Gibberelliinien

Gibberelliinien are a family of diterpenoid plant hormones that regulate growth and development in seed plants. They were first identified from the fungus Gibberella fujikuroi, the cause of the bakanae disease in rice, which gave rise to their name. Today, many gibberellins have been identified in plants, with GA1, GA3, GA4 and GA7 among the most biologically active in many species.

Biosynthesis and signaling: Gibberellins are synthesized from geranylgeranyl diphosphate via the terpenoid pathway in plastids, then modified in the cytosol. Key steps involve formation of ent-kaurene, followed by oxidation steps catalyzed by enzymes such as GA20-oxidase and GA3-oxidase to produce bioactive GA forms. The perception mechanism involves the GA receptor GID1, which binds active gibberellins and promotes degradation of DELLA transcriptional repressors, thereby enabling GA-responsive growth programs.

Physiological roles: In seeds, gibberellins promote germination by stimulating the production of hydrolytic enzymes that mobilize stored nutrients. They also regulate stem elongation, leaf expansion, flowering time, and fruit development. GA signaling interacts with other hormones such as auxin, brassinosteroids, and abscisic acid to integrate environmental conditions with growth.

Applications and regulation: Commercially, gibberellins are used to improve seed germination uniformity, increase fruit size in some crops (notably grapes and citrus), and control flowering and dormancy. They are also employed in malting to stimulate enzyme production. Because gibberellins have potent growth effects, their use is regulated and dosed to minimize lodging, unwanted elongation, or ecological impacts.

See also: gibberellins, plant hormones, DELLA proteins, GA signaling.