Plant Hormones: Gibberellins

CHAPTER: 15(C)

Plant Hormones: Gibberellins

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 were gibberellin GA-3. Now 52 gibberellins have been identified from different groups of plants.

Structure of Gibberellins:

The structure of gibberellins consists of diterpenoid acids. These are synthesized in plastids through terpenoid pathway. Their modification occurs in the endoplasmic reticulum & cytosol. There are two classes of gibberellins based on carbon number, one containing 19 carbons and another containing 0 carbons. In case of 19 carbon gibberellins, carbon 20 is replaced by five members Lactone Bridge. It links carbon 4 and 10 in the structure of gibberellins.

Physiological roles of Gibberellins:

1.      Induces cell elongation:

This hormone helps in the elongation of internodes. Gibberellins increase the stem of plant.

2.      Stimulates enzyme activity.

Some enzyme in plants requires gibberellins to become activated.

3.      Able to overcome dwarfism by cell elongation:

Dwarfism of plants is prevented by this hormones by elongation the internodes.

4.      Promotes Germination, leaf expansion.

5.      Induce De-Novo synthesis of enzyme.

Practical Applications of GA in Agricultural:

1. Flowering

2. Germination
3. Apical Bud Dormancy
4. Rooting
5. Parthenocarpy
6. Fruit Growth
7. Increase fruit size and prevent cracking of fruits.
8. Induce internode elongation.
9. Prevent senescence in leaves.
10. Increase sugar content in sugarcane and induce alpha-amylase in barley brewing