Two Types of Auxins and Physiological Role of Auxins

  • First plant hormone discovered was Auxin by Frits Went.
  • Tryptophan is the precursor for auxin. 
  • Auxin a- C18 H33 O& Auxin b - C18 H30O4 (IAA) exist in plants.
  • IAA is the active principle of Auxin.
Types of Auxins: Natural auxins and synthetic Auxins
Natural Auxins
Synthetic Auxins
  • IAA(Indole3- Acetic Acid)
  • Indole-3-acetaldehyde,
  • Indole-3-pyruvic acid
  • Indole-3-acetonitrile
  • Indole-3-ethanol
  • Phenyl acetic acid
  • Indole 3- Butyric Acid (IBA)
  • Indole 3-propionic acid
  • Indole Pyruvic acid
  • NAA- Napthelene Acetic acid
  • 2,4,D- 2,4, Dichlorophenoxy acetic acid
Synthetic auxins are more stable.
Physiological role of Auxins:
1. Auxins induce elongation of plant cells, roots, buds, stems, petiole, mid rib and major            lateral veins of leaf.
2. It is responsible for apical dominance.
3. Some of the auxin derivatives stimulate seed germination.
4. Some auxins promote cambial activity.
5. Root formation is stimulated by some auxins.
6. Auxins have been used to break seed dormancy.
7. It is responsible for callus formation in tissue culture.
8. They initiate early flowering and fruiting.
9. IAA induces parthenocarpy.
10. Some auxins inhibit the leaf fall and fruit fall.
11. Auxins are used as weed killers. 
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