Meristem

By:Muhammad Salehuddin Ahmad

Nor Wahidah Hasim

1. Meristematic zones 1. Meristematic zones 2 .Apical meristems 2 .Apical meristems 2.1 Shoot apical meristems 2.1 Shoot apical meristems 2.2 Root apical meristems 2.2 Root apical meristems 2.3 Intercalary meristem 2.3 Intercalary meristem 2.4 Floral meristem 2.4 Floral meristem 2.5 Apical dominance 2.5 Apical dominance 3. Primary meristems 3. Primary meristems 4. Secondary meristems 4. Secondary meristems

A A meristemmeristem is a tissue in all plants consisting of is a tissue in all plants consisting of undifferentiated cells (undifferentiated cells (meristematic cellsmeristematic cells) and ) and found in zones of the plant where growth can take found in zones of the plant where growth can take place.place.

The term “meristem” was first used by Karl The term “meristem” was first used by Karl Wilhelm von Nägeli (1817-1891) from his book Wilhelm von Nägeli (1817-1891) from his book “Beiträge zur Wissenschaftichen Botanik” in “Beiträge zur Wissenschaftichen Botanik” in 1858. It is derived from the Greek word 1858. It is derived from the Greek word “merizein”, meaning to divide in recognition of its “merizein”, meaning to divide in recognition of its inherent function.inherent function.

Differentiated plant cells generally cannot Differentiated plant cells generally cannot divide or produce cells of a different type. divide or produce cells of a different type. Therefore, cell division in the meristem is Therefore, cell division in the meristem is required to provide new cells for expansion required to provide new cells for expansion and differentiation of tissues and initiation of and differentiation of tissues and initiation of new organs, providing the basic structure of new organs, providing the basic structure of the plant body.the plant body.

Apical meristems are the completely Apical meristems are the completely undifferentiated (indeterminate) meristems in a undifferentiated (indeterminate) meristems in a plant. These differentiate into three kinds of plant. These differentiate into three kinds of primary meristems. The primary meristems in primary meristems. The primary meristems in turn produce the two secondary meristem turn produce the two secondary meristem types. These secondary meristems are also types. These secondary meristems are also known as lateral meristems because they are known as lateral meristems because they are involved in lateral growth.involved in lateral growth.

Apical meristem

Shoot apicalmeristem

Root apicalmeristem

Intercalary meristem Floral meristem Apical dominance

The The apical meristemapical meristem, or growing tip, is a , or growing tip, is a completely undifferentiated completely undifferentiated meristematicmeristematic tissue found in the buds and growing tips of tissue found in the buds and growing tips of roots in plants.roots in plants.

function – to begin growth of new cells in function – to begin growth of new cells in young seedlings at the tips of roots and shoots young seedlings at the tips of roots and shoots (forming buds, among other things). (forming buds, among other things).

Apical meristems are composed of several Apical meristems are composed of several layers.layers.

The number of layers varies according to plant The number of layers varies according to plant type. In general the outermost layer is called type. In general the outermost layer is called the the tunicatunica while the innermost layers are the while the innermost layers are the corpuscorpus. .

Shoot apical meristemShoot apical meristem

is the site of most of the embryogenesis in is the site of most of the embryogenesis in flowering plants. flowering plants.

It is where the first indications that flower It is where the first indications that flower development has been evoked are manifested. development has been evoked are manifested.

Root apical meristemRoot apical meristem

root apical meristem produces cells in two root apical meristem produces cells in two directions directions

It is covered by the root cap, which protects It is covered by the root cap, which protects the apical meristem from the rocks, dirt and the apical meristem from the rocks, dirt and pathogens. pathogens.

Intercalary meristemIntercalary meristem

occur only in occur only in monocotmonocot (particularly grass) (particularly grass) stems at the base of nodes and leaf blades.stems at the base of nodes and leaf blades.

Intercalary meristems are capable of cell Intercalary meristems are capable of cell division and allow for rapid growth and division and allow for rapid growth and regrowth of many monocots. regrowth of many monocots.

Floral meristemFloral meristem

When plants begin the developmental process When plants begin the developmental process known as flowering, the shoot apical meristem known as flowering, the shoot apical meristem is transformed into an inflorescence meristem is transformed into an inflorescence meristem which goes on to produce the floral meristem which goes on to produce the floral meristem which produces the familiar sepals, petals, which produces the familiar sepals, petals, stamens, and carpels of the flower.stamens, and carpels of the flower.

Fig. 2. Expression pattern of two floral organ identity genes

Apical meristems may differentiate into three kinds Apical meristems may differentiate into three kinds of primary meristem:of primary meristem:

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

ProcambiumProcambium - lies just inside of the protoderm and - lies just inside of the protoderm and develops into primary xylem and primary phloem. It develops into primary xylem and primary phloem. It also produces the vascular cambium, a secondary also produces the vascular cambium, a secondary meristem. meristem.

Ground meristemGround meristem develops into the pith. It produces develops into the pith. It produces the cork cambium, another secondary meristem. the cork cambium, another secondary meristem.

There are two types of secondary meristems, There are two types of secondary meristems, these are also called the these are also called the lateral meristemslateral meristems because they surround the established stem of because they surround the established stem of a plant and cause it to grow laterally (i.e. a plant and cause it to grow laterally (i.e. larger in diameter).larger in diameter).

Vascular cambium - produces secondary Vascular cambium - produces secondary xylem and secondary phloem, this is a process xylem and secondary phloem, this is a process which may continue throughout the life of the which may continue throughout the life of the plant. This is what gives rise to wood in plants. plant. This is what gives rise to wood in plants. Such plants are called arborescent. This does Such plants are called arborescent. This does not occur in plants which do not go through not occur in plants which do not go through secondary growth (known as herbaceous secondary growth (known as herbaceous plants). plants).

Cork cambium - gives rise to the bark of a Cork cambium - gives rise to the bark of a tree. tree.

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