gibberelliner

Gibberellins are a large family of diterpenoid plant hormones that regulate growth and development. They were first identified in 1926 from the fungus Gibberella fujikuroi, which causes the foolish seedling disease in rice; the name derives from this fungus. More than 100 gibberellins have been described, with GA1, GA3, GA4 and GA7 among the most biologically active in many species.

Biosynthesis occurs in plastids via the terpenoid pathway, starting from geranylgeranyl diphosphate to ent-kaurene and proceeding through multiple oxidations to bioactive gibberellins. Key enzymes include ent-kaurene synthase, ent-kaurene oxidases, GA20-oxidase and GA3-oxidase. The production and activity of active gibberellins are influenced by light, temperature, nutrients, and interactions with other hormones such as abscisic acid.

Mechanistically, gibberellins function by binding to the GA receptor GID1, promoting degradation of DELLA repressor proteins and thereby activating growth responses. In seeds, they trigger the production of hydrolytic enzymes in the aleurone layer to mobilize stored nutrients; in vegetative tissues they promote cell elongation and division, contributing to stem growth and impacting flowering time and fruit development in various crops.

Applications of gibberellins in agriculture include breaking seed dormancy, promoting germination, increasing fruit size and uniformity in some crops, and aiding malting by stimulating enzymatic activity in cereal grains. Dwarfing varieties can arise from reduced GA biosynthesis or signaling, and GA biosynthesis inhibitors are used to limit excessive growth in horticulture.

Gibberellins remain fundamental to plant physiology and crop improvement, reflecting their central role in growth regulation and environmental response.