Vascular tissue xylem

Veins penetrate the mesophyll layers of a leaf. Veins consist of vascular tissue, xylem, and phloem, and con-... 

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. 

Distribution of compounds in barley and wheat tissues. Tissues of barley and wheat leaves were mechanically separated under the microscope. It was observed that in barley gramine was more concentrated in the epidermis than in the entire leaf (Table II). Hydroxamic acids in wheat were absent in epidermic tissues and were more concentrated in the vascular tissues than in the entire leaf. Neither compound was detected in xylem exudates nor in guttation drops. 

WOOD. A vascular tissue which occurs in all higher plants The most important commercial sources of wood are the gymnosperms, or softwood trees and the dicotyledonous angiosperms, or hardwood trees. Botanically, wood serves the plant as supporting and conducting tissue, and it also contains certain cells which serve in the storage of food. The trunks and branches of trees and shrubs are composed of wood, except for the very narrow cylinder of pith in the center and the bark which covers the outside. Botanists refer to wood by its Greek name, xylem. 

There are three types of tissue that make up all of these plant parts. The dermal cells are the densely-packed outer layer, which varies in thickness in different plants. The cells in this layer may secrete a waxy coating or cuticle that helps reduce the amount of water lost through a plant s exposed surfaces. The ground tissue is the body of the plant. And vascular tissue is made up of the specialized cells that transport water, minerals, food, and hormones throughout the plant Vascular cells are divided into xylem, which transport water and minerals from roots to the upper plant, and phloem, which takes food (sugars) from the leaves to the rest of the plant. These two types of cells are usually arranged in parallel, concentric form, with the phloem on the outside. 

The starch sheath is the innermost layer of the cortex (c), of which the outer cells have chloroplasts, in contrast to the surface layer, epidermis (e). In (A) the xylem (x) forms the vascular tissues together with the phloem. The longitudinal section in (B) is oriented along the line between the arrows indicated in (A). For methods, see.18 Size bars equal 25 pm in (A,B) and 2.5 pm in (C). 

Immediately inside the endodermis is the pericycle, which is typically one cell thick in angiosperms. The cells of the pericycle can divide and form a meristematic region that can produce lateral or branch roots in the region just above the root hairs. Radially inside the pericycle is the vascular tissue. The phloem generally occurs in two to eight or more strands located around the root axis. The xylem usually radiates out between the phloem strands, so water does not have to cross the phloem to reach the xylem of a young root. The tissue between the xylem and the phloem is the vascular cambium, which through cell division and differentiation produces xylem (to the inside in stems and older roots) and phloem (to the outside in stems and older roots). 

Figure 19 SEM and energy dispersive analysis micrographs (175x) showing mineral distribution, Ca, Si, and Al, localization in a frozen, planar transverse section 1 mm behind the tip in a second year needle of Pinus strobus (Eastern white pine) (a) secondary electron image, (b) calcium distribution, (c) Si distribution, and (d) Al distribution. Abbreviations endodermis (en), epidermis (ep), hypodermis (hy), mesophyll (me), transfusion tissue (tr), vascular tissue (vt), and xylem wall (xw) (courtesy of M. J. Hodson and A. G. Sangster, unpublished collection).

Venation is the pattern of veins in the blade of a leaf. The veins consist of vascular tissues which are important for the transport of food and water. Leaf veins connect the blade to the petiole, and lead from the petiole to the stem. The two primary vascular tissues in leaf veins are xylem, which is important for transport of water and soluble ions into the leaf, and phloem, which is important for transport of carbohydrates (made by photosynthesis) from the leaf to the rest of the plant. 

Monuron absorbed by the leaves is uniformly distributed in the leaf tissues, accumulating in the vascular tissues, but it is translocated only into the xylem (Pickering, 1965). 

The capillary and porous system of the body exists in vascular tissue and intercellular spaces. Xylem forms an open conduit of relatively low hydraulic resistance that is filled with diluted mineral solution. Phloem exists in cells with a width ranging from 10 to 70 pm and a length from 100 to 500 pm in dicotyledons [4]. Their turgor is around 2 MPa (beetroot is 1.83 MPa) with a pressure gradient of 0.02-0.03 MPa/m [5,6]. As phloem transports substances of very different molecular weight, shape, charge, and surface activity along with water, it is presumed that the mechanism is an osmotically driven solution flow [6]. 

Jacobs WP, McCready CC (1967) Polar transport of growth regulators in pith and vascular tissues of Coleus stems. Am J Bot 54 1035-1040 Jacobs WP, Morrow IB (1957) A quantitative study of xylem development in the vegetative shoot apex of Coleus. Am J Bot 44 823-842 Jacobs WP, Morrow IB (1967) A quantitative study of sieve tube differentiation in vegetative shoot apices of Coleus. Am J Bot 54 425 31 Jacobs WP, Danielson J, Hurst V, Adams P (1959) What substance normally controls a given biological process II. The relation of auxin to apical dominance. Dev Biol 1 534-554... 

Thompson NP, Jacobs WP (1966) Polarity of lAA effect on sieve-tube and xylem regeneration in Coleus and tomato stems. Plant Physiol 41 673-682 Torrey JG (1953) The effect of certain metabolic inhibitors on vascular tissue differentiation in isolated pea roots. Am J Bot 40 525-533 Torrey JG, Loomis RS (1967) Auxin-cytokinin control of secondary vascular tissue formation in isolated roots of Raphanus. Am J Bot 54 1098-1106 Torrey JG, Fosket DE, Hepler PK (1971) Xylem formation A paradigm of cyto-differen-tiation in higher plants. Am Sci 59 338-352... 

Wareing PF, Hanney CEA, Digby J (1964) The role of endogenous hormones in cambial activity and xylem differentiation. In Zimmermann MH (ed) The formation of wood in forest trees. Academic Press, London New York, pp 323-344 Wetmore RH, Rier JP (1963) Experimental induction of vascular tissues in callus of angiosperms. Am J Bot 50 418-430... 

The existence of a closed circulatory system in higher animals provides the organism with an easy and efficient route for the transport of hormones from the site of synthesis to the target tissues. In plants some hormones appear to be transported directly in the vascular tissue for example, cytokinin, GA, and ABA move from the root to the shoot in the xylem GA moves out of young leaves in the phloem and ABA is transported out of wilting leaves in the phloem (Fig. 6.1). However, auxin is not transported directly in the vascular tissue, but instead appears to be transported in cells associated with the phloem (Fig. 6.1). Ethylene poses a special problem in that it is a diffusable gas. However, its precursor, 1-aminocyclopropane-l-carboxylic acid (ACC), is transported from the root to the shoot in the xylem. Therefore, using the traditional concept of a hormone as a translocated chemical messenger, ACC may be more aptly considered to be a hormone than ethylene. 

Porandowski J, Rakowski K, Wodzicki TJ (1982) Apical control of xylem formation in pine stems. II. Responses of differentiating tracheids. Acta Soc Bot Pol 51 187-201 Sachs T (1969) Polarity and induction of organized vascular tissues. Ann Bot 33 263-275 Schmid R (1965) The fine structure of pits in hardwoods. In Cote Jr (ed) Cellular ultrastructure of woody plants. Syracuse Univ Press, Syracuse, pp 291-304... 

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