(GA3) The first of the *gibberellins
to be isolated and characterized. It was obtained from the fungus Gibberella fujikuroi, which causes a disease of rice seedlings characterized by excessive elongation of shoots and leaves. The basic structure of gibberellic acid and most other compounds with gibberellin-like activity is the gibbane carbon skeleton (see diagram). Gibberellic acid is a terpenoid and is synthesized from mevalonic acid. Other gibberelhns are synthesized by the same pathway and there is probably much interconver-sion in the plant between the different gibberelhns. Gibberellic acid is the gibberellin most widely used in experiments.
The gibbane skeleton.