Tissue sclerenchyma

Sclerenchyma Conductive tissue Sclerenchyma cells Mechanical support... 

Typical mature roots have different shapes (conical, conical-cylindrical, cylindrical, fusiform) and different sizes (3 to 15 centimeters in diameter), depending on variety, age and growth conditions. The color of the outer peel varies from white to dark brown. The cross-section of cassava roots shows the two major components which are the peel and the central pith (Figure 12.1). The peel is composed of the outer layer (called the periderm) and the inner layer (called the cortical region or cortex), which contains sclerenchyma, cortical parenchyma and phloem tissue. The large central pith of the roots is the starch-reserve flesh, comprised of cambium and parenchyma tissue and xylem vessels. 

Plants are predominantly composed of parenchyma and woody tissues. Parenchyma cells dominate the green tissues in leaves and are composed of a protein-rich protoplast surrounded by a cellulose wall. Woody plant cells dominate all support (sclerenchyma) and transport (xylem and phloem) stmctures in a plant. They are composed of several layers (middle lamella, primary wall, secondary wall, and tertiary wall) with varying proportions of cellulose, hemicellulose, and lignin (Fengel and Wegener, 1984). 

The most metabolic activity of plants is carried out in the tissue called parenchyma, which generally makes up the bulk of the volume of all soft edible plant structures. The epidermis, which sometimes is replaced by a layer of corky tissue, is structurally modified to protect the surface of the organ. The highly specialized tissues collenchyma and sclerenchyma provide mechanical support for the plant. Water, minerals, and products of metabolism are transported from one part to another of the plant through the vascular tissues, xylem and phloem, which are the most characteristic anatomical features of plants on the cross section. 

Ferulate 5-hydroxylase (F5H) catalyzes the third P-450 hydroxylation step at the C5 position of the phenolic ring to ultimately afford, via the monolignol pathway, 5-hydroxyconiferyl (22) and/or sinapyl (23) alcohols. This P-450 was first detected in xylem and sclerenchyma-enriched tissues from poplar Populus x euramericana), with microsomal extracts able to catalyze hydroxylation of ferulic acid (6) to 5-hydroxyferulic acid (7) in the presence of NADPH with apparent values of 6.3 pmoll / This enzyme was thus characterized as F5H. 

Both hardwoods and softwoods have cells (usually grouped into structures or tissues) that are oriented horizontally in the radial direction and which are called rays. The rays, composed of parenchyma with lignifled cell walls or sclerenchyma, connect various layers from pith to bark for storage and transfer of food. In softwoods, rays are one-cell thick. In hardwoods, they vary in size from one-cell wide and a few cells high to more than 15-cell wide and several centimeters high. Rays represent planes of weakness along which drying checks develop easily. 

Wheat straw is composed of different tissues that are more or less destroyable during the process. Leaves, intemodes, and the parenchyma (see Fig. 17.4) are more particularly destroyable. The sclerenchyma and the fibers networks are more resistant. 

In contrast to oil from plant tissue, the recovery of animal fat is not restricted by rigid cell walls or sclerenchyma supporting tissue. Only heating is needed to release fat from adipose tissue (dry or wet rendering with hot water or steam). The fat expands when heated, tearing the adipose tissue cell membrane and flowing freely. Further fat separation is simple and does not pose a technical problem (Fig. 14.1). 

Under the aspect of bioenergy feedstock, Sun et al. investigated the lignin and cellulose distribution in corn stover and eucalyptus by hyperspectral Raman imaging. In addition to the analysis of cellulose and lignin distributions in various tissue/cell types, this work is also focused on quantitative comparison of the tissue composition. As shown for corn stover stems, the cellulose content in sclerenchyma cells and tracheids is five times higher than in the parenchyma cells [79]. 

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