Meristematic tissue and its various types

Meristematic tissue and its various types

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  Plant Tissue Lecture-1 MeristematicTissue Introduction to tissue 1 Types of Plant Tissue 2 Characteristics of Meristematic Tissue 3 Various Types of Meristems 4 T O P I C S
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  Plant Anatomy Tissue: MeristematicTissue By: Dr. Sunita Sangwan Assistant Prof. Deptt. of Botany MNSGC Bhiwani
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  Introduction All living organismsare made up of basic units known as cells. The individual cells are grouped to form tissues that perform a specific function. The cells have distinctive shapes, wall characteristics and show specific physiological properties. Depending upon the organization of cells, tissues have been categorized into different types. In broad sense, a tissue may be defined as, “a group of similar or dissimilar cells that perform a common function and have a common origin.” Plant body comprises different functions and for this it has different tissue system. The various types of tissues are classified into three groups - meristematic, permanent and secretary tissues.
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  Meristematic tissue Initially allembryonic cells of an embryo have the capacity to divide and multiply but as the embryo develops into a plant body, this capacity for division is restricted to certain parts of the plant body called meristems which are active throughout the life of the plant body. When meristematic cells divide, a group of the daughter cells remains meristematic; the other daughter cells called derivatives differentiate into various tissue elements. Therefore, a meristematic tissue is a group of cells that are in continuous state of division or retain their power of division.
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  Characteristics of Meristematiccells 1. Meristematic cells may be rounded, oval or isodiametric in shape. 2. Compactly arranged i.e. no intercellular space and with dense cytoplasm. 3. Large nucleus, and small vacuoles or without vacuoles. 4. Cell wall is thin and do not store reserve food material. 5. Always in active state of division and divide in a plane.
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  On basis of origin Promeriste m Primary Meristem Secondary Meristem
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  Promeristem/ primordial/ embryonicmeristem  Group of cells, which represent primary stage of meristematic cells.  They are present in small region at the apices of shoots and roots.  The cells are thin walled isodiametric cells with dense cytoplasm and large nuclei.  They give rise to primary meristem.
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  Primary Meristem  Themeristematic cells that originate from promeristem and these cells are always in active state of division and give rise to permanent tissue.  It forms the fundamental parts of the plant and persists throughout the life of plant.  They are present below the promeristem at shoot and root apices.  These include apices of roots, shoots and primordial of leaves or other appendages.  In most monocots and herbaceous dicots, only primary meristem is present.
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  Secondary Meristem  Theyare the meristems developed from primary permanent tissue, which has undergone the dedifferentiation (After the differentiation some permanent cells regain the capability of division and this is known as dedifferentiation).  They are not present from the very beginning of the organ but develop at a later stage and give rise to secondary permanent tissue.  Secondary growth occurs due to these cells and plant increases in its diameter.  Cork cambium and vascular cambium are examples of secondary meristem.
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  Difference between Primaryand Secondary Meristem Primary Meristem Secondary Meristem 1. It originates from the promeristem or embryonic meristem of plant. 2. The cells of primary meristem are rounded, oval, polygonal and rectangular. 3. They do not possess central vacuoles. 4. The primary meristem give rise to primary permanent tissues of the plant body except intrafascicular cambium. 5. Examples: Protoderm, procambium and ground meristem. 1. It develop as a new meristem from the permanent tissues due to dedifferentiation. 2. The cells of secondary meristem are generally elongated. 3. They possess central vacuoles. 4. The secondary meristem give rise to secondary or supplementary tissues of the plants. 5. Examples: Vascular cambium, cambium of root, cork cambium and accessory cambium rings.
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  On the basis of position Apical Meristem Intercalary Meristem Lateral Meristem
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  Apical Meristem  Itlies at the apices of root, stem and often-in leaves as well.  Flowers also differentiate from apical meristem.  These are responsible for increasing the length of shoots and roots.  These cells always maintain their position and capacity to divide.  In higher vascular plants, apical cells are found in groups but in vascular cryptogams, it is found singly.
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  Intercalary Meristem  Thisis also a primary meristem, found inserted between permanent tissues, in the bases of internodes and leaf sheaths of grasses.  They originate from the apical meristem when their portions get detached due to growth of the organ.  Wherever stem is jointed, elongation of internodes is due to intercalary meristem as in Bamboos.  Even prolonged growth of leaves, flowers and fruits may be regarded as an intercalary growth.
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  Lateral Meristem  Itis located parallel to the long axis of root and shoot and predominantly divide periclinally.  They are responsible for increasing the diameter and form secondary permanent tissue.  Vascular cambium and cork cambium are the examples of lateral meristem.
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  Differences between ApicalMeristem and Lateral Meristem Apical Meristem Lateral Meristem 1. Apical Meristem is located at the growing apices of shoots and roots. 2. These are mostly primary meristems. 3. They are responsible for linear growth of organs. 4. e.g. Shoot apex and root apex 1. It is found on the sides of plant organs. 2. They are primary as well as secondary meristem. 3. The organ increases in diameter by their activity. 4. e.g. Vascular cambium, cork cambium
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  On the basisof plane of division Rib or File Meristem Plate Meristem Mass Meristem
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  • This meristemdivide at the right angles to the longitudinal axis of the plant organ, and therefore parallel files of cells are formed. • This meristem gives rise to cortex and pith of stem and root. Rib or File Meristem • It consists of parallel layers of cell which divide anticlinally in two planes so that a plate like structure is seen. • This meristem is present in leaf and increases the surface area without increasing the number of mesophyll layers. Plate Meristem • The cells of this meristem divide in all possible planes therefore, the tissue increases in volume. For example, embryo and endosperm. Mass Meristem
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  Meristem On the basisof Function Protoderm Procambiu m Ground meristem
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  Protoderm  The outermostmeristematic layer of the growing regions.  It is protective in nature and develops into outer dermal tissues including epidermis.  Stomata, trichomes and all glandular hairs develop from the protoderm.
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  Procambium  It consistsof narrow, elongated meristematic cells, which develop into primary vascular tissue.  The cells are densely cytoplasmic and consist of large nucleus.  In stem, the cells of Procambium develops primary xylem towards inner side and primary phloem towards outer side.  In dicotyledons stem, a portion of Procambium remains between primary xylem and primary phloem and later differentiates into cambium, which forms open collateral vascular bundles.
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  Ground meristem  Itis precursor of ground tissue and consists of large thin walled cells.  The cells develop into hypodermis, cortex, pericycle and pith.  This meristem is considered as the precursor of fundamental or ground tissue system.
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