Apical meristem, region of cells capable of division and growth in the root and shoot tips in plants. Apical meristems give rise to the primary plant body and are responsible for the extension of the roots and shoots. Unlike most animals, plants continue to grow throughout their entire life span because of the unlimited division of these and other meristems.

1. Apical Meristem
Dr. Naveen Gaurav
Associate Professor and Head
Department of Biotechnology
Shri Guru Ram Rai University
Dehradun

2. Apical meristem, region of cells capable of division and growth in the root and shoot tips
in plants. Apical meristems give rise to the primary plant body and are responsible for the
extension of the roots and shoots. Unlike most animals, plants continue to grow
throughout their entire life span because of the unlimited division of these and
other meristems.
Longitudinal section of an apical meristem

3. As in other meristematic regions, the cells of the apical meristems are typically small and nearly
spherical. They have a dense cytoplasm and relatively few small vacuoles (watery saclike enclosures).
Some of these cells, known as initials, maintain the meristem as a continuing source of new cells and
may undergo mitosis (cell division) many times before differentiating into the specific cells required for
root or shoot growth. The cells that emanate from the apical meristem are arranged in lineages of
partially differentiated tissues known as primary meristems.
There are three primary meristems: The protoderm, which will become the epidermis; the ground
Meristem, which will form the ground tissues comprising parenchyma, collenchyma,
and sclerenchyma cells; and the procambium, which will become the vascular tissues
(xylem and phloem).
root and shoot apical meristems: The shoot apical meristem of Hypericum uralum (left) appears at the topmost aspect of the stem.
Immediately behind the apical meristem are three regions of primary meristematic tissues. The root apical meristem (right) appears
immediately behind the protective root cap. Three primary meristems are clearly visible just behind the apical meristem.

4. Root Apical Meristem
The root apical meristem, or root apex, is a small region at the tip of a root in which all cells
are capable of repeated division and from which all primary root tissues are derived. The
root apical meristem is protected as it passes through the soil by an outer region of
living parenchyma cells called the root cap. As the cells of the root cap are destroyed and
sloughed off, new cells are added by a special internal layer of meristematic cells called the
calyptrogen. Root hairs also begin to develop as simple extensions of cells near the root
apical meristem. They greatly increase the surface area of the root and facilitate the
absorption of water and minerals from the soil.
Beginning with the root cap and leading away from the root tip, there are three distinct
zones in which certain specific growth patterns dominate: cell division, cell elongation, and
differentiation and tissue maturation. There is a gradual transition between these regions.
The region of cell division includes the apical meristem and the primary meristems—the
protoderm, ground meristem, and procambium—derived from the apical meristem. As is
generally true of nonmeristematic regions elsewhere in the plant body, root length in the
second region is increased as a result of cell elongation rather than by cell division. The
region of differentiation and tissue maturation that follows is where the
cells differentiate (i.e., change in structure and physiology into cells of a specific type) and
where the first primary phloem and xylem, as well as mature root hairs, are clearly seen. In
plants with woody roots (i.e., those of perennial dicotyledons), secondary growth, including
secondary xylem and phloem as well as the periderm, are developed and add girth to the
plant.

5. Shoot Apical Meristem
All the branches and stems of higher vascular plants terminate in shoot apical meristems.
These are centres of potentially indefinite growth and development, producing the leaves as
well as a bud in the axis of most leaves that has the potential to grow out as a branch. These
shoot apical growing centres form the primary plant body.
Shoot meristems in some species may interconvert and change the type of shoot they
produce. For example, in the longleaf pine (Pinus palustris), the seedlings enter a grass stage,
which may last as long as 15 years. Here the terminal bud on the main axis exists as a short
shoot and produces numerous needle-bearing dwarf shoots in which there is little or no
internode elongation. Consequently, the seedling resembles a clump of grass. This is
probably an adaptation to fire, water stress, and perhaps grazing. The root volume, however,
continues to grow, increasing the chance of seedling survival once the shoot begins to grow
out (i.e., the internodes start to expand). This process is called flushing.
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