Transcript CB098-008.41_Roots - Workforce Solutions

The Root
System
The Functions of Roots
- Absorption of water and nutrients (dissolved
salts & minerals).
- Conduction of absorbed materials
into the plant body.
- Anchorage of plant in soil.
- Food storage (Carrots and Beets).
- Many roots have relationships with bacteria and
fungi in the soil in the rhizosphere (contact
zone between soil and root surface, often a few
millimeters thick).
In the plant embryo, the radicle is the first root
that is initiated.
The Root System
and Shoot System
support each other.
Types of Root Systems
Fibrous Root System
- Several main roots branch to
form a dense mass of roots, which
holds the plant firmly in place. As
a result, grasses make fine ground
cover because they minimize soil
erosion. Basically, no common
single primary root. Examples:
Many monocots, Corn, Rye, Many
Grasses, Small Garden Plants.
Tap Root System
- Posses one main root or primary root (Tap Root) from which lateral
roots branch. Some taproots tap water deep in the soil. Tap Root
Systems often have a large storage root (carrot, turnips and beets).
Other Examples: Some desert plants, Hickory, Milkweed, Many
Dicots, Dandelion.
In your yard, how can dandelions and grass not compete for water?
Plants Have Different Types of Roots
When seeds germinate, the embryonic root (Radicle) begins.
In a tap root
system, the
radicle forms the
primary root
then adds lateral
roots (Branch
Roots).
Example: Pea.
In a fibrous root
system, a single
radicle forms but
in addition
several other
embryonic roots
(seminal roots)
form just above
the radicle. All
roots then
branch and from
a fibrous root
system.
Example: Wheat.
Types of Adventitious Roots
Adventitious roots originate on leaves and stems. These are
often roots that arise above ground.
Seminal Roots - Adventitious roots forming
at the base of the seedling stem. Seminal
roots are adventitious because they don’t
emerge from another root.
Prop Roots – In a young corn plant, soon
after germination prop roots develop on the
stem just above the soil. Prop roots
support the plant and absorb water and
minerals.
Aerial Roots – These roots are exposed to
air, they extend down from branches into
the soil. They hold up branches of a tree
and absorb water and nutrients. In English
Ivy, aerial roots enable the ivy to cling to
the sides of buildings.
CORN
Types
of
Adventitious
Roots
Pneumatophores - Aerial
roots that stick up out of the
water and serve to aerate
the root cells. These are
common in trees that grow
in swamps or salt marches
like mangroves.
Root
Propagation
can often occur
with cut stems
of some plants.
Roots will grow
off the stem.
These roots are
adventitious.
The Development of Roots
Root Cap covers the
end of the root tip
for protection. It is
the site of gravity
perception & it
controls the
direction of root
growth.
Root tip is organized into 3 regions:
1) Root Apical Meristem (RAM) - Derives the
cells and tissues of the root.
2) Region of Elongation - Cells are
elongating in the roots.
3) Region of Maturation - Basal (Further Up)
to the region of elongation where root
hairs form and cells reach maturity.
The Development of Roots
Primary Tissues
Below Primary Meristems
give rise to the above
primary tissues.
Primary Meristems
RAM gives rise to above
primary meristems.
The Development of Roots
Primary
Meristems
Primary
Tissues
Some epidermal cells have
root hairs.
Parenchyma, Endodermis
and Casparian strip.
These tissues are within
the vascular cylinder.
Buttercup Root (Cross Section)
Root Diagram (Cross Section)
The Structure of Roots
The Epidermis covers the entire root surface and is modified for absorption
(Root hairs on epidermal cells help this).
The Cortex cells (parenchyma) have many plastids for the storage of starch.
The Vascular Cylinder (stele) consists of vascular tissues (xylem and phloem)
surrounded by one
or more layers of
tissue called the
pericycle.
The Pericycle gives rise
to lateral roots and
contributes to the
formation of the
secondary
meristems.
The Endodermis is
tightly packed layer
of cells surrounding
the vascular
Dicot Root
cylinder.
Cross Section
Endodermis
Each endodermis cell is wrapped with Casparian Strip, a
continuous band of suberin, a waxy material that is impervious to
water and dissolved minerals The function of the endodermis is
to select what minerals enter the vascular cylinder and the body
of the plant.
Control of water and nutrient movement into the xylem is a
function of the endodermis.
Some Roots Have Special Functions
Haustorial Root – Modified root of certain parasitic plants, such as dodder,
penetrates into the host plant.
Root Nodule is a knot (swelling) on a root,
caused by the infection of Nitrogen-fixing bacteria
(N2 gas into NH4+) named Rhizobium sp. Plants
benefit by receiving nitrogen in the correct form
and bacteria receive housing and nutrients from
the plant.
Bacteria enter the plant by passing through a tiny
infection thread that penetrates the root hairs.
Once inside the host, the bacteria penetrate the
cortex of the root forming a swollen mass (nodule)
of cells filled with bacteria.
Some Roots Have Special Functions
Mycorrhiza (plural, mycorrhizae) – a symbiotic association between a fungus and
a root of a plant. These are short, forked root structures common to as many as 90% of
seed plants. This relationship makes roots more efficient in mineral absorption. Fungi
receive housing and carbohydrates from the plant. Mycorrhizae are not always essential
but the fungus can help the plant fight disease.
2 Main Types of Mycorrhizae
Ectotrophic – fungal cells do NOT
Endotrophic – fungal cells actually enter the
penetrate plant root cells. However, it
does form a sheath or mantle over the
entire root.
cortex cells of the plant.
BIO 141 Botany with Laboratory
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