Gibberellins are a closely related group of phytohormones – with one or more carboxyl I groups attached to a gibbance ring skeleton (Cross et.al. 1961).
There are other compounds like Kaurene which have the actions similar to gibberellin but do not possess the gibbane ring.
These are called gibberallin like compounds. Gibberellins (abbreviated as GA) were first discovered by E.Kurusawa in 1926 as the active substance produced by the fungus Gibberella fujikuroi responsible for Bakanae or “Foolish disease” of rice in Japan. This disease causes excessive growth in the heights of the rice plants.
Cross etal isolated about six gibberellins named as GA1 to GA6 and established their structures. Till date, more than 50 gibberellins are known. Gibberellins are synthesized in different parts of the plants and their translations are non-polar. Gibberellins are translocation in both xylem and phloem.
1. Gibberellins are responsible for light induced inhibition of stem growth in many plants like Pisum sativum.
2. GA promotes cell division in meristems and elengation of internodes. In certain plants like pisum sativum, Viciafaba and Phaseolus multiflorus application of gibberellins have resulted in overcoming genetic dwarfism due to elongation of internodes.
3. It breaks seed dormancy in species like lettuce and tobacco.
4. Promote activities of certain enzymes like amylase and several other hydrolases.
5. Gibberellins are more efficient than auxins in inducing parthenocarpy (Wittwer and Bukovac 1957).
6. Induce flowering and fruiting in long day plants.