Gibberellins

b. Gibberellins : Gibberellins are another class of growth-promoting hormones, particularly abundant in root tips and developing seeds; unlike auxin, they are transported in a non-polar fashion through the vascular tissue. They were first isolated from the fungus Gibberella fujikuroi by the Japanese scientist Kurosawa in 1926, who had observed that rice plants infected by this fungus showed extreme stem elongation -- the 'bakane' or 'foolish seedling' disease. The active compound in crystalline form was isolated from fungal culture by Yabuta and Sumiki in 1938 and named gibberellin. In the plant itself, gibberellins are synthesised in young leaves, seeds, roots and stem tips from mevalonic acid; more than 150 distinct gibberellins are now known, of which GA3 (gibberellic acid) is the most common and biologically active, containing a gibbane ring built from four isoprene units. …