2. OUTLINE:
I. A Brief Definition of Roots
II. Perspective: evolution of the root
III. Gross morphology (Tap Root and Fibrous Root)
IV. Apical meristems
V. Primary Structures
A. Primary tissues and tissue regions
• Epidermis
• Cortex
• Endodermis
• Pericycle
• Vascular System
B. Development of primary tissues
3. VI. Development of Lateral Roots
VII. Development of Adventitious Roots
VIII. Root Morphogenesis
IX. Secondary Structure
A. Initiation and Activity of Vascular Cambium
B. Initiation and Activity of Cork Cambium
C. Cambial Activity in Storage Roots
(Anomalous Roots)
X. Modified Roots
A. Contractile Roots
B. Mycorrhiza
C. Root Nodules
•Nitrogen fixation in root nodules
D. Other Modified Roots
4. XI. Lateral transport of water and minerals in the
young root
XII. Types of Roots and Specialized Roots
XIII. Application of Roots
5. ROOT “the hidden half”
constitutes the underground part of the plant
axis
organ of a plant that typically lies below the
surface of the soil
9. Two categories:
TAP ROOT SYSTEM
common in
dicotyledons
a vertical oriented
single large main root
with small lateral
roots
10. develops from a
meristem of the lower
end of the hypocotyl
of the embryo
11. FIBROUS ROOT SYSTEM
common in
monocotyledons
roots in a system that
is made up of many
threadlike members
of more or less equal
length
12.
13. APICAL MERISTEM
Pteridophytes – single apical initial
Lycophytes – small cluster of apical initials
Monocotyledons – having three tiers of initials
17. The quiescent center and its
role in development
Ponce et. al.
described quiescent center as “an architectural
template in the root apical meristem of all
angiosperms and gymnosperm root tips” (which
with surrounding initials)
May regulate the positional and structural
expression of …genes ( which control the
differentiation of tissue region in roots)
18.
19. TISSUES OF A ROOT
Root tissues can be regarded as a series of
concentric rings of different tissues
20. EPIDERMIS
• Single layer of cells
on the exterior of
the root
• NOT covered with
a cuticle
root is designed
for water uptake
cuticle is a
barrier
to water
21. VELAMEN
composed of
compactly arranged
non-living cells
bearing secondary
wall thickenings
primary role as
mechanical
protection and
reduction in loss of
water from the cortex
PNEUMATODES
present in velamen
cells have spiral
thickenings
help in gaseous
exchange
22. Cell type found in epidermis
ROOT HAIRS
developed from the
epidermal cells away
from the root tip
increasing the surface
area available for
water and mineral
absorption
23. CORTEX
• comprised of large
undifferentiated
cells (band of
parenchyma cells)
• functions in the
storage of food
reserves (proteins
and starches) in
root tissues
24. ENDODERMIS
• regulate the uptake
of water and nutrients
into the plant
• spaces between the
cells are covered with
a waxy layer, called
suberin
Similar to grout
between ceramic
tiles, and serves a
similar function
Epidermis
Cortex
Endodermis
Pericycle
Vascular
System
Phloem
Cambium
Xylem
25. Cell type found in endodermis
CASPARIAN STRIP
prevents water
and solutes from
passing between
cells into vascular
cylinder
transports proteins
and controls the
flow
26. In plant anatomy, the Casparian strip is a band of cell wall
material deposited on the radial and transverse walls of the
endodermis, and is chemically different from the rest of the
cell wall, being made of suberin and lignin. It blocks the
passive flow of materials such as water and solutes into the
stele of a plant. The band was first recognized as a wall
structure by Robert Caspary (1818–1887).
27. PERICYCLE
• a thin layer of
undifferentiated
cells (parenchyma
cells)
• a meristem tissue
• the source of new
lateral or
secondary roots
• surrounds the
vascular bundles
28. Vascular tissue
the transport system
Phloem
living cells comprised of seive tube
elements and companion cells
Cambium
a meristematic tissue supplying cells
that will develop into vascular
structures
29. Xylem
dead cells with thickened cell walls,
typically larger than phloem cells
functions in the transport of water and
mineral nutrients
30.
31.
32.
33. PITH
a very small area in the center
(parenchymatous cells with
intercellular space)
34. Root Morphogenesis: The root
apex
The part of the root where growth and
development starts.
Close to the tip is where the production of
new cells and the elongation of the recently-
made cells take place. Such growth in cell
length and cell numbers is how roots can
make their way towards the soil and search
for untapped water and minerals. The
expanded network of roots can also provide
anchorage for the plant.
35.
36.
37.
38.
39.
40.
41.
42. Primary Development of the
Root Tip Region of cell division
~1 mm in length.
Apical meristem
Region of cell elongation
~2 mm in length.
Cells elongate, functional
xylem starts to develop and
phloem is mature
Region of maturation
~2 mm in length.
Root hairs are
produced, functional xylem
and phloem are present.
50. Adventitious roots
the roots developing from any part other than
the radicle.
they cover those roots that develop from stems
(both aerial and underground) and their
branches, from leaves, from large roots and from
the hypocotyls of young plants.
the adventitious roots have a deep seated origin.
they are found in the cortical tissue of bonds and
hypocotyls, stem pericycle, ray parenchyma
between pericycle and cambium, non-
differentiated secondary phloem and cambium
between the vascular bundles, interfascicular
cambium and pericycle or the stem pith,
parenchymatous regions in secondary xylem
formed due to the presence of leaf gaps or
tissues of leaf margins and petioles.
51. Adventitious roots
are most easily
seen in an
epiphytic orchid.
Though these stems
are more upright,
they are
modifications of
creeping rhizomes.
52. Root Penetration
Root depth and distance
depend on soil:
Moisture
Temperature
Composition
Feeder Roots- those
involved in uptake of
water and minerals,
occur usually in the
upper 1 meter of the
soil.
54. Adventitious roots
If primary root stops growing early on and
new roots grow from the stem, it is a Fibrous
Root System
They commonly occur in monocots and
pteridophytes, but also in dicot
Growth of radicle is usually arrested at an
early stage and is replaced by numerous
root that develop from the stem.
55.
56.
57. Tap Root
If primary root becomes the
main root
A persistent taproot system
forms when the radicle keeps
growing and smaller lateral roots
form along the taproot.
58.
59. The shape of taproots can vary
but the typical shapes include:
Conical root: this type of root tuber is conical in
shape, i.e. widest at the top and tapering steadily
towards the bottom.
e.g. carrot
Fusiform root: this root is widest in the middle and
tapers towards the top and the bottom.
e.g. radish
Napiform root: the root has a top-like
appearance. It is very broad at the top and tapers
suddenly like a tail at the bottom.
e.g. Turnips
62. Aerating roots (or knee root or
knee or pneumatophores or
Cypress knee):
Roots rising above the ground,
especially above water such as
in some mangrove genera
(Avicennia, Sonneratia)
the erect roots have a large
number of breathing pores
for exchange of gases.
63. Aerial Root
roots entirely above the ground
Many aerial roots, are used to receive
water and nutrient intake directly from the
air - from fogs, dew or humidity in the air.
Epiphytes - plants living above the surface
on other plants, aerial roots serve for
reaching to water sources or reaching the
surface, and then functioning as regular
surface roots.
64. Contractile roots:
they pull bulbs or corms
of monocots deeper in
the soil through
expanding radially
and contracting
longitudinally
they have a wrinkled
surface
help to pull the plant
deeper
into the soil
65.
66. Coarse Root
Roots that have undergone
secondary thickening and
have a woody structure.
These roots have some ability
to absorb water and
nutrients
main function transport and
to provide a structure to
connect the smaller
diameter,
fine roots to the rest of
the plant.
67. Fine Roots
Primary roots usually
<2 mm diameter that
have the function of
waterand nutrient
uptake.
They are often heavily
branched
and support mycorrhizas.
These roots may be short
lived, but are replaced
by the plant in an
ongoing
process of root 'turnover'.
68. Storage Roots
these roots are modified for storage of
food or water, such as carrots and beets.
They include some taproots and tuberous
roots.
69. Stilt Roots these are adventitious support
roots, common among
mangroves. They grow down
from lateral branches, branching
in the soil.
70. Structural Roots
large roots that have
undergone
considerable
secondary thickening
and provide
mechanical support
to woody plants and
trees.
71. Haustorial Roots
roots of parasitic plants that can absorb water and
nutrients from another plant, such as in mistletoe
(Viscum album) and dodder.
