Gibberelline

Gibberellin refers to a large family of diterpenoid plant hormones that regulate growth and development in many higher plants. They were first isolated from the fungus Gibberella fujikuroi, which causes the bakanae disease in rice, and the name derives from this genus. The term gibberellin encompasses numerous related compounds, including GA1, GA3, and GA4, which are among the most active in various species.

Biosynthesis and signaling occur mainly in young tissues such as developing shoots, leaves, seeds, and embryos. More than 100 gibberellins have been identified, differing in activity. Plant perception involves the GA receptor GID1; upon GA binding, GID1 promotes interaction with DELLA proteins, repressors of growth. This interaction targets DELLA for ubiquitination and proteasomal degradation, releasing growth-promoting genes from repression and enabling cell expansion and division.

Roles of gibberellins are diverse. They promote seed germination by activating enzymes that mobilize stored nutrients, stimulate stem elongation and leaf expansion, and influence flowering time and fruit development. Their effects are often modulated by cross-talk with abscisic acid and are highly species- and tissue-specific.

Distribution and regulation are influenced by environmental and developmental cues. Gibberellins are synthesized in several tissues and transported through the plant, with levels responsive to light, temperature, gravity, and stress.

Applications include agricultural and horticultural use to promote germination, break seed dormancy, increase fruit size, and improve malting quality. GA3 is among the most widely used gibberellins commercially, though responses vary by species and cultivar.