ROOTS

GROUP 3

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

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

XI. Lateral transport of water and minerals in the

young root

XII. Types of Roots and Specialized Roots

XIII. Application of Roots

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

I. Perspective: Evolution of the root

First Vascular Plant

Rhyniophytes

Trimerophytes

Progymnosperms

Seed plants

Lycophytes

Spenophytes

Ferns

Anchorage

Absorption

Transport of

minerals and water

Storage of

photosynthate

Rhaphanus sativus (radish)

Arabidopsis thaliana

Two categories:

TAP ROOT SYSTEM

common in

dicotyledons

a vertical oriented

single large main root

with small lateral

roots

develops from a

meristem of the lower

end of the hypocotyl

of the embryo

FIBROUS ROOT SYSTEM

common in

monocotyledons

roots in a system that

is made up of many

threadlike members

of more or less equal

length

APICAL MERISTEM

Pteridophytes – single apical initial

Lycophytes – small cluster of apical initials

Monocotyledons – having three tiers of initials

MONOCOTYLEDON

DICOTYLEDON

CLOWES 1959 Hanstein 19th century

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)

TISSUES OF A ROOT

Root tissues can be regarded as a series of

concentric rings of different tissues

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

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

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

CORTEX

• comprised of large

undifferentiated

cells (band of

parenchyma cells)

• functions in the

storage of food

reserves (proteins

and starches) in

root tissues

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

Cell type found in endodermis

CASPARIAN STRIP

prevents water

and solutes from

passing between

cells into vascular

cylinder

transports proteins

and controls the

flow

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).

PERICYCLE

• a thin layer of

undifferentiated

cells (parenchyma

cells)

• a meristem tissue

• the source of new

lateral or

secondary roots

• surrounds the

vascular bundles

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

Xylem

dead cells with thickened cell walls,

typically larger than phloem cells

functions in the transport of water and

mineral nutrients

PITH

a very small area in the center

(parenchymatous cells with

intercellular space)

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.

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.

Development of Lateral Roots

A, B – Stele

C, D – Endodermis

E, F –

Endodermis/Stele

Development of

Adventitious Roots

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, interfascicularcambium 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.

Adventitious roots

are most easily

seen in an

epiphytic orchid.

Though these stems

are more upright,

they are

modifications of

creeping rhizomes.

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.

Types of Roots

and

Specialized

Roots

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.

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.

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

Fibrous vs. Taproot

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.

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.

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

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.

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'.

Storage Roots

these roots are modified for storage of

food or water, such as carrots and beets.

They include some taproots and tuberous

roots.

Stilt Roots these are adventitious support roots, common among mangroves. They grow down from lateral branches, branching in the soil.

Structural Roots

large roots that have

undergone

considerable

secondary thickening

and provide

mechanical support

to woody plants and

trees.

Haustorial Roots roots of parasitic plants that can absorb water and

nutrients from another plant, such as in mistletoe

(Viscum album) and dodder.

APPLICATION

Of ROOTS

Anchorage and support

Absorption and conduction

Storage

Photosynthesis

Aeration

Movement

Reproduction