- It was first extracted from the ascomycetous fungus Gibberella fujikuroi, the casual organisms of “foolish seedling of rice” or commonly called bakanae of rice
- Mechanism of Gibberellins: GA exerts its physiological effect on altering the Auxin status of tissue. It acts at the gene level to cause depressions of specific gene.
- GA appears to involve in alteration of nucleic acid directed protein synthesis in some long term regulatory action and some other types of activation phenomena in short term regulatory action.
Role of Endogenous Gibberellins
Ø Apical bud dormancy
Ø Role in sub apical meristem
Ø Cell elongation
Ø Fruit growth
Ø Metabolization of food in seed storage cells.
Practical Applications of Gibberellins
Ø Germination: Increases length of hypocotyls and cotyledenary leaf area.
Ø Root Growth: Inhibits root growth
Ø Leaf Expansion: Leaves become broader and enlarged (Cabbage, Sweet corn).
Ø Hyponesty of leaves: GA treated leaves of chrysanthemum plants holds their leaves more
Ø Flowering: Induces flowering in long day plants and in plants requiring cold induction. Also promotes formation of male flowers.
Ø Parthenocorpy: Brinjal, Guava(Alahabad round). Thomson seedless
Ø Fruit setting: Increased fruit setting (Phalsa, Sweet lime, Grapes).
Ø Fruit Drop: Not much effective.
Ø Stem elongation: Chorchorus capsularis: extention of stem and increased number of internodes. However leaf area, basal diameter of stem and fibre quality are reduced.
Ø Pollen Germination: Sugar cane 15 out of 34 germinated against normal conditions.
Ø Breaking Dormancy: In temperate plants buds become dormant in later summer and do not sprout even when exposed to sufficient moisture, temperature and oxygen. They require low temperatures or long days or red light. GA overcomes this dormancy. Enhanced cell elongation push through the endosperm (seed coat) Potato tubers can be made to sprout in winter by GA.