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ROOTS
The document outlines the structure and function of plant roots. It discusses the evolution of roots from early vascular plants. There are two main root systems - taproots which develop from a single main root, and fibrous root systems with many branching roots. Primary root tissues include the epidermis, cortex, endodermis, pericycle and vascular tissues. Root growth and development is driven by the apical meristem. Lateral and adventitious roots develop from root primordia. Roots undergo secondary growth and have specialized structures to carry out functions like storage, support and nutrient absorption.
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ROOTS
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- 2. OUTLINE: I. A BriefDefinition of Roots II. Perspective: evolution of the root III. Gross morphology (Tap Root and Fibrous Root) IV. Apical meristems V. Primary Structures A. Primary tissues and tissue regions • Epidermis • Cortex • Endodermis • Pericycle • Vascular System B. Development of primary tissues
- 3. VI. Development ofLateral Roots VII. Development of Adventitious Roots VIII. Root Morphogenesis IX. Secondary Structure A. Initiation and Activity of Vascular Cambium B. Initiation and Activity of Cork Cambium C. Cambial Activity in Storage Roots (Anomalous Roots) X. Modified Roots A. Contractile Roots B. Mycorrhiza C. Root Nodules •Nitrogen fixation in root nodules D. Other Modified Roots
- 4. XI. Lateral transportof water and minerals in the young root XII. Types of Roots and Specialized Roots XIII. Application of Roots
- 5. ROOT “the hiddenhalf” constitutes the underground part of the plant axis organ of a plant that typically lies below the surface of the soil
- 6. I. Perspective: Evolutionof the root First Vascular Plant
- 7. Rhyniophytes Trimerophytes Progymnosperms Seed plants Lycophytes Spenophytes Ferns Anchorage Absorption Transport of minerals and water Storage of photosynthate
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- 9. Two categories: TAP ROOTSYSTEM common in dicotyledons a vertical oriented single large main root with small lateral roots
- 10. develops froma meristem of the lower end of the hypocotyl of the embryo
- 11. FIBROUS ROOT SYSTEM common in monocotyledons roots in a system that is made up of many threadlike members of more or less equal length
- 13. APICAL MERISTEM Pteridophytes– single apical initial Lycophytes – small cluster of apical initials Monocotyledons – having three tiers of initials
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- 16. CLOWES 1959 Hanstein19th century
- 17. The quiescent centerand its role in development Ponce et. al. described quiescent center as “an architectural template in the root apical meristem of all angiosperms and gymnosperm root tips” (which with surrounding initials) May regulate the positional and structural expression of …genes ( which control the differentiation of tissue region in roots)
- 19. TISSUES OF AROOT Root tissues can be regarded as a series of concentric rings of different tissues
- 20. EPIDERMIS • Single layerof cells on the exterior of the root • NOT covered with a cuticle root is designed for water uptake cuticle is a barrier to water
- 21. VELAMEN composed of compactlyarranged non-living cells bearing secondary wall thickenings primary role as mechanical protection and reduction in loss of water from the cortex PNEUMATODES present in velamen cells have spiral thickenings help in gaseous exchange
- 22. Cell type foundin epidermis ROOT HAIRS developed from the epidermal cells away from the root tip increasing the surface area available for water and mineral absorption
- 23. CORTEX • comprised oflarge undifferentiated cells (band of parenchyma cells) • functions in the storage of food reserves (proteins and starches) in root tissues
- 24. ENDODERMIS • regulate theuptake of water and nutrients into the plant • spaces between the cells are covered with a waxy layer, called suberin Similar to grout between ceramic tiles, and serves a similar function Epidermis Cortex Endodermis Pericycle Vascular System Phloem Cambium Xylem
- 25. Cell type foundin endodermis CASPARIAN STRIP prevents water and solutes from passing between cells into vascular cylinder transports proteins and controls the flow
- 26. In plant anatomy,the Casparian strip is a band of cell wall material deposited on the radial and transverse walls of the endodermis, and is chemically different from the rest of the cell wall, being made of suberin and lignin. It blocks the passive flow of materials such as water and solutes into the stele of a plant. The band was first recognized as a wall structure by Robert Caspary (1818–1887).
- 27. PERICYCLE • a thinlayer of undifferentiated cells (parenchyma cells) • a meristem tissue • the source of new lateral or secondary roots • surrounds the vascular bundles
- 28. Vascular tissue thetransport system Phloem living cells comprised of seive tube elements and companion cells Cambium a meristematic tissue supplying cells that will develop into vascular structures
- 29. Xylem dead cellswith thickened cell walls, typically larger than phloem cells functions in the transport of water and mineral nutrients
- 33. PITH a verysmall area in the center (parenchymatous cells with intercellular space)
- 34. Root Morphogenesis: Theroot apex The part of the root where growth and development starts. Close to the tip is where the production of new cells and the elongation of the recently- made cells take place. Such growth in cell length and cell numbers is how roots can make their way towards the soil and search for untapped water and minerals. The expanded network of roots can also provide anchorage for the plant.
- 42. Primary Development ofthe Root Tip Region of cell division ~1 mm in length. Apical meristem Region of cell elongation ~2 mm in length. Cells elongate, functional xylem starts to develop and phloem is mature Region of maturation ~2 mm in length. Root hairs are produced, functional xylem and phloem are present.
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- 46. A, B –Stele C, D – Endodermis E, F – Endodermis/Stele
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- 50. Adventitious roots the roots developing from any part other than the radicle. they cover those roots that develop from stems (both aerial and underground) and their branches, from leaves, from large roots and from the hypocotyls of young plants. the adventitious roots have a deep seated origin. they are found in the cortical tissue of bonds and hypocotyls, stem pericycle, ray parenchyma between pericycle and cambium, non- differentiated secondary phloem and cambium between the vascular bundles, interfascicular cambium and pericycle or the stem pith, parenchymatous regions in secondary xylem formed due to the presence of leaf gaps or tissues of leaf margins and petioles.
- 51. Adventitious roots aremost easily seen in an epiphytic orchid. Though these stems are more upright, they are modifications of creeping rhizomes.
- 52. Root Penetration Root depthand distance depend on soil: Moisture Temperature Composition Feeder Roots- those involved in uptake of water and minerals, occur usually in the upper 1 meter of the soil.
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- 54. Adventitious roots Ifprimary root stops growing early on and new roots grow from the stem, it is a Fibrous Root System They commonly occur in monocots and pteridophytes, but also in dicot Growth of radicle is usually arrested at an early stage and is replaced by numerous root that develop from the stem.
- 57. Tap Root Ifprimary root becomes the main root A persistent taproot system forms when the radicle keeps growing and smaller lateral roots form along the taproot.
- 59. The shape oftaproots can vary but the typical shapes include: Conical root: this type of root tuber is conical in shape, i.e. widest at the top and tapering steadily towards the bottom. e.g. carrot Fusiform root: this root is widest in the middle and tapers towards the top and the bottom. e.g. radish Napiform root: the root has a top-like appearance. It is very broad at the top and tapers suddenly like a tail at the bottom. e.g. Turnips
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- 62. Aerating roots (orknee root or knee or pneumatophores or Cypress knee): Roots rising above the ground, especially above water such as in some mangrove genera (Avicennia, Sonneratia) the erect roots have a large number of breathing pores for exchange of gases.
- 63. Aerial Root rootsentirely above the ground Many aerial roots, are used to receive water and nutrient intake directly from the air - from fogs, dew or humidity in the air. Epiphytes - plants living above the surface on other plants, aerial roots serve for reaching to water sources or reaching the surface, and then functioning as regular surface roots.
- 64. Contractile roots: theypull bulbs or corms of monocots deeper in the soil through expanding radially and contracting longitudinally they have a wrinkled surface help to pull the plant deeper into the soil
- 66. Coarse Root Rootsthat have undergone secondary thickening and have a woody structure. These roots have some ability to absorb water and nutrients main function transport and to provide a structure to connect the smaller diameter, fine roots to the rest of the plant.
- 67. Fine Roots Primaryroots usually <2 mm diameter that have the function of waterand nutrient uptake. They are often heavily branched and support mycorrhizas. These roots may be short lived, but are replaced by the plant in an ongoing process of root 'turnover'.
- 68. Storage Roots theseroots are modified for storage of food or water, such as carrots and beets. They include some taproots and tuberous roots.
- 69. Stilt Roots these are adventitious support roots, common among mangroves. They grow down from lateral branches, branching in the soil.
- 70. Structural Roots largeroots that have undergone considerable secondary thickening and provide mechanical support to woody plants and trees.
- 71. Haustorial Roots rootsof parasitic plants that can absorb water and nutrients from another plant, such as in mistletoe (Viscum album) and dodder.
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- 85. Anchorage andsupport
- 86. Absorption andconduction
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