Meristematic Tissues 4x475f

MERISTEMATI C TISSUES MEENUJA .M.J NATURAL SCIENCE

INTRODUCTION     

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Tissues are group of similar cells Together carry out a specific function Called so, because of their identical fn Study – Histology Study in connection with a disease Histopathology Meristematic tissues are the tissues present in plant

MERISTEMATIC TISSUES 

Group of immature cells that are in a continuous state of division

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Found in those regions which need to grow continuously.

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Term “meristem” suggested by Nageli, 1858

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Also called formative tissue

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All permanent tissues are derived from meristematic tissues

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Plants produce new tissues and organs all thorough their life by this meristematic activity

CHARACTERS 

Capable of division and production of new cells.

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Usually isodiametric in shape

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Compactly arranged without intercellular spaces

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Cell walls are thin and cellulosic

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Abundant cytoplasm

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Prominent nucleus

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Do not store reserve food materials

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Vacuoles absent or very small

CLASSIFICATION 

Based on position  Apical

meristem  Intercalary meristem  Lateral meristem 

Based on origin  Promeristem  Primary

meristem  Secondary meristem

PROMERISTEM  Found in embryo  Also called primordial / embryonic meristem  These cells divide and give rise to primary meristem. Primary meristem – Apical & Intercalary  appear early in the life of a plant  responsible for the formation of primary plant body  Primary growth involves development of new parts of a plant and growth in length of a particular part  These cells divide and give rise to primary permanent tissues of the plant body.

SECONDARY MERISTEM 

Originates from permanent tissue during the course of growth

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Some of the permanent tissues regain their meristematic activity and become the secondary tissue

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Includes lateral meristems

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Increase the thickness of the plant body

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Also called as secondary thickening / secondary growth

APICAL MERISTEM

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present at the growing tips of stems and roots increases the length of the stem and root Responsible for primary growth Also called as growing point

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Apical meristem are composed of several layers

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1 - Central zone 2 - Peripheral zone 3 - Medullary (i.e. central) meristem 4 - Medullary tissue

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The number of layers varies according to plant type

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In general the outermost layer is called the tunica

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while the innermost layers are the corpus.

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The corpus and tunica play a critical part of the plant in physical appearance

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Apical meristems may differentiate into three kinds of primary meristem

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Protoderm - lies around the outside of the stem and develops into the epidermis.

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Procambium - lies just inside of the protoderm and develops into primary xylem and primary phloem. It also produces the vascular cambium

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Ground meristem develops into the pith. It produces the cork cambium

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These meristem are responsible for primary growth, or an increase in length or height

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Similarly in Root apical meristem

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quiescent center - The center of the root apical meristem is occupied by a quiescent center which has low mitotic activity

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calyptrogens (live root cap cells)

INTERCALARY MERISTEM  

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This meristem is located in between permanent tissues. It is usually present at the base of node, inter node and on leaf base. They are responsible for growth in length In angiosperms, intercalary meristems occur only in monocot (particularly grass) stems at the base of nodes and leaf blades.

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They are capable of cell division and allow for rapid growth and re growth of many monocots.

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Intercalary meristem at the nodes of bamboo allow for rapid stem elongation, while those at the base of most grass leaf blades allow damaged leaves to rapidly regrow.

LATERAL MERISTEMS 

Lateral meristems are found near the periphery of stems and roots and are responsible for increase in diameter

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known as secondary growth and secondary tissues

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This meristem consist of cells which mainly divide in one plane and cause the organ to increase in diameter and growth.

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Eg – cork cambium, interfascicular cambium

CONCLUSION 

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Meristmatic cells are the only dividing cell that present in plants They are present mainly in the tip of root and stem based on their position and origin they are classified in to many type.

All permanent tissues are derived from meristematic tissues