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BIOL 100C:
Introductory Biology III
Primary Growth in Roots and
Stems
Dr. P. Narguizian
Fall 2012
Principles of Biology
Vascular and Ground Tissue
• The majority of tissue in a plant stem is called ground tissue and
basically fills the space around the vascular tissue.
• The three types of ground tissue: parenchyma, collenchyma and
sclerenchyma.
• -enchyma = root word means 'cellular tissue.' Parenchyma is the
most common form of tissue in plants and provides a variety of
functions, including the storage of food and water. Collenchyma
tissue helps support young stems and roots. Lastly, sclerenchyma
tissue provides rigid support and protection for the plant stem. The
Greek term sclera means 'hard.' This can help you remember that
sclerenchyma is hard tissue that provides rigid support.
Shoot System Review
• The shoot system is the above-ground
structure of plants including the leaves,
buds, stems, flowers and fruits of plants.
We'll focus on the growth of the stem for
now, but later on we'll look at other plant
structures.
Plant Anatomy
Figure 5 Shoot system (Nodes & Buds).
• The main function of the leaves and stemswhich together constitute a plant's shoot
system-is harvesting sunlight.
• The stem of a vascular plant supports the
plant, stores nutrients, generates new tissue,
and makes and supports leaves.
• The stem of a vascular plant makes leaves at
special sites called nodes. Between two
nodes is a segment called an internode.
Together, they make up the majority of the
stem.
• In eudicots, the very tip of a stem, where
most growth occurs, is called the apical bud
(terminal bud).
• Branches develop from lateral buds called
axillary buds, which grow at the upper angle
between leaves and the stem.
• In most plants, the apical bud is dominant
over the axillary buds. This phenomenon is
called apical dominance.
Principles of Biology
Plant Growth and Development
The Role of the Meristem in Plant Growth and
Development
• Most animals show determinate growth and stop growing once they reach a
certain age. Most plants, however, have indeterminate growth and keep
growing their entire lives.
• Plants maintain undifferentiated stem cells in special areas called meristems
for life.
• Apical meristems, located at the tips of roots and shoots, produce cells that
cause the plant to become longer.
• Stem cells in lateral meristems produce cells that thicken a plant.
Principles of Biology
The Meristem and Primary Growth
• The main location of all growth in
the stem is found at the meristems,
which are the tissues of the stem
capable of cell division. There are
two types of meristem in the plant
stem: apical meristem, which is
found at the tip of the stem, and
lateral meristem, which is found
surrounding the stem.
• The growth at the apical meristem
that we will now look at is
considered primary growth. This
type of growth increases the length
of the stem, making the plant taller.
It happens in both monocot and
dicot plants.
Plant Growth and Development
Figure 1 Meristems.
Plants maintain several regions
with undifferentiated cells that can
divide and produce cells to build
stems and leaves.
Root apical meristems extend the
roots to allow greater soil, water,
and nutrient access. Shoot apical
meristems produce the primary
plant tissues and body. Axillary
meristems can produce branches;
they are often activated when an
apical meristem has been removed
or damaged.
Principles of Biology
Plant Growth and Development
Primary Growth in Plants
• Primary growth: growth coming from the activity of the apical
meristem.
Primary growth is lengthening growth.
• The apical meristem also makes roots by producing a series of elongated cells behind a
group of tough cells called the root cap.
• Allows stems and leaves to access more sunlight and permits roots to spread through the
soil to access water and minerals.
Principles of Biology
Plant Growth and Development
Primary growth takes place in the root.
•A growing root has three distinct regions:
•The zone of cell division occurs at the apical meristem
where new root cells grow in multiple directions.
•In the zone of elongation, located just behind the root tip,
root cells elongate and force the root tip into new areas
of soil.
•In the zone of differentiation, cells differentiate to produce
the three fundamental tissue systems found in roots and
shoots: dermal tissue, ground tissue, and vascular tissue.
Principles of Biology
Plant Growth and Development
Figure 2 Plant root micrograph.
The different areas of root cell
growth are visible in this
micrograph of a plant root
(Arabidopsis thaliana).
The root is stained blue to
indicate collagen-rich areas of
the root, and highlight cells.
(Arrowheads indicate nuclei. C,
cortex; En, endodermis; Ep,
epidermis; RC, root cap. Scale
bar = 100 um).
Principles of Biology
Plant Growth and Development
Primary growth takes place in the root.
•Roots that branch from other roots are called lateral roots.
•Form from a tissue layer called the pericycle, a thin layer of
meristematic cells within the roots located between the
vascular cylinder and the cortex.
•As they continue to grow, they reach the epidermis, rupture
it, and enter the soil.
Principles of Biology
Plant Growth and Development
Figure 4 Lateral roots grow outwards from the central tissues of a primary root.
Lateral roots begin growing
from the internal pericycle of a
primary root. The pericycle
bulges into the lateral root
tissue as it grows.
The primordial lateral root
continually expands toward the
epidermis of the primary root.
Eventually, the lateral root
breaks through the epidermis of
the primary root and enters the
soil.
Principles of Biology
Plant Growth and Development
Primary growth occurs in the shoots,
which includes the growth of stems and
leaves.
The apical meristem produces dermal, ground, and
vascular meristems that make the cells for all the
tissues of the stem, similar to the root.
Principles of Biology
Plant Growth and Development
Figure 6 Stem tissues.
Like all plant parts,
stems have three
types of tissues.
Compare the different
arrangements of
tissues in dicots and
monocots.
Principles of Biology