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

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Presentation on theme: "Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Roots Chapter 5 Copyright © McGraw-Hill Companies Permission."— Presentation transcript:

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

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

3 Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Function 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 10 6 roots = 400 miles of root / 2 ft 3 soil

4 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.

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

7 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

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

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

10 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.

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

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

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

14 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

15 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

16 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

17 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

18 Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Region of maturation  Root hairs Absorb water and minerals and adhere tightly to soil particles. Grass plant 2ft 3 soil, 15 x 10 6 roots has 14 x 10 9 root hairs - Root surface area ~ volleyball court - Root hair surface area ~ football field Root hairs function for 2 days to 3 weeks Tuberous extensions of specialized epidermal cells

19 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.

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

21 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)

22 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

23 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

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

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

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

27 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

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

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

30 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.

31 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

32 Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw 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.  Legume Family (Fabaceae) - Root nodules contain large numbers of nitrogen-fixing bacteria.

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

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


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