MERISTEMATIC TISSUES

MEENUJA .M.J

NATURAL SCIENCE

INTRODUCTION 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

Found in those regions which need to grow continuously.

Term “meristem” suggested by Nageli, 1858

Also called formative tissue

All permanent tissues are derived from meristematic tissues

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

CHARACTERS

Capable of division and production of new cells.

Usually isodiametric in shape

Compactly arranged without intercellular spaces

Cell walls are thin and cellulosic

Abundant cytoplasm

Prominent nucleus

Do not store reserve food materials

Vacuoles absent or very small

CLASSIFICATION Based on position

Apical meristem Intercalary meristemLateral meristem

Based on origin PromeristemPrimary meristemSecondary 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

Some of the permanent tissues regain their

meristematic activity and become the secondary

tissue

Includes lateral meristems

Increase the thickness of the plant body

Also called as secondary thickening / secondary

growth

APICAL MERISTEM

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 Apical meristem are composed of several layers

1 - Central zone2 - Peripheral zone3 - Medullary (i.e. central) meristem4 - Medullary tissue

The number of layers varies according to plant type

In general the outermost layer is called the tunica

while the innermost layers are the corpus.

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

Apical meristems may differentiate into three kinds of primary meristem

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

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

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

These meristem are responsible for primary growth, or

an increase in length or height

Similarly in Root apical meristem

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

calyptrogens (live root cap cells)

INTERCALARY MERISTEM

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.

They are capable of cell division and allow for rapid

growth and re growth of many monocots.

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

known as secondary growth and secondary tissues

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

Eg – cork cambium, interfascicular cambium

CONCLUSION

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