Meristematic tissue is group of immature cells that has capacity of division and redivision.
The term meristem was coined by Nageli (1858). Meristemsin plants are found in apex of stem, root, leaf primordia, vascular cambium, cork cambium, etc.
Characteristics of Meristematic Tissue:
1. They are composed of immature cells.
2. Absence of intercellular spaces.
3. Cells are oval, rounded or polygonal in shape.
4. Cells are always living and thin walled.
5. Cells are rich in cytoplasm with minute vacuoles.
6. Cell is diploid and shows mitotic cell division.
7. Cell is devoid of reserve food materials, ER and plastids.
Functions of Meristematic Tissue:
1. Meristems are actively dividing tissues of the plant.
2. They are responsible for primary (elongation) and secondary (thickness) growth of the plant.
3. All new organs and their growth occur by the division of meristematic tissue.
4. Secondary tissues such as, wood, cork are also formed due to activity of meristematic tissue.
Quiescent Centre or Quiescent Zone:
Clowes (1959) studied the root tips of Zea mays and observed an inactive centre in between root cap and meristematic region. He called it as Quiescent Centre.
1. It is a biconvex structure and made up of thousands of inactive cells.
2. In this region the rate of cell division is very slow as compared to surrounding cells.
3. This region carries less amount of DNA, RNA, ER, mitochondria and ribosomes.
4. This zone is the site of auxin synthesis.
Functions:
1. It acts as reservoir of cells.
2. It is more resistant to injury and irradiation.
3. If root growth is stopped or root tip is damaged then this zone restores the growth.