Of parenchyma cells

The bulk of potato tubers is made up of parenchyma cells that have thin, non-lignified, primary cell walls (Reeve et al., 1971 Bush et al, 1999, 2001 Parker et al., 2001). Unless stated to the contrary, potato cell walls refers to parenchyma cell walls. These walls and their component polysaccharides are important for a number of reasons they form part of the total intake of dietary fiber, influence the texture of cooked potato tubers and form much of the waste pulp that is produced in large amounts by the potato starch industry when starch is isolated. The pulp is usually used as cattle feed, but potentially could be processed in a variety of ways to increase its value (Mayer, 1998). For example, the whole cell-wall residues could be used as afood ingredient to alter food texture and to increase its dietary-fiber content, or cell-wall polysaccharides could be extracted and used in a similar way or for various industrial applications (Turquois et al., 1999 Dufresne et al, 2000 Harris and Smith, 2006 Kaack et al., 2006). 

Hardwood rays consist exclusively of parenchyma cells. The ray width varies in the tangential direction. In aspen wood the rays form one row, in birch wood and oak wood 1 -3 and 1 -30 rows, respectively. The height varies from one up to several hundred tiers. The rays account for 5-30% of the stem volume. 

The resin in the parenchyma cells is mainly composed of fatty acid esters (fats and waxes) and sterols. When wood is pulped, this resin usually remains encapsulated inside the parenchyma cells, while the oleoresin becomes dispersed in the liquor. This is particularly the case with spruce parenchyma cells, which have minute pores and rigid cell walls. Pine parenchyma cells have larger pores and release their resin more readily (Table 5-1). The resin content of acid sulfite spruce pulps can be effectively lowered by fiber fractionation. The situation is different for pine pulps in which the proportion of parenchyma cells is lower. 

Mean pit size at radial walls of parenchyma cells (p,m) 12 x 31d 2-3 (diam.)... 

Softwood species Volume % of wood Ray cells Parenchyma cells (%) Mean pit size of parenchyma cells (Atm)... 

TABLE 5-3. Characteristics of Parenchyma Cells in Hardwoods and the Formation of Heart wood"... 

On tree cross-sections, rays of parenchyma cells resemble spokes of a wheel as they extend from the bark into the wood, in the radial direction of the circular growth rings and perpendicular to the tangent of the rings or to the tangential direction (Fig. 28.2). Radial and tangential are both transverse directions, that is, horizontal to the trunk of the standing tree. 

Fibers and vessels die at an age of a few weeks, after attaining their final shape and chemical composition. Parenchyma cells live much longer, some remaining alive until sap-wood becomes heartwood. One of the tasks of parenchyma cells is to convert sugars into storage starch to serve as food reserves for the... 

P2 shows a similar distribution [11] — aligned cytosolic functions of C4 mesophyll cells with processes taking place largely in the cytosol of parenchyma cells of C3 plants, in particular sucrose synthesis [9,10]. 

These are bands of parenchyma cells which extend radially from the cortex to the pith (primary medullary rays) or from a part of the xylem to a part of the phloem (secondary medullary rays). In tangential-longitudinal sections they usually appear spindle shaped while in radial-longitudinal sections they are seen crossing the other elements. Their primary function is to supply the cambium and wood with elaborated sap formed in the leaves and conveyed away by the sieve tubes, and phloem parenchyma and to supply the cam-... 

Cortex, consisting of a broad zone of parenchyma cells many of which contain starch grains. 

Iferfw/fa orcomposed of parenchyma cells containing starch and often showing xylem patches cut off and enclosed within it. 

Transverse Section. The transverse section of southern yellow pine is normally quite simple and homogeneous. Its axial system is essentially composed of wood tracheids with only a relatively small number of parenchyma cells. An SEM micrograph of a transverse southern pine surface before exposure is shown in Figure 9. 

Within cross-sections of Tradescantia there is a regular distribution of both trilaminar epidermal complexes and vascular bundles within the leaf mesophyll. The leaf mesophyll consists of parenchyma cells which are uniform in size and shape. Initial exposure to simulated acid rain of pH 2,7 resulted in the collapse of outer epidermal cells in some areas. Distortion of underlying epidermal cells in the trilaminar sites and disruption of upper mesophyll cells also occurred. The next stage of lesion development varied slightly among lesions. In most lesions, collapse of mesophyll cells near the adaxial epidermis was evident. However, cell hypertrophy was also observed in about 50% of all lesions. Hypertrophic cells attained a cell volume three times that of unaffected cells. Supportive cells near vascular bundles were usually partially collapsed at this stage. 

Cotyledons of developing or germinating pea seeds contain two forms of glucan phosphorylase which are electrophoretically and immunologi-cally identical with the cytosolic (isozyme I) and the plastidic (enzyme III cf. 6) phosphorylase form from pea leaflets. For pea cotyledons the dual intracellular location of phosphorylase was ensured by indirect immunofluorescence. Using this technique, isozyme I was localized in the cytosol of parenchyma cells of cotyledons whereas the other isozyme was visualized in the stromal space of amyloplasts or proplastid-like organelles (data not shown). 

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. 

The problem is not easy to work on experimentally. Vascular development involves the differentiation of parenchyma cells in a developing organ into cell types very different from their neighbors. This occurs in highly symmetrical configurations within a matrix. Key questions for solution are what initiates, regulates, and maintains the spatial distribution of vascular cell formation within the stem, leaf, and root ... 

In 12 h imbibed Century cotyledon in which LOXl, 2 3 are present, the lipid bodies and protein bodies fill most of the cytoplasm in the cell. Using LOX antibody, immunogold label mostly appeared in the cytoplasm of parenchyma cells, with some present in protein bodies. No specific label was found in lipid bodies, mitochondria or cell walls. In four day germinated seedling cotyledons of Centuiy, lipid bodies and protein bodies were less predominant in storage parenchyma cells. Vacuoles appeared. 

Fig. 1 Electron micrographs of portions of parenchyma cells. Sections from 4-day germinated cotyledon of Century cross-reacting with soybean LOXl-3 antibodies. X 580,000, bar 0.25 pm. Abbreviations c cytoplasm lb lipid body.

The fibers encircling the vessels in Populus tremula show a chemotype with higher lignin content compared to fibers in fiber-rich regions [103]. In addition, an increased hgnin content was found in the narrow band of parenchyma cells at the annual ring [103]. This probably reflects the thick primary cell wall and the additional wall layer described for this cell type. 

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