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Explain the different zones of root apex with the help of a well-labeled diagram?

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A typical root can be differentiated into five regions. From apex to base they are:

(a) Root Cap (Calyptra):

  1. It is a cap like protective structure of the growing root tip.
  2. In Pandanus (screwpine) multiple root caps present while in aquatic plants (Pistia, Eichhomia, Lemna) root pockets present instead of root cap.

Function:

  • Protects root meristem,
  • Secrete mucilage that help tender root to penetrate the hard soil,
  • Helps in perception of gravity,
  • Root packets functions as balances.

(b)  Growing point or Meristematic Zone:

  1. It is about 0.25 – 1.0 mm long, lies just behind the root cap and thus sub-terminal in position.
  2. Its shape is like an inverted concave dome of cells.
  3. The central rarely dividing cells are called quiescent centre.

Function:

  • Root meristem adds cells to root cap and the basal region of the root.

(c) Zone of elongation:

  1. It is about 1 -10 mm long and lies just behind the meristematic zone.
  2. As the name implies, it is the site of rapid and extensive cell elongation.
  3. This zone increases length of the root.
  4. The external cells can absorb water and minerals from the soil.

(d) Root hair Zone or Zone of differentiation:

  1. It is about 1 – 6 cm long.
  2. It is the zone where cell differentiate to form epiblema, cortex, endodermis, pericycle, xylem and phloem.
  3. Many cells of epiblema elongate to form unicellular root hairs.
  4. As the root grows, new root hairs develop and older one shrivel and sloughed off.

Function:

  • Root hairs increase the absorptive surface area of root.

(e) Zone of maturation:

  1. It constitute the major portion of the root.
  2. The cells attain maturity when they reach this zone. 

Function

  1. Lateral roots may emerge from pericycle.
  2. Radial differentiation of tissues causes secondary growth in dicots.

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