metabolites and divalent cations that are contained in the culture medium. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report on chemical characterization of the sheath matrix produced by C. sorokiniana.     

Monoclonal antibody characterisation of slime sheath: the extracellular matrix of Dictyostelium discoideum

Proteins can be extracted from the slime sheath of Dictyostelium discoideum slugs by denaturing agents. A subset of these proteins is also released by cellulase digestion of the sheath, implying that protein-protein and protein-cellulose interactions are involved in sheath protein retention. It seems probable that the cellulose-associated sheath proteins are also associated with the cellulose of mature stalk cells. Monoclonal antibodies directed against sheath demonstrate extensive sharing of antigenic determinants between sheath proteins and a limited degree of antigenic sharing between sheath and slug cell proteins. All of the proteins recognised by these monoclonal antibodies are developmentally regulated. These results are discussed in terms of the structure of the sheath and its possible role(s) in D. discoideum development.     

Characterization of novel, phenol-soluble polypeptides which confer rigidity to the sheath of Methanospirillum hungatei GP1.

Treatment of the Methanospirillum hungatei GP1 sheath with 90% (wt/vol) phenol resulted in the solubilization of a novel phenol-soluble group of polypeptides. These polypeptides were purified by the removal of insoluble material by ultracentrifugation and represented approximately 19% of the mass of the sheath. The phenol-insoluble material resembled untreated sheath but had lost its rigidity and cylindrical form. Recombination of phenol-soluble and phenol-insoluble fractions by dialysis to remove phenol resulted in cylindrical reassembly products. Although bona fide sheath (complete with the 2.8-nm lattice) was not produced, a role for the phenol-soluble polypeptides in the maintenance of sheath rigidity is implied. The phenol-soluble polypeptides have limited surface exposure as detected by antibodies on intact sheath; therefore, they are not responsible for the 2.8-nm repeat occurring on the outer face of the sheath. However, longitudinal and transverse linear labeling by protein A-colloidal gold on the outer and inner faces, respectively, occurred with monoclonal antibodies specific to the phenol-soluble polypeptides. Restricted surface exposure of phenol-soluble polypeptides on the sheath highlighted molecular defects in sheath architecture. These lattice faults may indicate sites of sheath growth to accommodate cell growth or division (longitudinal immunogold label) and filament division (transverse immunogold label). The identification of a second group of polypeptides within the infrastructure of the sheath suggests that the sheath is a trilaminar structure in which phenol-soluble polypeptides are sandwiched between sodium dodecyl sulfate-beta-mercaptoethanol-EDTA-soluble polypeptides (G. Southam and T. J. Beveridge, J. Bacteriol. 173:6213-6222, 1991) (phenol-insoluble material).     

Structural analysis of the fundamental polymer of the sheath constructed by Sphaerotilus natans

The sheath of Sphaerotilus natans is composed of cysteine-rich peptide and polysaccharide moieties. The polysaccharide was prepared by treating the sheath with hydrazine, and was determined to be a mucopolysaccharide containing beta-D-GlcA, beta-D-Glc, alpha-D-GalN, and beta-D-GalN. To elucidate the structure of the peptide, the sheath was labeled with a thiol-selective fluorogenic reagent, 4-(aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole. Enantiomeric determination of the S-derivatized Cys in the fluorescent sheath suggested that it contained L-Cys mainly. Fluorescent cysteinylglycine was detected in the partial acid hydrolysate of the fluorescent sheath. The sheath-degrading enzyme secreted by Paenibacillus koleovorans produced a fluorescent disaccharide-dipeptide composed of GalN, Gly, and N-acetylated Cys from the fluorescent sheath. The disaccharide and dipeptide moieties were found to be connected by an amide bond. Based on these results, the sheath was deduced to be formed by association of a mucopolysaccharide modified with N-acetyl-L-cysteinylglycine.     

Isolation and characterization of a component of the surface sheath of Dictyostelium discoideum

Aggregates of Dictyostelium discoideum are surrounded by a surface sheath which functions to maintain polarity and integrity during development. We have isolated and partially characterized a component of the surface sheath. It is composed of 60% cellulose, 15% protein, 3% heteropolysaccharide (heteropolymer), 5% lipid, and 1% sulfate when isolated from migrating slugs. The sheath, isolated from aggregates prior to tip formation, has less protein, a different heteropolymer, and cellulose of a lower crystallinity than the sheath of migrating slugs. The increase in crystallinity of the cellulose during development may be important in determining the strength of the surface sheath.     

Fine structure of the abdominal neural fat-body sheath in the stick insect (Carausius morosus,Br.)

The neural fat-body sheath surrounding the abdominal ventral nerve cord of Carausius morosus has been examined by light and electron microscopy. A perineural chamber between the ventral nerve cord and the sheath is present in the ganglionic regions, but in the interconnective regions the sheath directly covers the neural lamella. The sheath is differentiated into secretory cells with abundant granular endoplasmic reticulum and many mitochondria and storage cells with lipid droplets and granules presumed to be glycogen. The whole sheath is pervaded with tracheoblast cells and associated tracheal and tracheolar tubules. Recent evidence suggests that this sheath may have little power of ionic regulation. The function of the sheath, deduced from the fine structure described here, appears to be to serve the nutritional needs of the central nervous system. Why a sheath of this type appears to be confined to herbivorous insects with unusual haemolymph cationic balance is still unexplained.     

The structure of the cuticle and sheath of the infective juvenile of Trichostrongylus colubriformis

The infective third-stage juvenile of Trichostrongylus colubriformis is surrounded by its own cuticle as well as the incompletely moulted cuticle of the second-stage juvenile, which is referred to as the sheath. The sheath comprises an outer epicuticle, an amorphous cortical zone, a fibrous basal zone and an inner electron-dense layer. The basal zone of the sheath consists of three layers of fibres; the fibres are parallel within each layer, but the fibre direction of the middle layer is at an angle to that of the inner and outer layers. The cuticle comprises a complex outer epicuticle, an amorphous cortical zone and a striated basal zone. The lateral alae of the cuticle and the sheath are aligned and overlie the lateral hypodermal cords. The lateral alae of the sheath consist of two wing-like expansions of the cortical zone with associated specializations of the inner electron-dense layer which form a groove. The cuticular lateral alae consist of two tube-like expansions of the cortical zone. The lateral alar complex of the cuticle and the sheath may maximise locomotory efficiency and prevent rotation of the juvenile within the sheath.     

The distribution of nucleic acids in the giant axon of the squid (Loligo pealii)

Abstract— RNA and DNA were determined in the axoplasm and sheath of squid giant axons. If the RNA was related to axonal length, equivalent amounts of RNA were found in the axoplasm and sheath. However, when it was expressed as a function of dry wt. or residue protein, the concentration of RNA in the sheath was four times greater than in the axoplasm. A ratio of 1·1 was found for sheath RNA/sheath DNA. Less DNA was present in the axoplasm than the amount which could be accurately determined with the methods employed.     

Patterns of sheath elongation, cell proliferation, and manganese(II) oxidation in Leptothrix cholodnii

Leptothrix cholodnii is a Mn(II)-oxidizing and sheath-forming member of the class β-Proteobacteria. Its sheath is a microtube-like filament that contains a chain of cells. From a chemical perspective, the sheath can be described as a supermolecule composed of a cysteine-rich polymeric glycoconjugate, called thiopeptidoglycan. However, the mechanism that controls the increase in sheath length is unknown. In this study, we attempted to detect sheath elongation through microscopic examination by using conventional reagents. Selective fluorescent labeling of preexisting or newly formed regions of the sheath was accomplished using combinations of biotin-conjugated maleimide, propionate-conjugated maleimide, and a fluorescent antibiotin antibody. Epifluorescence microscopy indicated that the sheath elongates at the terminal regions. On the bases of this observation, we assumed that the newly secreted thiopeptidoglycan molecules are integrated into the preexisting sheath at its terminal ends. Successive phase-contrast microscopy revealed that all cells proliferate at nearly the same rate regardless of their positions within the sheath. Mn(II) oxidation in microcultures was also examined with respect to cultivation time. Results suggested that the deposition of Mn oxides is notable in the aged regions. The combined data reveal the spatiotemporal relationships among sheath elongation, cell proliferation, and Mn oxide deposition in L. cholodnii.     

Analysis of the Transition Time between the Space-Charge-Limited and Inverse Regimes

Plasma Physics Reports - Accumulation of cold ions trapped within a space-charge-limited sheath collapses the sheath, causing a transition to the inverse sheath mode. A driving mechanism creating...     

玉米自交系K10白色叶鞘遗传机理研究

玉米白色叶鞘是重要的遗传研究材料。本研究以玉米白色叶鞘自交系K10为研究材料,对白色叶鞘性状进行了遗传机理初探和基因初步定位。以白色叶鞘自交系K10与多个自交系进行正反交,F1均表现为绿色叶鞘,表明该白色叶鞘性状与细胞质遗传无关,由隐性核基因控制。而F2分离比例均不符合孟德尔遗传分离定律,证明该性状受多基因控制。在拔节期利用透射电镜对F2分离群体中白色叶鞘和绿色叶鞘植株的叶绿体超微结构观察发现,白色叶鞘细胞中完整的叶绿体结构较少,且大多数没有类囊体片层及基粒。绿色叶鞘植株和白鞘植株叶片中叶绿素a、叶绿素b以及总叶绿素含量并不存在显著差异,而K10白色叶鞘中三者含量均低于正常植株叶鞘。利用SSR分子标记技术对白色叶鞘性状进行初步定位,共定位到2个基因位点,分别位于第8(qws8)和第9(qws9)染色体。     

Some characteristics of cyclic photophosphorylation in maize bundle sheath chloroplasts

PMS-dependent photophosphorylation in bundle sheath chloroplasts isolated from Zea mays was monitored by using a continuous method. Carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) and venturicidin were shown to inhibit the ATP-synthesis. Venturicidin has been shown to inhibit ATP-formation in both mesophyll and bundle sheath chloroplasts. In contrast to the case in mesophyll chloroplasts, FMN was not able to promote photophosphorylation in bundle sheath chloroplasts. The effects of other cofactors and inhibitors on the ATP-synthesis in bundle sheath chloroplasts are shown. No photoinduced synthesis of inorganic pyrophosphate was seen, neither in bundle sheath chloroplasts, nor in mesophyll chloroplasts.     

The Partitioning of Photosynthetically Fixed Carbon in the Leaf Blade and Leaf Sheath of Poa pratensis L.

The partitioning of photosynthetically fixed carbon betweencarbohydrate fractions and the processes of export and storagewere compared in mature leaf blades and sheaths of the grassPoa pratensis L. Most of the fixed carbon was destined for exportfrom the leaf blade with only 1% of the carbon fixed duringthe photoperiod being stored after 24 h. Although most of theassimilates imported to the sheath from the blade were subsequentlyexported, there was some unloading and storage of assimilates.Autoradiography was used to compare the translocation of ¹⁴C-labelledassimilates through non-fed areas of leaf blade and sheath andrevealed that the veins in the sheath showed a greater capacityfor storage of assimilates compared to the leaf blade. Biphasickinetics of sucrose and glucose uptake were observed in segmentsof leaf blade and sheath. Although similar carriers for eachof the sugars appear to exist in the blade and sheath, the rateof uptake via these carriers was significantly lower in thesheath compared to the blade. Assuming that unloading proceedsvia a symplastic pathway, it would appear that the conversionof sucrose to starch in the sheath could be an important meansof regulating unloading and in determining sink strength ofthe sheath. It is concluded that although the net amount ofsugars unloaded in the sheath is small, the storage of assimilatesin the vein network could be an important means of bufferingchanges in sucrose concentration in the translocate during periodsof fluctuating assimilation. Key words: Poa pratensis, autoradiography, sugar uptake, leaf blade, leaf sheath     

Structure and distribution of chloroplasts and other organelles in leaves with various rates of photosynthesis

The ultrastructure and distribution of chloroplasts, mitochondria, peroxisomes, and other cellular constituents have been examined in cross sections of leaves from plants with either high or low photosynthetic capacity. Photosynthetic capacity of a given plant cannot be correlated with the presence or absence of grana in bundle sheath cell chloroplasts, the presence or absence of starch grains in bundle sheath or mesophyll cell chloroplasts, the chloroplast size in bundle sheath or mesophyll cells, or the location of chloroplasts within bundle sheath cells. We conclude that the number and concentration of chloroplasts, mitochondria, and peroxisomes in bundle sheath cells is the most reliable anatomical criterion presently available for determining the photosynthetic capacity of a given plant.     

Ultrastructural localization of Mg++- and Ca++-activated adenosine triphosphatase spinal ganglia of the sheep and goat]

Light and electron microscopic investigations on the Mg++- and Ca++-activated ATPase of sheep and goat dorsal root ganglion have been carried out. Reaction products occur in plasma membranes and interfaces between neurons and sheath cells, between adjacent sheath cells and on the surface of unmyelinated fibers. Cytoplasmic protrusions of ganglion cells and numerous surface increasing invaginations of sheath membranes form close connections between neurons and sheath cells.     

The narrow sheath duplicate genes: sectors of dual aneuploidy reveal ancestrally conserved gene functions during maize leaf development

The narrow sheath mutant of maize displays a leaf and plant stature phenotype controlled by the duplicate factor mutations narrow sheath1 and narrow sheath2. Mutant leaves fail to develop a lateral domain that includes the leaf margins. Genetic data are presented to show that the narrow sheath mutations map to duplicated chromosomal regions, reflecting an ancestral duplication of the maize genome. Genetic and cytogenetic evidence indicates that the original mutation at narrow sheath2 is associated with a chromosomal inversion on the long arm of chromosome 4. Meristematic sectors of dual aneuploidy were generated, producing plants genetically mosaic for NARROW SHEATH function. These mosaic plants exhibited characteristic half-plant phenotypes, in which leaves from one side of the plant were of nonmutant morphology and leaves from the opposite side were of narrow sheath mutant phenotype. The data suggest that the narrow sheath duplicate genes may perform ancestrally conserved, redundant functions in the development of a lateral domain in the maize leaf.     

An Enzymic Method for Measuring the Molecular Weight Exclusion Limit of Plasmodesmata of Bundle Sheath Cells of C4 Plants

Bundle sheath cell strands have been prepared from four C₄ plantspecies and used to study the molecular weight exclusion limitof plasmodesmata located in the cell wall of bundle sheath cells.By measuring the activity and the inhibition of enzymes locatedwithin the bundle sheath cells of the strands in the absenceor presence of a variety of inhibitors of different molecularweight, the molecular weight exclusion limit of the plasmodesmatalocated within the cell walls of bundle sheath cells has beendetermined. Using a variety of Reactive dyes (of different molecularweight) which inhibit a number of cytosohc enzymes, as wellas a graded series of Reactive Yellow 2 derivatives as probes,it has been shown that compounds with molecular weights greaterthan about 900 daltons do not pass through the plasmodesmataof bundle sheath cells of C₄ plants. Key words: Plasmodesmata, molecular weight exclusion limit, bundle sheath cells     

Pulsed mode of a negative corona in nitrogen: II. Numerical calculations

A simplified model of a cathode sheath sustained by electron avalanches is presented. The model is used to calculate the pulsed mode of a negative corona in nitrogen in order to establish the physical picture of the processes occurring in a pulsed corona. The most important point is that, in the pulsed mode, both the averaged and dynamic current-voltage characteristics of a glow cathode sheath are found to have a negative slope. Lowering the degree to which the glow cathode sheath is subnormal (by sharply reducing the sheath area) or switching on additional ionization mechanisms (e.g., stepwise ionization) that force the cathode sheath to evolve into a prearc spot causes the negative slopes of the averaged and dynamic current-voltage characteristics of the sheath to become more gradual and even positive, thereby stabilizing the discharge current.