Bachelor’s Degree Programme (BSCG) – Plant Physiology and Metabolism Assig. Answer | BBYCT–137(Q-8)

Bachelor’s Degree Programme (BSCG) – Plant Physiology and Metabolism Assig. Answer | BBYCT–137(Q-8)

8. Enumerate the naturally occurring hormones in plants. Discuss the discovery, structure, mode of action, and practical applications of any one of them. 

Answer – Plant hormones are chemical compounds present in very low concentrations in plants. And, these hormones are naturally occurring in plants are indole (auxins), terpenes (Gibberellins), adenine (Cytokinins), carotenoids (Abscisic acid) and gases (Ethylene).
Auxin Hormone
Auxin means “to grow”. They are widely used in agricultural and horticultural practices. They are found in growing apices of roots and stems and then migrate to other parts to act.

  • Natural: Indole-3-acetic acid (IAA), Indole butyric acid (IBA)
  • Synthetic: 2,4-D (2,4-Dichlorophenoxyacetic acid), NAA (Naphthalene acetic acid)


Mode of action & Practical applications:

  • Cell elongation of stems and roots
  • Apical dominance, IAA in apical bud suppresses the growth of lateral buds
  • Induces parthenocarpy i.e. development of fruit without fertilization e.g. in tomatoes
  • Prevents premature fall of leaves, flowers, fruits
  • Useful in stem cuttings and grafting where it initiates rooting
  • Promotes flowering e.g. in pineapple
  • 2,4-D is widely used as a herbicide to kill undesirable weeds of dicot plants without affecting monocot plants
  • Helps in cell division and xylem differentiation

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