Gibberellines

Gibberellins are a group of plant hormones that regulate growth and development in many higher plants. They are diterpenoid acids produced mainly in young leaves and developing organs, as well as seeds, and they influence processes such as germination, stem elongation, flowering, and fruit set.

Gibberellins were first identified from a fungal pathogen, Gibberella fujikuroi, causing the foolish seedling disease of rice in the early 20th century. The active compounds were isolated in the 1940s, and GA3 emerged as a widely studied and commercially important member of the family.

Biochemically, gibberellins are synthesized via the terpenoid pathway in plastids and the cytosol, proceeding from ent-kaurene to various bioactive GAs such as GA1, GA3, GA4, and GA7. The mode of action involves binding to the GID1 receptor, which promotes degradation of DELLA growth-repressor proteins, releasing growth-promoting gene expression.

In plants, gibberellins promote seed germination by stimulating embryo growth, enhance stem elongation by loosening cell walls, regulate flowering time in annuals and perennials, and influence grain and fruit development. Their activity is balanced by other hormones, particularly abscisic acid, and environmental factors such as light and temperature.

Economically, gibberellins are used to improve vigor in some crops, to induce seed germination for malting, and to manipulate plant stature in ornamental and agricultural contexts. They can be applied as foliar sprays or seeds, while growth-inhibiting chemicals such as paclobutrazol are used to restrain excessive elongation.

Over 130 gibberellins have been identified, but only a subset are bioactive in most plants. GA1, GA3, GA4, and GA7 are among the most studied, with GA3 and GA4+7 formulations used in horticulture and agriculture.