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.
- 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 :