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Roots Chapter 5 Copyright © McGraw-Hill Companies Permission

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1 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

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

3 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

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

5 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

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

7 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

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

9 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

10 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

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

12 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

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

14 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

15 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

16 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

17 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

18 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

19 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

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

21 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

22 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

23 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

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

25 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

26 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

27 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

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

29 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

30 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

31 Mycorrhizaefungi Two Hibiscus plants. Left plant without Mycorrhizae, right with Mycorrhizae. Mucorrhizal arbuscule inside a plant cell wong/BOT135/Lect26.htm Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies

32 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

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

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

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