Meristematic tissues

Meristematic Tissue- Definition and Function

Introduction

Meristematic tissue is any plant tissue that consists of undifferentiated cells that can undergo rapid cell division. These rapidly growing tissues are found at the tips or apices of plant organs. They are responsible for producing new cells and tissues required by growing plants, such as buds, roots, leaves, and flowers. Meristematic tissues are also known as apical, regressing, or intercalary meristems.

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Types of Meristematic Tissue

Meristematic tissues are characterized by localized regions of high cell division rates. In vascular plants, they include:

Primary Meristems

Primary meristems are the first set of meristems that develop. During this process, cells divide rapidly and without any differentiation until organ primordia have been formed. The primary meristem is responsible for the growth of cells in the tips, roots, and leaves’ surface. The cells will then differentiate into other types of plant tissue.

Primary meristems are the first meristem to develop. There are three major types: axillary, intercalary, and apical. These are responsible for growth throughout a plant’s life.

Axillary Meristem

Figure: Axillary buds on a plant

The axillary meristem is located in the angle between a stem and leaf, usually on a plant’s twigs. This type of meristem causes the angle between a stem and leaf to become sharper as it develops.

Axillary meristems occur when a plant branch develops into a new shoot. The region between the petiole and stem of a leaf is also an example of this type of meristem.

This meristem is composed of undifferentiated cells that undergo rapid cell division. The cells are located inside the vascular cylinder and are lined with cork cells. They continue to divide until a growth center, or bud is formed.

Intercalary Meristem

Figure: Location of an intercalary meristem

An intercalary meristem contains actively dividing cells that have the potential to form aerial parts. It is found between the nodes of grasses and between the internodes of bamboo. Intercalary meristematic cells elongate to create new leaves, flowers, roots, branches, and the new growing point (apical meristem).

As new cells are produced, older cells die off, thus increasing the length of a plant. The cells produced in this type of meristem may or may not have secondary walls. The nodes are farther apart than in other plants with meristems. The cells produced may also be fluted or mitrate (as in some grasses).

Apical meristem

Apical meristem participates in the elongation of stems, roots, and leaves (apices). It is usually located at the tip of a stem or root, called an apical bud.

Apical meristems also contribute to the expansion of the organism. They divide to increase the surface area (by increasing leaf and branch size). Also, they cause thickening in dicots through secondary growth, making the plant’s tissues wider instead of longer.

The apical meristem is further divided into root apical, shoot apical, intercalary meristem, floral meristem, and gametophyte apical meristems.

Root Apical Meristem

The apical root meristem produces all the cells in a growing root. Mature roots do not have an apical meristem but remain meristematic at the root tip. For example, in dicots, lateral roots arise from the root apical meristem.

As the root grows, the meristem remains to produce cells that elongate and thicken into the secondary wall. The root apical meristem is responsible for the elongation of roots, and it does this by division. This cell division is high-speed due to excessive amounts of cell division factors.

Shoot Apical Meristem

The Shoot apical meristem produces all the cells in a growing shoot, including leaves and lateral buds. Within the apical meristem, stem cells are produced, which divide to increase the surface area (by increasing leaf and branch size).

The shoot apical meristem is also called the apical bud. The stem is the shoot. The apical meristem with two leaves is still called an apical bud, even though there are two leaves.

The apical meristematic tissue is responsible for the growth of each leaf, and it does this by division into smaller cells.

Floral Meristem

The floral meristem is a type of apical meristem. It produces the meristematic cells found in the apical meristem of a flower. This tissue contains three different kinds of cells: undifferentiated cells capable of producing other types of cells, the meristematic cells, and the terminal cells.

This type of meristematic tissue is responsible for the growth of the stem, leaves, and floral organs. Unlike most other tissues in a plant’s life cycle, meristematic cells, once formed, remain in the same position the rest of their lives unless they are actively dividing.

The terminal cells will eventually become petals, whereas the meristematic cells will become sepals. The undifferentiated cells are found in areas adjacent to the floral meristem. They will become the stamens and carpels in flower. The growth of the floral meristem is regulated by hormones such as auxin, which promotes cell division.

Gametophyte Apical Meristem

The gametophyte apical meristematic tissue produces cells that give rise to the cells of gametophytes. The cells that give rise to the gametophyte are called sex cells or gametes. Those cells are diploid, which means that they have two copies of each chromosome.

The gametophyte apical meristem is also known as the microspore mother cell. It is surrounded by several cells called the tapetum. These cells are usually involved in food production, but they will become the protective covering of the sporophyte.

For example, the sporophyte of moss plants is a capsule of two layers. The outermost layer is made of the tapetum. In seed plants, the tapetum is a layer of cells surrounding the microspores.

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Secondary Meristems

Secondary meristems are actively dividing cells that produce new plant tissue to replace or repair the existing part. They are also called lateral meristems and are found in the roots and stems of a plant. They are vascular cambium, cork cambium, and cork papilla.

Lateral meristems are created by specialized cells that divide rapidly to form new cells. The cells in secondary meristems are undifferentiated and can form many kinds of plant tissue.

Vascular Cambium

The vascular cambium is a type of secondary meristem that produces two new layers of cells. The vascular cambium is always located just inside the bark on the inner surface of a woody stem. Secondary meristem has the vascular tissues that transport water and nutrients to and from the leaves in a plant.

The vascular cambium is a cylinder of undifferentiated cells. These cells produce xylem to the inside and phloem to the outside. This meristematic tissue forms during the summer months in many species, and its development is regulated by auxins, which stimulate cell division.

Cork Cambium

The cork cambium is a meristem found in the stem of plants that produces bark. It is always located just outside the periderm and produces two types of cells, cork cells, and phelloderm.

The term cork refers to the protective outer covering of a plant. The type of bark produced depends on the species. The cork cambium is a specialized meristem that forms on the tissue just outside the periderm. It makes the bark of a plant.

This meristem also produces undifferentiated cells, but some will differentiate into phellem cells, becoming the outer bark.

Cork Papilla

The cork papilla is a rounded structure that develops on the cork cambium of a plant. It develops into a single layer of dead cells at first, but then it develops into cork cells. This type of secondary meristem develops into the bark with multiple layers. It also forms rings in some plants.

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What are Induced Meristematic Tissues?

Induced meristematic tissues are plant organs that have meristematic cells. These tissues are formed through artificial treatment. The new tissues formed by this treatment are not genetically identical to the original tissue. Examples of Induced meristematic procedures are:

Budding and Grafting

Figure: Steps of grafting

It is one of the simplest methods of inducing meristematic tissues. A plant branch is removed and inserted in an incision made in another plant’s branch or trunk. The branches will fuse, and new growth will also appear at the incision site in the plant with a branch inserted into it. The new tissues are the cambium of the branch and a layer of epidermal tissue.

In vitro plant regeneration

This method involves the use of meristematic cells that are grown in an artificial environment to induce growth. The cells can be isolated from the meristem of an immature embryo or the meristem of a mature plant.

The cells are grown in liquid media and passaged for several generations. This is done so that the cells are genetically identical and produce many plants at once. The process of in vitro plant regeneration is used to grow genetically modified or transgenic plants.

Beads of Meristem Tissue Culture (Micropropagation)

This method of induction involves growing meristem tissue on semi-solid media. It is used to produce genetically identical plants in large amounts.

During micropropagation, the meristematic cells are attached to small beads of agarose. This allows the plant hormones and growth regulators to diffuse throughout each of the meristematic cells in the liquid media.

Somatic embryogenesis

Figure: Steps of somatic embryogenesis

Somatic embryogenesis is the process of creating a plant from non-genetically identical meristem tissues.

The first step during somatic embryogenesis is to remove the egg cell from the ovary and insert immature embryos in liquid media culture. After this, the cells are treated with plant growth regulators to induce growth.

This process has been done using seedy plants, but it has also been achieved in plants with no seeds. The advantage of creating a plant from meristem tissues instead of seeds is that the plant will grow without developing a whole new set of meristem tissue.

Also, if a plant is genetically modified, adding the new gene to some meristematic tissue will allow it to pass on that gene in all its cells.

Tissue recombination (Transformation)

The process of inducing meristematic cells is different from the normal processes of meristem development. This process provides a way to produce plants with specific characteristics, such as increased disease resistance.

Tissue recombination is used to create transgenic plants. The genetic makeup of the plant cells is modified by inserting a piece of DNA with new traits into the cell.

This insertion may be done via the use of viruses or naked DNA. Transgenic plants can be created using this method that have traits removed from other plants or engineered into the plant.

The benefit of creating transgenic plants can produce plants with specific traits that may help eliminate world hunger or diseases.

Apical Dominance Explained

Apical dominance is a form of plant control in which the shoot tip determines the growth of shoots and roots.

This control occurs when the terminal bud of a plant is removed or dies. Removing the terminal bud causes lateral buds to become dominant instead of the terminal bud. Also, leaves near the terminal bud will grow faster than those that are further down the stem.

Apical dominance is beneficial to farmers because it increases the number of lateral buds on a plant. They may do this by removing the terminal bud from some plants or pruning the shoot tip.

General Functions of Meristematic Tissues

Meristematic tissues have the following functions:

  • They produce shoots and roots from undifferentiated plant cells.
  • They are the sites of growth in plants that do not have seeds or flowers.
  • These tissues allow plants to grow and develop new meristematic tissues.
  • Meristematic tissues enable plants to produce new leaves and roots each season.
  • They provide a way for plants to start growing from cuttings.
  • These tissues enable the growth of plants under laboratory conditions (in vitro).

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Summary

Meristematic tissues are the plant structures that have cells that can divide to produce more plant parts. They are found in the roots, stems, and leaves of plants. These tissues allow for growth and adaptation to respond to changes in an environment or other stimuli such as damage caused by pests. This blog post has examined what meristematic tissue is, how it functions, where you find them on a plant’s body, their types (apical/lateral), and why they’re essential to plants’ survival.

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