ROOT APEX

the top three theories of root apical meristem in plants. The theories are: 1. Apical Cell Theory 2. Histogen Theory 3. Korper-Kappe Theory.The root apical meristem, or root apex, is a small region at the tip of a root in which all cells are capable of repeated division and from which all primary root tissues are derived. The root apical meristem is protected as it passes through the soil by an outer region of living parenchyma cells called the root cap.

1. WELCOME Presented by HEMANT DARJI

2. GOVIND GURU TRIBLE UNIVERSITY,BANSWARA TOPIC-ROOT ORGANIZATION SUBMITTED TO: LEENA MA’M SUBMITTED BY: HEMANT DARJI M.SC.(BOTANY) 2 nd SAMASTER

3. ROOT SYSTEM 1. Root is the descending or underground part of the plant axis. 2. Root is usually cylindrical and non-green (lack chlorophylls), but sometimes green as in Trapa and Taeniophylum . 3. The growing point of root tip is sub- terminal and protected by a root cap or calyptra . 4. Unicellular root hairs present just behind the root caps which increase the absorptive surface area of roots. 5. Lateral roots are endogenous in origin i.e. arise from pericycle of the main root. characteristic features of root- Root is usually positively geotropic (grows downward into the soil) and positively hydrotropic ( grows towards the source of water) but negatively phototropic . Root does not bear nodes, internodes, leaves or buds (exceptions are sweet potato, wood apple etc.)

4. TYPES OF ROOTS ON THE BASIS OF THEIR ORIGIN ROOT ARE FOLLOWING TYPE – TAP ROOT ,ADVENTITIOUS ROOT & FIBROUS ROOT TAP ROOT - On germination of a seed, the radicle elongates into primary root or true root or tap root. In dicot plants, the tap root is persistent and produces lateral roots such as secondary’ roots, tertiary roots etc. - All lateral roots arise in acropetal succession i.e. younger roots towards apex and older roots towards base. The tap root and its branches constitute the tap root system.

5. These are the roots that grow from any part of the plant other than radicle . In monocot plants, the tap root is short lived and soon replaced by adventitious roots. A group of adventitious roots and their branches constitute adventitious root system. Adventitious root -

6. FIBROUS ROOT Fibrous roots are composed a large Numbers of roots nearly equal in size . This type root system found in the Grasses.

7. ROOT APEX ORGANISATION Root apex is sub terminal in position because of terminal position of root cap. Root apex is of few types depending on the mode of origin of cap and relations between histogens and primary tissue regions of the root proper. The following three theories of Root apex organization are discussed below- 1. Apical Cell Theory 2. Histogen Theory 3. Korper-Kappe Theory.

8. Apical Cell Theory- This theory was proposed by Nageli who drew the attention to the occurrence of a single apical cell or apical initial that composes the root meristem . - The apical initial is tetrahedral in shape and generates root cap from one side. -The other three sides donate cells to form epidermis, cortex and vascular cylinder . - Apical cell theory is confined to vascular cryptogams only as the root apical meristem of flowering plants does not have a single apical cell.

9. Hanstein in 1868 advocated the theory. According to Hanstein root apical meristem consists of three cell-initiating regions called histogens . The histogens are called dermatogen , periblem and plerome that respectfully form epidermis, cortex and vascular cylindrical that are present in a mature root. 2. Histogen Theory-

10. 3. Korper-Kappe Theory (1917)-   The theory says that the cells in the root apex divide in a pattern called T-divisions. The cells of this region divide first horizontally. The lower daughter cell then divides longitudinally, i.e. at right angles to the plane of the first division. Thus the planes of the two divisions form a T in a median longitudinal section of the root. The inner region of the apex is the korper . In this region the T is inverted, the second division takes place in the upper daughter cell.

11. ROOT ORIGINETED FROM MERISTEM Apical meristem produces the cap Cell divisions at the apical meristem cause the root to lengthen Farther up, cells differentiate and mature.

12. ROOT HAIR Developed from the epidermal cells away from the root tip Increasing the surface area available for water and mineral absorption. Epidermis functions in the uptake of water and minerals Large surface area facilitates uptake.

13. TISSUES OF ROOT Root tissues can be regarded as a series of concentric rings of different tissues.

14. Epidermis -Single layer of cells on the exterior of the root not covered with a cuticle. -Root is designed for water uptake. -Cuticle is a barrier to water. -Comprised of large undifferentiated cells . -Functions in the storage of food reserves (proteins and starches) in root tissues. Cortex

15. Endodermis – Single layer of cells outside vascular system .Spaces between the cells are covered with a waxy layer, called suberin . Blocks passage of water and dissolved nutrients into the vascular system . Endodermis functions to regulate the uptake of water and nutrients into the plant .

16. A thin layer of undifferentiated cells. A meristem tissue The source of new lateral, or secondary, roots. Surrounds the vascular bundles. pericycle

17. Vascular tissue The transport system 1. Phloem – Living cells comprised of seive tube elements and companion cells. 2.Cambium – A meristematic tissue supplying cells that will develop into vascular structures. 3.Xylem – Dead cells with thickened cell walls, typically larger than phloem cells.

18. -Functions in the transport of water and mineral nutrients.

19. A LONG LOOK AT THE ROOT Where cells elongate and differentiate Pushes the root tip throh the soil . A longitudinal section through the root (from bottom to top) shows these various tissues and how they develop. 1. Elongation zone 2. Maturation zone Cells develop their final form Root hairs form, xylem cells thicken and die.

20. INTERNAL STRYCTURE OF ROOT

21. THE FUNCTIONS OF ROOT Anchoring of the plant to the soil. Absorption of water and nutrients from the soil. Conduction of absorbed water and nutrients to stem. Storage of food. Vegetative reproduction and competition with other plants.

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