Roots Chapter 5 Copyright © McGraw-Hill Companies Permission Required for Reproduction or Display Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies

Outline Root Function Root Development Root Structure Specialized Roots Mycorrhizae Root Nodules Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies

There are several functions for a root Anchorage Water and mineral absorption/conduction Storage Starch Water Extensive underground organ A single grass plant 15 x 106 roots = 400 miles of root / 2 ft3 soil Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies

Stern - Introductory Plant Biology: 9th Ed Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw 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: 9th Ed. - All Rights Reserved - McGraw Hill Companies

Root development Radicle Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies

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

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

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

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

ROOTS Root Function Root Development Root Structure Specialized Roots Mycorrhizae Root Nodules Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies

Region of Cell Division Region of Cell Elongation Root Structure 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: 9th Ed. - All Rights Reserved - McGraw Hill Companies

Root Structure and Root Tissue Comparison Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies

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

Region of Cell Division Root apical meristem 12 to 36 h cell cycle Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies

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

Region of Maturation Sometimes called “region of differentiation” or “root-hair zone” Most cells differentiate into various distinctive cell types. Vascularization and development of root hairs Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw 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 2ft3 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: 9th Ed. - All Rights Reserved - McGraw Hill Companies

Region of MaturationCortex cells Cortex cells mostly store food Between epidermis and inner tissues. Has endodermis as inner boundary (single layer cells) Cell walls impregnated with suberin bands; Casparian Strips. 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: 9th Ed. - All Rights Reserved - McGraw Hill Companies

Region of MaturationCortex cells Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies

Region of Maturation Vascular Cylinder lies at the inside of the endodermis. (xylem/phloem) Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies

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

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

Specialized Roots Food Storage Roots Sweet Potatoes Yams Store starch, carbohydrates Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies

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

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

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

Specialized Roots Aerial Roots-can absorb water from the air; has a thick epidermis to reduce water loss Orchids Banyan trees www.hcs.ohio-state.edu/ hcs300/anat1.htm Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies

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

Mycorrhizaefungi Mycorrhizae form a mutualistic association with plant roots. (found in3/4 of all seed plants) Fungus is able to absorb and concentrate phosphorus much better than it can be absorbed by the root hairs. Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw 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/BOT135/Lect26.htm Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies

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

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

Review Root Development Root Structure Specialized Roots Mycorrhizae Root Nodules Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies