Roots

ROOTS

Professor Joan S. Awingan

Functions:

1. Anchorage – to locate water and minerals, roots permeate the soil. In doing so, they anchor the plant in one place for its entire life.

2. Absorption – roots absorb large amounts of water and dissolved minerals (nitrates, phosphates, and sulfates) from the soil.

Functions:

3. Conduction - water and minerals upward into the stem and food from leaves to storage regions of roots

4. Storage – roots store large amounts of energy reserves, initially produced in the leaves of plants via photosynthesis, and transported in the phloem, as sugar, to the roots for storage, usually as sugar or starch, until they are needed.

5.Reproduction

6.Photosynthesis

What are the primary functions of roots?

Embryonic root or radicle

The first root that comes from a plant is called the radicle

Root System - the entire mass of underground roots produced by a

plant

MAJOR KINDS OF ROOT SYSTEM

1. Taproot system – a strongly developed main root which grows downwards bearing lateral roots much smaller than itself.– In most dicots, the radicle enlarges to form a prominent taproot

that persists throughout the life of the plant.– Many progressively smaller branch roots grow from the taproot.– This system is called a taproot system; common in dicots and

conifers.– In plants such as carrots and sugar beets, fleshy taproots store

large reserves of food, usu. as carbohydrates.– Taproots are modified for reaching deep water in the ground:

e.g. the long taproots of poison ivy (Rhus toxicodendron), dandelion (Taraxacum sp.) and mesquite (Prosopis sp.).

2.Fibrous (diffuse) root system – has several to many roots of the same size that develop from the end of the stem, with smaller lateral roots branching off of them. a. Most monocots (including grasses and onions) have a fibrous root system.b. In these plants, the radicle is short-lived and is replaced by a mass of adventitious roots (from the Latin, adventicius, meaning “not belonging to”), which are roots that form on organs other than roots. Because these roots arise not from preexisting roots, but from the stem, they are said to be adventitious.c. The adventitious roots of monocots are very extensive and cling tenaciously to soil particles. These plants are excellent for preventing erosion.d. The fibrous root of a few plants are edible – sweet potatoes (Ipomoea batatas) are the fleshy part of a fibrous root system.

Tap root and Fibrous (Diffuse) Root Systems – Both arise from radicle

Adventitious roots – roots that develop in an unusual place. There are several types of adventitious roots besides those of monocots.a. Adventitious roots are common along rhizomes (underground stems) of ferns, club mosses (Lycopodium), and horsetail (Equisetum).b. In some plants, adventitious roots are a primary means of vegetative reproduction: forests of quaking aspen (Populus tremuloides) are often a single clone spread by adventitious roots. Prop roots of mangrove (Rhizophora sp.) are like stilt roots, an adventitious root that grows out from the lower part of a stem into the soil to support the stem, or grows down from a lower branch in to the soil to support that branch (strangler figs).c. You might see adventitious roots of ivy (Hedera helix) growing along the stem as it climbs along a fence or into a tree.Ex: strawberry

TAKE HOME POINT :

MOST DICOTS HAVE A TAPROOT SYSTEM CONSISTING OF A LARGE TAPROOT AND SMALLER BRANCH ROOTS. TAPROOT SYSTEMS MAXIMIZE SUPPORT AND STORAGE.

MONOCOTS HAVE A FIBROUS ROOT SYSTEM CONSISTING OF SIMILARLY SIZED ROOTS THAT MAXIMIZE ABSORPTION.

ADVENTITIOUS ROOTS ARE ROOTS THAT FORM ON ORGANS OTHER THAN ROOTS.

Adventitious Roots: roots that arise from anything other than the radicle

Adventitious Roots: roots that arise from anything other than the radicle

SPECIALIZED ROOTS

1. Storage – thickened roots which contain large amount of stored food (starch or carbohydrates)

or sometimes water to survive cold or dry seasons

Fusiform roots : These root are thicker in the middle and tapered on both ends. In this type of roots both hypocotyl and root help in storage of food.

ex: Radish. Conical roots : These roots are thicker at their upper side

and tapering at basal end.ex: Carrot.

Napiform : These roots become swollen and spherical at upper end and tapered like a thread at their lower end. ex: Turnip

2. Reproduction/Propagation – formation of adventitious roots, that is, roots that develop in an unusual place

ex: sweet potato, pandan

3. Gas Exchange/Aeration – presence of pneumatophores (erect root that rises up above the soil or water and promotes gas exchange). Internally, they are filled with a specialized parenchyma called aerenchyma. Externally, they have numerous pores or lenticels over their surface. Common in plants that grow in water-logged soils ex: mangrove, cypress

Cypress Knees

4. Photosynthesis – can perform photosynthesis, usually with green aerial roots (with chloroplasts)

ex: epiphytic orchids

5. Support –

a. Buttress roots – big roots that look like they arise from the base of the tree trunk provide additional tensile

forces to resist uprooting of large tropical trees. Ex: fig

Buttress Roots

b. Prop / stilt roots – Large pillars like roots develop from horizontally spread branches of tree. They grow vertically downward into the soil and support the spreading branches. The main function is mechanical support or pillars

Ex: corn, pandan, banyan

c. Climbing / clinging roots – these roots arising from nodes attach hemselves to some support and

climb over it; ex: ivy

d. Brace roots - arise from the main stem. These penetrate obliquely down in to the soil and give

support to the plant ex: corn, sugarcane, pandan

6. Parasitic roots

Haustorial roots are adventitious parasitic roots usually common in flowering plants called haustoria . They

penetrate the tissues of the host and connect to the vascular system, thus becoming part of the host pipelines. Parasitic roots lack most of the tissues of ordinary roots.

Ex: dodder and mistletoe

Parasitic roots - Dodder

7. Mutualistic roots

Mycorrhizal roots are known from 90 percent of plant species and are a mutualistic association of a fungus with plant root tissue.

Most plants require specific mycorrhizal fungi without which they are unable to absorb sufficient quantities of P, Zn, and Mn.

The fungus takes the place of root hairs and may penetrate the cortex completely ( endomycorrhizae) or remain on the surface of the root (ectomycorrhizae).

• Mycorrhizae or "fungus roots" where a symbiotic relationship forms between a plant and a fungus.

• In this partnership the fungus provides protection against some types of pathogens and increase the surface area for the absorption of essential nutrients (e.g. phosphorous) from the soil. The plant in return provides food for the fungus in the form of sugar and amino acids

There are also associations between bacteria and roots of certain plants.

Nodules – spherical structures at the roots of leguminous plants (e.g. peas), where nitrogen-fixing

bacteria live. These bacteria convert the atmospheric nitrogen into a form that can be used by plants