meristem

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meristem

(mĕr`istĕm'), a specialized section of plant tissue characterized by cell division and growth. Much of the mature plant's growth is provided by meristems. Apical meristems found at the tips of stems and roots increase the length of these sections. Stems and roots may also grow in thickness or in diameter through cell divisions in lateral, or secondary, meristems, found just under the surface along the length of the stem or root. Tissues derived from differentiated lateral meristem are known as secondary tissues. In one type of lateral meristem, called cambium, or vascular cambium, the cells divide and differentiate to form the conducting tissues of the plant, i.e., the woodwood,
botanically, the xylem tissue that forms the bulk of the stem of a woody plant. Xylem conducts sap upward from the roots to the leaves, stores food in the form of complex carbohydrates, and provides support; it is made up of various types of cells specialized for each of
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, or xylem, and the phloem (see barkbark,
outer covering of the stem of woody plants, composed of waterproof cork cells protecting a layer of food-conducting tissue—the phloem or inner bark (also called bast).
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; stemstem,
supporting structure of a plant, serving also to conduct and to store food materials. The stems of herbaceous and of woody plants differ: those of herbaceous plants are usually green and pliant and are covered by a thin epidermis instead of by the bark of woody plants.
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). The growth in diameter of tree trunks is wholly dependent on the division of cambium cells. Other meristematic tissues include corkcork,
protective, waterproof outer covering of the stems and roots of woody plants. Cork is a specialized secondary tissue produced by the cork cambium of the plant (see meristem, bark).
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 cambium, which divides to produce waterproofing and protective cork tissue at the surface of the stem and root; and intercalary meristems, modified apical meristems found in different positions than either apical or lateral meristems, e.g., in the stem nodes of grasses. See also differentiationdifferentiation,
in biology, series of changes that occur in cells and tissues during development, resulting in their specialization. This, in turn, permits a greater variety of organisms.
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, in biology.
The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Meristem

 

formative tissue, a plant tissue characterized by prolonged cell-division activity. Some cells of the meristem—the initiating cells—remain in the embryonic phase of development and, by dividing, provide uninterrupted growth of the plant body. Other cells of the meristem gradually become differentiated, forming various derivative tissues (integumentary, conducting, mechanical, basal).

Meristems originate from the protomeristem of the embryo, which develops into the apical and lateral meristems. The apical meristems—the growing points of shoots and roots—are formed very early in the embryo. The formation of the cotyledons and later of the leaf rudiments on the growing point of the shoot results in differentiation of the lateral meristems into the procambium and cambium. Meristematic tissue is partially preserved in some parts of the plant body during plant growth, for example, in the roots (Pericycle—rhizogenic meristem), the nodes of the shoot, and the medullary rays of the stem. Intercalary meristem is temporarily preserved in the buds, the inter-nodes of the shoot (Gramineae), and the bases of the petioles.

Because almost all living, mature tissues (except the sieve tubes) possess the capacity to divide, new, or secondary, meristems, such as Phellogen (forming cork tissue) and callus, may arise in the plant. Meristem cells differ from the cells of permanent tissues in that they are smaller, densely arranged, and almost cubical in shape (only cells of the procambium and cambium are elongated). They usually have a thin primary membrane and a dense protoplast, in which the nucleus and nucleolus occupy a central position. The endoplasmic network is poorly developed; there are many ribosomes. The mitochondria and dictyosomes are only slightly differentiated. The vacuoles are very small, and the plastids are in the form of protoplastids. Meristem cells are characterized by high metabolic activity.

REFERENCES

Esau, K. Anatomiia rastenii. Moscow, 1969. (Translated from English.) Lehrbuch der Botanik fur Hochschulen, 30th ed. Jena, 1971.
I. S. MIKHAILOVSKAIA
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

meristem

[′mer·ə‚stem]
(botany)
Formative plant tissue composed of undifferentiated cells capable of dividing and giving rise to other meristematic cells as well as to specialized cell types; found in growth areas.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Grass grows back after being cut because the meristematic tissue is located beneath the path of the mower blade.
These dicots have meristematic tissue at the top of the stem.
And the meristematic tissue of root tips (about 2 mm length of the root tips) were dyed by carbol fuchsin and used for cytological observation.
In the sense, protocorm stage is featured by the development of the zygote embryo, which may be an explant used to induce somatic embryogenesis, since its structure has juvenile and meristematic tissues.
Independent on the solitary or colonial feature, gall induction usually occurs in meristematic tissues (Mani, 1964; Alvarez, 2011; Dias et al., 2013a; Ferreira & Isaias, 2014; Fleury et al., 2015), but there are some cases in which parenchymatic or epidermal tissues are the oviposition sites (Oliveira & Isaias, 2010b; Ferreira & Isaias, 2013).
Ca deficiency restrains the growth of meristematic tissues and youngest leaves would become deformed and chlorotic (Marschner, 1995).
It involves in many physiological, biochemical processes including respiration; formation of meristematic tissues [2], regulation of metabolic pathways [3] metaboli-zation of carbohydrate [4, 5], RNA and indole acetic acid [4, 5, 6, 7].
For this reason grasses, and grass-like plants typically exhibit abrupt transitions from fully developed stiff to weak meristematic tissues within a short distance at every node.
Occurring as it does in meristematic tissues, auxin is apparently responsible for the rapid growth and elongation of tissues, and in the shoot apex it diffuses downward and causes the stem to elongate.
Moose forage selectively on photosynthetic and meristematic tissues of a few preferred species.
Earlier, Fahn (1967) also pointed out that if these two meristematic tissues are present in one plant, they could be two developmental phases of the same meristem.