Plant Roots Structure and Function

Author: Mike DanaRevised by: Geonyzl Alviola

Reference:http://www.hort.purdue.edu/hort/courses/HORT101Spring/Roots/index.htm

Objectives of today’s lecture:

• Learn about the functions of the root system and its importance to plant growth and development

• Learn the structures that allow the root to perform these functions

• Learn some of the modifications that occur in roots

Functions of the Root

• anchorage to the soil (or other substrate)

• absorption of water

• acquisition of mineral nutrients

• a tissue for energy (food) storage

• for propagation and dispersal of some species

Functions of the Root

Root morphology is highly variable

• most dicotyledonous plants (those with 2 seed leaves) have a prominent primary root

• monocots (with one cotyledon or seed leaf) typically have a more diffuse fibrous root system

-Roots originated from meristems- Apical meristem produces the cap - Cell divisions at the apical meristem cause the root to lengthen- Farther up, cells differentiate and mature

- developed from the epidermal cells away from the root tip

- Increasing the surface area available for water and mineral absorption

Root hairs

Root hairs

• Root hairs contribute the largest fraction of root surface area

• In the winter rye example given earlier, more than 4,000 sq. ft. of the 6,500 sq. ft. of root surface area comes from root hairs

• Epidermis functions in the uptake of water and minerals

• Large surface area facilitates uptake

Tissues of the root

EpidermisCortexEndodermis

PericycleVascularSystem

Phloem

Cambium

Xylem

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

Epidermis

Cortex

Endodermis

Pericycle

VascularSystem

Phloem

Cambium

Xylem

• Comprised of large undifferentiated cells

• Functions in the storage of food reserves (proteins and starches) in root tissues

Cortex

Epidermis

Cortex

Endodermis

Pericycle

VascularSystem

Phloem

Cambium

Xylem

Endodermis

• Single layer of cells outside vascular system

• 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

VascularSystem

Phloem

Cambium

Xylem

Endodermis

• Blocks passage of water and dissolved nutrients into the vascular system

• Water, nutrients and other solutes must enter a cell, cannot go round the endodermis

• Endodermis functions to regulate the uptake of water and nutrients into the plant

Pericycle

• A thin layer of undifferentiated cells

• A meristem tissue

• The source of new lateral, or secondary, roots

• Surrounds the vascular bundles

pericycle

pericycle

phloem

xylem

root hair

endodermis

epidermis

cortex

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

Vascular tissue

• Xylem

• dead cells with thickened cell walls, typically larger than phloem cells

• functions in the transport of water and mineral nutrients

A long look at the root

• A longitudinal section through the root (from bottom to top) shows these various tissues and how they develop.

A long look at the root

• Elongation zone

• Where cells elongate and differentiate

• Pushes the root tip through the soil

• Maturation zone

• Cells develop their final form

• Root hairs form, xylem cells thicken and die

A long look at the root

• Root cap

• Cells are sloughed off

• Protects the apical meristem

• Apical meristem

• Source of cells for the root

root apical meristem

root cap

Organ Tissue Cell Type

Root

Epidermis

VascularSystem

Epidermal

Root hairs

Phloem

Cambium

Xylem

Cortex Parenchyma

Endodermis

Pericycle

CasparianStrip

Parenchyma

Root Development

• Radicle – the first root to develop in a vascular plant

• Primary root – the matured root developed from the radicle

• Lateral roots – roots arised from other roots.

• Adventitious roots – root arise from nonroot organ

radicle

Primary root Adventitious root

Root modifications

• The organ that is consumed in many vegetable crops, such as carrot and sweet potato, is a modified root that serves as a storage tissue

• Other modifications for support

Modifications of the root

• Taproot - if the primary root is dominant

• Fibrous root system – if the primary root withers and more are adventitous roots.

Types of Roots

• Storage roots

– mostly biennial plants

- Tap root become thicken

- Stores great amount of starch

• Aerial roots

- These are adventitious roots that don’t enter the soil

- Absorb water and minerals from the air

- Mostly epiphytic plants have this type of roots

Contractile roots

- roots that actually contract vertically

- To pull the stock further into the soil.

- Contractile roots are usually broad, fleshy, vertical, tapering, wrinkled looking and very distinct of the rather cylindrical fine absorbent roots and are capable of incredible effort.

Haworthia emelyae v. comptoniana

Haustoria

• roots of a parasitic plant

• It penetrate the tissue of a host plant

Prop roots

• Grow from the base of the stem

• Serve as to support of the plant with weak stems

pneumatophores

• Roots that grow upwardly from soil to capture oxygen.

• Mostly found in marsh and swampy areas

Buttress roots

• large roots on all sides of a tall or shallowly rooted tree.

• Provide a mechanical support to a tree

The End