Cell walls parenchymatous

Feruloylated pectins have been found in the parenchymatous cell walls of many Dicotyledons (mainly in the Centrospermae and Solanaceae), but UV-fluorescence microscopy suggests that at least the epidermal cell walls of all Dicotyledons contain phenolic residues it remains to be seen whether these phenolic residues are attached to polysaccharides or to cutin, but location of even a small quantity of, say, feruloyl-pectin in the epidermal wall would be particularly significant in the control of growth because the extensibility of the epidermis controls the expansion of whole stems (23) and leaves (Fry, unpublished observations). The extensins, as already mentioned, are rich in the phenolic amino acid tyrosine (2). 

Pig. 55.—Cross-section through a portion o a root of A corns calamus. A, Cortical parenchyma Bt endodermis C, pericycle phloem F, xylem. At F Y, are large tracheal tubes, which were formed last, the narrow tubes near the periphery of the xylem being formed first. At the center of the root, within the circle of the radial vascular bundle, occur thin-walled parenchymatous pith cells. (From Sayre after Frank.)... 

In contrast to the cell walls of parenchymatous tissues of dicotyledons, those of cereal grains (wheat, barley, etc.) contain very little, or no, pectic substances. The primary walls of most cereal grains have cellulose microfibrils, which are closely associated with glucomannan, and these fibrillar structures are embedded in an amorphous matrix of hemicelluloses, which consists mainly of arabinoxylans and/or P-D-glucans, some of which are cross-linked by phenolic esters and/or proteins (Selvendran,... 

Suspension-cultured tissues of dicotyledons Cells containing mainly primary cell walls Same as parenchymatous tissues, except that the walls do not contain appreciable amounts of middle lamella pectins but have higher levels of polyphenolics and glycoproteins... 

Based on published work, as well as our experience, a two- or sometimes three-step extraction of the holocellulose, or depectinated cell walls in the case of parenchymatous tissues, is recommended, because it effects partial fractionation of the hemicelluloses. A first extraction with 5%... 

Feruloylated Pectins and Fendoylated Oligosaccharides. The cell walls of parenchymatous tissues of most grasses and some dicotyledons exhibit ultraviolet (uv) fluorescence (Harris and Hartley, 1981). The cell walls isolated from rapidly growing spinach cultures showed NH3-enhanced uv fluorescence (Fry, 1982b). We have found that the cell walls of parenchymatous (and lignified) tissues of sugar beet (root) and beetroot exhibited uv fluorescence. The cell walls isolated from parenchymatous tissues of beetroot also showed uv fluorescence. In contrast the cell walls of parenchymatous tissues of runner bean pods did not show uv fluorescence (R. R. Selvendran and P. Ryden, unpublished results). It would appear that the pectins (and other wall polymers) associated with ferulic and />-coumaric acids could be extracted from the cell walls of parenchymatous tissues (of dicotyledons) which exhibit uv fluorescence. 

In this chapter an attempt has been made to discuss the methods available for the isolation and analysis of higher plant cell walls. Because the structures and properties of the cell wall polymers from various tissue tyjDes show considerable differences, it is emphasized that, where possible, separation of the tissues in a plant organ prior to preparation of the cell walls is desirable. Attention is drawn to the problems associated with coprecipitation of intracellular compounds with cell wall polymers, particularly in view of the occurrence of small amounts of proteoglycan and proteoglycan-polyphenol complexes in the walls and the covalent attachment of phenolics and phenolic esters with some of the cell wall polymers of parenchymatous and suspension-cultured tissues. The preparation of gram quantities of relatively pure cell walls from starch- and protein-rich tissues is discussed at some length because of the importance of dietary fiber in human nutrition and an understanding of the composition, structure, and properties of dietary fiber would be hampered without such methods (Selvendran, 1984). 

The cell walls of springwood and latewood vessels retain crystalline cellulose for some time after the degradation front has passed. The same applies to clusters of parenchymateous cells in the earliest springwood and around vessels (Figure 19). In ash these cells have quite thick walls that obviously are more resistant than fiber cell walls. Together with the very thick walls of the latewood vessels, they are finally broken down from the lumen side (Figure 21). 

Laminal cells in frond leaves cell walls thin or weakly incrassate (prosenchymatous or in parts of the leaf parenchymatous) state 1 cell walls distinctly incrassate (collenchymatous) state 2. 

Pectic polysaccharides comprise -35% of the primary cell wall of dicots. The middle lamella, which lies between the primary walls of adjacent cells, is particularly rich in pectic polysaccharides. The amount of the pectic polysaccharides that can be extracted varies from 0.5%-1.5% from heavily lignified tissues to 15%-30% from parenchymatous and meristematic tissues in either case, only 50%-90% of the total pectic polysaccharides can be removed by direct extraction (see 152). 

Bark is composed of three layers an inner bark or phloem, a periderm layer, and an outer bark or rhytidome (110). Each of these layers can vary widely in appearance and thickness depending upon the tree, its age, and environmental conditions. The periderm layer consists of three cell types. The phellogen is the meristem that produces the phelloderm, a parenchymatous layer of cells produced internally, and the phellem, which is formed on the external side. The phellem cells are the cork cells that lay down a layer of suberin over the primary cell wall and seal off the cell, leading to eventual cell death. The anatomy of cork cells in bark has been reviewed by several authors (71, 73, 195, 295, 301, 312, 315, 320, 339, 344, 386, 432, 489, 490), and many of the woody plants whose periderm lay-... 

In addition, the parenchymatous cells in the xylem appear to yield at least two lignitic materials. One is a dark red-brown material that may be derived from inclusions originally present in the cell. This material is common and may be observed in Figures 2, 3, 5, 6, 7, and 8. The other coalified product associated with this cell type is yellowish in color and derived from the wall of the cell (Figures 2 and 6). Ray parenchyma and longitudinal xylem parenchyma typically form only a primary wall, and usually the wall is devoid of lignin. It is of interest that this wall layer is preserved and that it is frequently possible to observe the simple pits that are characteristic of this cell type (Figure 2). 

Seeds other than cereals Parenchymatous (e.g., cotyledons of peas) and some cells with thickened endosperm walls (e.g., guar) Same as parenchymatous tissues of dicotyledons Galactomannans and small amounts of cellulose, pectic substances, and glycoproteins... 

---