Gibberellin is a plant hormone that promote elongation. It is isolated from a fungus; used in promoting plant growth. Synthesis occurs mainly in leaves and roots. They function by stimulating cell division and the hydrolisis of sugars to glucose and fructose, and stimulate extensive growth, expecially of internodes. Their effects oppose those of auxins. Gibberellins are known to be involved in the regulation of division and gene expression.

Gibberellin released by the embryo travels towards the aleurone layer, its target tissue situated in the endosperm region of the seed (alongside the embryo). Gibberellin acts as the inducer, as its presence allows the enzyme induction of amylase, which can break down starch INTO a sugar to be used in the embryo. Sugar is used in the plant to synthesise proteins and break out of dormancy. Gibberellins initiate this process in Summer, when the external environment exhibits favourable conditions for plant growth.

The family of gibberellins have a similar effect to that of auxins; they promote cell division and elongation. The major difference is that gibberellins in no way inhibit growth. Gibberellins (GAs) has been shown to be endogenous growth regulators by restoring the height of dwarf mutants of pea and maize by application of GA3, obtained from the fungus, Gibberella fujikuroi.

Gibberellins (GAs) are a group of diterpenoid acids that function as plant growth regulators inflencing a range of developmental processes in higher plants including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction and leaf and fruit senescence. The origin of research into gibberellins can be traced to Japanese plant pathologists who were investigating the causes of the "bakanae" (foolish seedling) disease which seriously lowered the yield of rice crops in Japan, Taiwan and throughout the Asian continent.

Gibberellin, GA4, GA4+7
Chemical name: Gibberellin(GA4, GA4+7)
Molecular formula: C19H24O5.C19H22O5
Molecular Weight: GA4 332.29, GA4+7 330.37