gibberellin The generic name of a group of plant hormones that stimulate the growth of leaves and shoots. Unlike auxins, they tend to affect the whole plant and do not induce localized bending movements. They are thought to act either at a transcriptional level or as inducers of enzymes. Gibberellins were first isolated from a fungus, Gibberella fujikuroi, and were found to be the cause of bakanae disease (a disease of rice, known in Japan as ‘foolish seedling disease’), in which affected plants grow unusually tall but seldom survive to maturity.

gibberellin Any of a group of plant growth substances chemically related to terpenes and occurring naturally in plants and fungi. They promote elongation of stems, e.g. bolting in cabbage plants, and the mobilization of food reserves in germinating seeds, and are influential in inducing flowering and fruit development. Commercially available gibberellins, such as gibberellic acid, are used to manipulate the onset of sexual maturity in various species, e.g. to induce cone-bearing in young conifer trees.

gibberellin Any of a group of plant hormones that stimulate cell division, stem elongation and response to light and temperature. They have been used to increase crop yields.

gib·ber·el·lin / ˌjibəˈrelin/ • n. any of a group of plant hormones that stimulate stem elongation, germination, and flowering.