Gibberellins

• It was first extracted from the ascomycetous fungus Gibberella fujikuroi, the causal organism of the “foolish seedling of rice” commonly called bakany 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 genes.
• GA appears to involve the 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 Flowering

Ø Metabolization of food in seed storage cells.

Practical Applications of Gibberellins

Ø Germination: Increases length of hypocotyls and cotyledonary 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 hold their leaves more

erect.

Ø Flowering: Induces flowering in long-day plants and plants requiring cold induction. Also promotes the formation of male flowers.

Ø Parthenocarpy: Brinjal, Guava(Allahabad round). Thomson seedless

Ø Fruit setting: Increased fruit setting (Phalsa, Sweet lime, Grapes).

Ø Fruit Drop: Notveryh effective.

Ø Stem elongation: Chorchorus capsularis: extension of stem and increased number of internodes. However, leaf area, basal diameter of the set,m, and fiber 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 long days or red light. GA overcomes this dormancy. Enhanced cell elongation pushes through the endosperm (seed coat) Potato tubers can be made to sprout in winter by GA.