Plant Growth Hormones

Plant Growth Hormones

  • Generally, there are five types of plant hormones, namely auxins, gibberellins (GAs), cytokinins, abscisic acid (ABA) and ethylene.
  • Auxins, gibberellins, cytokinins are plant growth promoters while abscisic acid and ethylene are plant inhibitors.


  • F. W Went discovered auxins.
  • The chief naturally occurring auxins are indole acetic acid (IAA), indole butyric acid (IBA).
  • Naphthalene acetic acid (NAA) is a root promoting hormone.
  • functions of auxins : promotion of stem elongation and growth; formation of adventitious roots; inhabitants of leaf abscission; promotion of cell division.


  • Gibberellins was discovered by kurosawa.
  • It delays senescence in fruits.
  • Involved in leaf expansion
  • Break bud and seed dormancy.
  • Used to fasten the maturity period in young conifers and promote early seed production.
  • Gibberellins are acidic in nature.


  • Skoog and Miller discovered cytokinins.
  • It breaks bud and seed dormancy.
  • Promotes cell division and apical dominance.
  • They used to keep flowers fresh for a longer time.
  • Promote later shoot and adventitious shoot.
  • Removes extra flowers for good growth.
  • Used in tissue culture.

Abscisic acid

  • Stimulates closing of stomata in the epidermis.
  • Inhabits plant metabolism and seed dormancy.
  • It is widely used as a spraying agent on trees to regulate dropping of fruits.


  • Ethylene is a gaseous plant growth regulator.
  • Ethylene is used as both plant growth promoter and plant growth regulator.
  • It promotes fruit ripening and agening tissue.
  • Affects horizontal growth of seedlings and swelling of the axis in dicot seedlings.
  • Increase root growth and root hair formation. Therefore helping plants to increase their development of plants.
  • Ethrel is a powdered form of ethylene.

Florigenes : promotes flowering.

Traumatic acid : wound healing hormone.

Also Read :

plant kingdom

cell and its Components

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