Gibberellins

• Gibberellins (GAs) are plant hormones that regulate growth and influence various developmental processes, including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction, and leaf and fruit senescence
• Gibberellin was first recognized in 1926 by a Japanese scientist, Eiichi Kurosawa, studying bakanae, the “foolish seedling” disease in rice
• It was first isolated in 1935 by Teijiro Yabuta and Sumuki, from fungal strains (Gibberella fujikuroi) provided by Kurosawa
• Yabuta named the isolate as gibberellin
• They are found in several forms: GA-1, GA-2, GA-3……………………..GA-60
• The first gibberellins to be obtained was gibberellin GA-3. Now 52 gibberellins have been identified from different groups of plants

Role of Endogenous Gibberellins

• Apical bud dormancy

• Cell elongation
• Fruit growth
• Flowering
• Metabolisation of food in seed storage cells

Practical Applications of Gibberellins:

• Germination: Increases length of hypocotyl and cotyledon leaf area
• Root Growth: Inhibits root growth
• Leaf Expansion: Leaves become broader and enlarged (Cabbage, Sweet corn)
• Hyponasty of leaves: GA treated leaves of chrysanthemum plants holds their leaves more erect
• Flowering: Induces flowering in long day plants and in plants requiring cold induction and also promotes formation of male flowers
• Parthenocarpy: Brinjal, Guava (Allahabad round, Thomson seedless)
• Fruit setting: Increased fruit setting (Sweet lime, Grapes)
• Fruit Drop: Not much effective
• Stem elongation: Chorchorus capsularis: extension of stem and increased number of internodes