Sheath matrix

In 13 strains of cyanobacteria (from mostly freshwater and terrestrial habitats) grown under artificial UV (X,ma - 320 nm), MAA concentrations increase under UV exposure relative to controls under PAR alone (Table 15.5).132 A similar response occurs for MAAs in the sheath matrix of Nostoc commune.135,168 Additionally, the increased synthesis of extracellular MAAs is accompanied by an increased production of glycan that thickens the cellular sheath.168 In the cyanobacterium Chlorogloeopsis sp UV irradiation is not an obligate requirement for MAA synthesis.56 MAA synthesis in this species is not constitutive but is induced by UVB or increased osmotic stress (see also Section II.A. 10). 

Cell fractionation studies of five strains of cyanobacteria indicate that MAAs are located primarily (>90%) within the cytoplasm and not the cell sheaths, walls, or membranes.132 Extracellular placement of MAAs does occur in some cyanobacterial species that posses cellular sheath layers.134135 Extracellular MAAs are covalently bonded to oligosaccharide molecules embedded in the cyanobacterial sheath matrix and provide substantial protection to prevent photobleaching of chlorophyll within the cell. Intracellular or extracellular distributions of MAAs in eukaryotic cells have not been investigated. Based on the high MAA concentrations of Phaeocystis antarctica colonies, it has been suggested that MAAs are associated with the extracellular mucopolysaccharide matrix of the colony.125 This may be a more common phenomenon than currently recognized, and future research efforts will be necessary to further document extracellular occurrence of MAAs in cyanobacteria and algae. 

Most MAAs are intracellular, although MAAs can be translocated to external surfaces of cells and organisms because MAAs are found in significant concentrations in the extracellular sheath matrix of some cyanobacteria and in coral mucus.134 163 176 Scytonemin is not found intracellularly. It is located extracellularly in association with the glycan sheath but is not a structural component of the sheath layer.194 197 Scytonemin concentrations are not uniform within the sheath layer, and variations are related to the age of the sheath. In Scytonema myochrous, higher concentrations of scytonemin occur near the base of filaments where the sheath is older and thicker, while at newly formed apical cells, the sheath is usually absent or devoid of pigment.198... 

High-Voltage Sheaths Matrix and Child Law Sheath Models... 

Consider first the implantation current evolution during the sheath matrix phase, in the framework of the collisionless sheath model applied in the previous section (Lieberman Lichtenberg, 1994). This initial charge density in the matrix sheath is uniform therefore, the initial electric field varies linearly with distance x from the target (see Fig. 8-32) ... 

The picture of cement microstructure that now emerges is of particles of partially degraded glass embedded in a matrix of calcium and aluminium polyalkenoates and sheathed in a layer of siliceous gel probably formed just outside the particle boundary. This structure (shown in Figure 5.17) was first proposed by Wilson Prosser (1982, 1984) and has since been confirmed by recent electron microscopic studies by Swift Dogan (1990) and Hatton Brook (1992). The latter used transmission electron microscopy with high resolution to confirm this model without ambiguity. 

Clearly, combination of the crosslinking and mixed matrix approaches to produce a robust sheath layer with embedded molecular sieve domains is a hybrid option with potential application for high selectivity needed in aggressive environments. Such materials may be the ultimate low-cost option for many of the large-scale undeveloped markets. 

In essence, sea urchin larval spicule formation takes place in a preformed membrane framework that continuously changes. There is, however, also an organic matrix-like framework within the spiculogenic cavity. It is composed of polysaccharides and proteins that remain insoluble after the mineral phase of the mature spicule is dissolved [75]. The framework forms concentric sheaths around the spicule long axis, and has radiating fibers that connect the sheaths laterally. It is not, however, known whether this matrix is preformed and functions as a framework to guide the mineral deposition, or whether it is deposited periodically as the mineral is introduced. 

Figure 1. Scanning electron micrographs of (a) sheath of aligned matrix produced by low-pressure impregnation, and (b) transversely oriented matrix produced by high-pressure impregnation.

Appendageal structures commonly found within the skin are the hairs, hair follicles, associated sebaceous glands, apocrine and eccrine sweat glands, and arrector pili muscles. Hairs are formed by epidermal invaginations. These keratinized structures traverse the dermis and may extend into the hypodermis. The free part of the hair above the surface of the skin is the hair shaft, and the part deep within the dermis is the hair root, which forms an expanded knob-like structure called the hair bulb. This is composed of a matrix of epithelial cells in different stages of differentiation. Hair is composed of three concentric epithelial cell layers the outermost thin cuticle, a densely packed keratinized cortex, and a central medulla of cuboidal cells. The hair follicle consists of four major components (1) internal root sheath (internal root sheath cuticle, granular layer, pale epithelial layer) (2) external root sheath (several layers similar to the epidermis) (3) dermal papilla (connective tissue) and (4) hair matrix (comparable to the stratum basale of the epidermis). 

Capillary isoelectric focusing can be applied as a micropreparative tool for protein analysis by matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF-MS) [69,70]. The exact timing of the collector steps in the interface is based on determining the velocity of each individual zone measured between two detection points close to the end of the capillary. During the collection a sheath flow fraction collector is used to maintain the permanent electric current. 

Erosion and wax degradation also occurs in the cuticle of rice in contact with Helminthosporium oryzae germlings (AA) and the fungus produces excessive amounts of an extracellular matrix around germ tubes and appressoria. The extracellular sheath or matrix also was shown to adhere tenaciously to the cuticle and associated wax components. 

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