Cell sheath

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. 

Several members of the domain Bacteria have a capacity to form Mn(IV) oxides by oxidizing Mn(II), which some deposit on their cells, sheaths or appendages, or in the case of marine Bacillus sp. strain SG-1 on the surface of the spores this organism forms (see Ehrlich, 1999). In most cases the mineral type of the manganese oxide formed has not been well characterized. In the case of the free spores of Bacillus sp. strain SG-1, the nature of the mineral formed varies depending on culture conditions, such as Mn(II) concentration, ionic strength and temperature, under which the mineral was formed, and on mineral aging (Mandernack et al., 1995). The initial product of the Mn(II) oxidation by the spores is poorly crystallized. 

The cell sheath also contains other glycoproteins, the so-called cell adhesion molecules or CAMs, which have been implicated in the mediation of cell adhesion, A large number of such molecules have now been identified since the original work by Gerisch on slime mold (see Section 12.7). A list of these is given in Fig, 12,4, together with other molecules such as the nectins and... 

Anti-adhesive agents have been sought to prevent the sticking of the bacteria to teeth but generally these have not been successful, and bacteriocides are normally used. The problem is the mechanism of the bacterial adhesion, as shown in Fig. 12.25. It is thought that a fdm of polymer from saliva first attaches to the hydroxyapatite. Then bacteria attach to this coating. The bacteria produce a complex layer of cell sheath which glues the cells to each other. 

Recently, Jacobs and Gilbert (1983) succeeded in visualizing in pea stem tissue by means of an indirect immunofluorescence technique the presumptive auxin transport carrier in the plasma membranes at the basal ends of parenchyma cells sheathing the vascular bundles. 

Figure 16.1. Schematic drawing of a Drosophila ommaditium and whole-ceU light response. The pigment cells and photoreceptor cells are shown in longitudinal and transverse section. The pigment cell sheath is removed by the dissociation procedure allowing direct access to the photoreceptor membrane. The current inset shows a cartoon of a typical whole-ceU response to a Ught stimulus. The photoreceptor is clamped at -60 mV.

Wool fibers consist of cells, where battened ovedapping cuticle cells form a protective sheath around cortical cells. In some coarser fibers, a central vacuolated medullary cell type may be present. 

Cables with a copper sheathing are used only seldom. The protective cover is the same as with a corrugated steel-sheathed cable. If a cable with copper sheathing is connected to a lead-sheathed cable (A-PMbc) (see Table 13-1), the copper sheathing acts as a cathode in a galvanic cell and is therefore cathodically protected. 

The switching-off method for 7/ -free potential measurement is, according to the data in Fig. 3-5, subject to error with lead-sheathed cables. For a rough survey, measurements of potential can be used to set up and control the cathodic protection. This means that no information can be gathered on the complete corrosion protection, but only on the protection current entry and the elimination of cell activity from contacts with foreign cathodic structures. The reverse switching method in Section 3.3.1 can be used to obtain an accurate potential measurement. Rest and protection potentials for buried cables are listed in Table 13-1 as an appendix to Section 2.4. The protection potential region lies within U[[Pg.326]

Compartmentation of these reactions to prevent photorespiration involves the interaction of two cell types, mescrphyll cells and bundle sheath cells. The meso-phyll cells take up COg at the leaf surface, where Og is abundant, and use it to carboxylate phosphoenolpyruvate to yield OAA in a reaction catalyzed by PEP carboxylase (Figure 22.30). This four-carbon dicarboxylic acid is then either reduced to malate by an NADPH-specific malate dehydrogenase or transaminated to give aspartate in the mesophyll cells. The 4-C COg carrier (malate or aspartate) then is transported to the bundle sheath cells, where it is decarboxylated to yield COg and a 3-C product. The COg is then fixed into organic carbon by the Calvin cycle localized within the bundle sheath cells, and the 3-C product is returned to the mesophyll cells, where it is reconverted to PEP in preparation to accept another COg (Figure 22.30). Plants that use the C-4 pathway are termed C4 plants, in contrast to those plants with the conventional pathway of COg uptake (C3 plants). 

Component of the myelin sheath surrounding the axons of nerve cells. Additional compounds of the myelin sheath are phospholipids, cholesterol, cerebrosides, and specific keratins. The myelin sheath constitutes an isolating barrier during electrophysiological axonal signaling. 

The nodes of Ranvier are the gaps formed between myelin sheath cells along the axons. The sodium channels are densely localized at the nodes of Ranvier. 

Nitrous oxide dissolves in the fats that sheath the nerve cells, and produces numbing and mild intoxication. It is the laughing gas dentists use to make patients less aware of pain. 

In in sitn STM experiments the tip is immersed in the cell electrolyte. Electrochemical reactions can occnr on all the exposed metal snrface of the tip. It is important to snppress these electrochemical currents to valnes that are considerably less than the tunnehng current. This is done by sheathing all bnt a few micrometers at the end of the tip, with an insnlating layer of glass or polymer (Bach et al., 1993). 

Figure 11 The different steps of nitrogen metabolism in the extraradical hyphae, ccto-mycorrhizal roots, and roots of the host plant. I, absorption 2, assimilation 3. storage 4. translocation A, extramatrical hyphae B. ectomycorrhizal sheath C, Hartig net D, root cortical cells AA amino. acids.

InsAument parameters (sheath and auxiliary gas flows, spray voltage, capillary temperature, collision cell gas flow and offset, etc.) should be optimized while infusing a standard of tebuconazole prior to the Arst attempt at analysis. Optimization should be performed at an HPLC Aow rate and composition simulating those present during elution of tebuconazole using each HPLC condition set employed... 

The penis consists of three components, two dorsolateral corpora cavernosa and a ventral corpus spongiosum that surrounds the penile urethra and distally forms the glans penis. The corpora cavernosa consist of blood-filled sinusoidal or lacunar spaces, which are lined with endothelial cells, supported by trabecular smooth muscle, and surrounded by a thick fibrous sheath called the tunica albuginea. The caver-nosal arteries, which are branches of the penile artery, penetrate the tunica albuginea and supply blood flow to the penis. 

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