Roots Chapter 5 Copyright Mc GrawHill Companies Permission

Outline • • • Root Function Root Development Root Structure Specialized Roots Mycorrhizae Root

Function • • There are several functions for a root v Anchorage v Water

Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc.

How Roots Develop • When a seed germinates, the embryo’s radicle grows out and

Root development Radicle Stern - Introductory Plant Biology: 9 th Ed. - All Rights

Development: Tap root -- Fibrous root • • May develop into thick taproot with

Adventitious Roots Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved

What are the advantages and disadvantages of a fibrous and a taproot system? Advantages

Disadvantages • • Fibrous v Does not reach water and nutrients deep in soil

ROOTS • • • Root Function Root Development Root Structure Specialized Roots Mycorrhizae Root

Root Structure 1. 2. 3. 4. • • Root Cap Region of Cell Division

Root Structure and Root Tissue Comparison Stern - Introductory Plant Biology: 9 th Ed.

Root Structure • Root Cap - Thimble-shaped mass of parenchyma cells covering each root

Region of Cell Division • Root apical meristem • 12 to 36 h cell

Region of Elongation • • About 1 cm from root tip Cells become several

Region of Maturation • • • Sometimes called “region of differentiation” or “roothair zone”

Region of maturation Root hairs Tuberous extensions of specialized epidermal cells • • Absorb

Region of Maturation Cortex cells • • Cortex cells mostly store food Between epidermis

Region of Maturation Cortex cells Stern - Introductory Plant Biology: 9 th Ed. -

Region of Maturation • Vascular Cylinder lies at the inside of the endodermis. (xylem/phloem)

Development of Secondary Roots • Pericycle lies directly against the inner boundary of the

What structure within the root is responsible forming secondary or lateral roots? • •

Specialized Roots • Food Storage Roots v Sweet Potatoes v Yams • Store starch,

Specialized Roots • Carrots, beets, turnips, radishes are foodstorage tissues that are a combination

Specialized Roots • • Manroot (Marah) Water Storage Roots v Pumpkin Family Propagative Roots

Specialized Roots • Pneumatophores v Spongy roots that extend above the water’s surface and

Specialized Roots • Aerial Roots-can absorb water from the air; has a thick epidermis

Specialized Roots • • Contractile Roots v Pull plant deeper into the soil. -

Mycorrhizae fungi • Mycorrhizae form a mutualistic association with plant roots. (found in 3/4

Mycorrhizae fungi Two Hibiscus plants. Left plant without Mycorrhizae, right with Mycorrhizae. Mucorrhizal arbuscule

Root Nodules • Few species of bacteria (Rhizobium) produce enzymes that can convert nitrogen

Root Nodules Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved

Review • • • Root Development Root Structure Specialized Roots Mycorrhizae Root Nodules Stern

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Function • • There are several functions for a root v Anchorage v Water and mineral absorption/conduction v Storage - Starch - Water Extensive underground organ v A single grass plant 6 3 - 15 x 10 roots = 400 miles of root / 2 ft soil Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

How Roots Develop • When a seed germinates, the embryo’s radicle grows out and develops into the first root. Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Development: Tap root -- Fibrous root • • May develop into thick taproot with branch roots. v Dicotyledonous Plants May develop a fibrous root system. v Monocotyledonous Plants Adventitious roots are roots that develop from non-root plant parts Both monocots and dicots Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

What are the advantages and disadvantages of a fibrous and a taproot system? Advantages • • Fibrous v Large surface area, increased access to water and minerals Taproot v Good for a storage of nutrients, can access water and nutrients at great depths, good during drought periods Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Disadvantages • • Fibrous v Does not reach water and nutrients deep in soil profile - not good during drought v Not good for storage of water or carbohydrates Taproot v Not as efficient as fibrous at getting water & minerals in upper soil profile. Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Root Structure 1. 2. 3. 4. • • Root Cap Region of Cell Division Region of Cell Elongation Region of Cell Maturation Not all regions well-defined at their boundaries. Development in roots unlike other organs follows a linear vector Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Root Structure • Root Cap - Thimble-shaped mass of parenchyma cells covering each root tip. v Protects tissue from damage. v Function in gravity perception. v Cells secrete a slimy substance and slough off forming a slimy lubricant that helps roots move through soil Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Region of Elongation • • About 1 cm from root tip Cells become several times their original length. v Vacuoles merge and form 90% of the mature cell Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Region of Maturation • • • Sometimes called “region of differentiation” or “roothair zone” Most cells differentiate into various distinctive cell types. Vascularization and development of root hairs Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Region of maturation Root hairs Tuberous extensions of specialized epidermal cells • • Absorb water and minerals and adhere tightly to soil particles. Grass plant 2 ft 3 soil, 15 x 106 roots has 14 x 109 root hairs - • Root surface area ~ volleyball court Root hair surface area ~ football field Root hairs function for 2 days to 3 weeks Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Region of Maturation Cortex cells • • Cortex cells mostly store food Between epidermis and inner tissues. v Has endodermis as inner boundary (single layer cells) - Cell walls impregnated with suberin bands; Casparian Strips. Ø Forces all water and dissolved substances entering and leaving the central core to pass through plasma membranes of the endodermal cells. Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Development of Secondary Roots • Pericycle lies directly against the inner boundary of the endodermis. v Lateral (branch) Roots develop Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

What structure within the root is responsible forming secondary or lateral roots? • • • A. Casparian strip B. Vascular cambium C. Cork cambium D. Pericycle E. Endodermis Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Specialized Roots • Carrots, beets, turnips, radishes are foodstorage tissues that are a combination of root and stem Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Specialized Roots • • Manroot (Marah) Water Storage Roots v Pumpkin Family Propagative Roots v Adventitious Buds develop into suckers. - Fruit Trees Sisal Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Specialized Roots • Pneumatophores v Spongy roots that extend above the water’s surface and enhance gas exchange between the atmosphere and subsurface roots. Mangroves Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Specialized Roots • Aerial Roots-can absorb water from the air; has a thick epidermis to reduce water loss v Orchids v Banyan trees www. hcs. ohio-state. edu/ hcs 300/anat 1. htm Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Specialized Roots • • Contractile Roots v Pull plant deeper into the soil. - Lilly Bulbs. Buttress Roots v Stability - Tropical Trees. Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Mycorrhizae fungi • Mycorrhizae form a mutualistic association with plant roots. (found in 3/4 of all seed plants) v Fungus is able to absorb and concentrate phosphorus much better than it can be absorbed by the root hairs. Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Mycorrhizae fungi Two Hibiscus plants. Left plant without Mycorrhizae, right with Mycorrhizae. Mucorrhizal arbuscule inside a plant cell www. botany. hawaii. edu/faculty/ wong/BOT 135/Lect 26. htm Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies

Root Nodules • Few species of bacteria (Rhizobium) produce enzymes that can convert nitrogen into nitrates and other nitrogenous substances readily absorbed by roots. v Legume Family (Fabaceae) - Root nodules contain large numbers of nitrogen-fixing bacteria. Stern - Introductory Plant Biology: 9 th Ed. - All Rights Reserved - Mc. Graw Hill Companies