Meristematic Tissue

Meristematic tissues are a special type of tissues that possess undifferentiated cells that have the ability of cell division. Cells in the meristematic type of tissues can develop into all the other tissues and organs that occur in plants. Meristematic cells continue to divide until they get differentiated and then finally lose their ability to divide. So continue reading the article further in order to clear your concepts regarding meristematic tissues. The term meristem was first discovered in 1858  via  Carp Wilhem Von Nägeli in his book Beiträge zur Wissenschaftlichen Botanik (“Contributions to Scientific Botany ”). It is derived from the Greek word merizein which means “to divide”, in recognition of its inherent function.

Meristematic Tissues

Meristematic tissues, or meristems, are the tissues where the cells remain young and divide actively throughout the life of the plant. When a meristematic cell divides in two, the new cell that remains in the meristem are known as an initial, the other derivative. As new cells are added via repeated mitotic divisions of the initial cells, the derivatives is moved farther away from the zone of active division. These types of tissues stretch, enlarge and divides into other types of tissues as they mature. Meristematic cells are mainly small and cuboidal along with large nuclei, small vacuoles, and thin walls.

Differentiated plant cells usually divide and cannot divide or produce cells of various types. These cells are undifferentiated or incompletely differentiated. They are totipotent and are also capable of continued cell division. Division of meristematic cells helps in providing new cells for expansion and differentiation of tissues and also the initiation of new organs, thus providing a basic structure to the plant body. The cells of this type of tissues are small, with or without small vacuoles and protoplasm that fills the cell completely. The plastids(i.e. chloroplasts or chromoplasts) remains undifferentiated, but exists in rudimentary form (proplastids). Meristematic cells are packed closely together without the presence of any intercellular spaces. The cell wall is very thin and possess a primary cell wall.

Characteristics of Meristematic tissues

The characteristics of meristematic tissue are written as follows:

1. Meristematic Cells are small and generally cubical.

2. Their cell walls are thin and possess large nuclei.

3. Vacuoles are almost absent in meristematic tissues.

4. Cells are tightly packed with almost no intercellular spaces.

5. The new cells formed are transformed into mature permanent tissues.

6. They are mainly classified on the basis of origin, position, and function.

7. The cells of this tissue do not store food.

8. These tissues help in healing the injuries of an injured plant.

9. Meristematic tissues possess a high metabolic activity.

Types of Meristematic Tissues

The meristematic tissues are of the following types:-

On the basis of Origin:

Promeristem:

• This meristem possesses an embryonic origin.

• These are the youngest and earliest meristematic tissues.

• Promeristem are mostly present in growing roots and shoot tips.

• It usually gives rise to the primary meristem.

Primary meristem:

• It arises from Promeristem.

• Primary Meristem cells are always active and dividing in nature.

• These lie below promeristem in the shoot and root tip, and also in intercalary position.

• Primary Meristem gives rise to secondary meristem, and primary permanent tissue.

Secondary meristem:

• It arises from primary meristem.

• They develop later on in life.

• It leads to the formation of secondary permanent tissue.

On the basis of position:

Apical Meristem:

• These are present at apical parts of the plant like root tip and shoot tip.

• Apical meristem helps to increase the height of plants.

• It possesses two distinct zones:

• Promeristem zone: that comprises groups of dividing cells (apical initials).

• Meristematic zone: that comprises protodermis (epiderm), procambium (primary vascular tissue) and ground meristem (cortex and pith).

Intercalary Meristem:

• It is present in an intercalary position in the leaves and internodes.

• Intercalary meristem is a part of apical meristem.

• This also helps in increasing the height of plants.

• Mainly present in monocots, grass and pines.

Lateral Meristem:

• Lies on the lateral side of stem and root.

• Lateral meristem helps in increasing the diameter or thickness of plants.

• E.g. vascular cambium (primary meristem) and cork cambium (secondary meristem).

On the basis of function:

Protoderm:

• Its main function is to provide protection against mechanical injury.

• Protoderm tissues give rise to the epidermis layer.

• These are the outermost meristematic tissues.

Procambium:

• Its vital function is to transport water and nutrition.

• It leads to the formation of vascular tissue (xylem and phloem).

• These are the innermost meristematic tissues.

Ground meristem:

• It possesses various functions.

• They lead to formation of cortex, endodermis, pericycle and pith in dicot and hypodermis, and ground tissue in monocot.

Permanent Tissues

Permanent tissue cells are fully matured cells,  larger in size, and possess a specific shape. The metabolic rate of permanent tissue cells is relatively lower in comparison to other tissues. Meristematic tissues which take up a certain specific role lose their ability to divide. This process of taking up a permanent shape, size or a function is known as cellular differentiation. Cells of meristematic tissue differentiate in order to form different types of permanent tissues. There are mainly three types of permanent tissues: simple, complex and special permanent tissue.

Conclusion

Meristematic tissues are a special type of tissues that possess undifferentiated cells that have the ability of cell division. The meristematic tissues possess various characteristics. Meristematic tissues are of various types depending on origin, position and functions. We hope this article has helped you in understanding meristematic tissues in an easier way.