Chapter 20 Gibberellins: Regulators of plant height ¤ 1950s, the second groups of hormones ¤ “foolish seedling” or bakanae ¤ a chemical secreted by Gibberella fujikuroi, GA3 ¤ C19 or C20, defined by their chemical structure, more than 125 (136) ¤ http://www.plant-hormone.info/gibberellin_ nomenclature.htm. ¤ GA1 identified from Phaseolus coccineus, 1958 ¤ GAx, x is the number in the order of their discovery ¤ only a few are biologically active

Physiological functions: increase in plant height particularly in genetically dwarf and rosette plants, but no effect on the genetically very tall plants Bolting: Stem growth Stem thickness, leaf size  A pale green color of the leaves

Dosage dep. 4-day-old rice seedlings (dwarf) were treated with increasing amount of GA3 for 5 days, bioassay Dosage dep.

GAs regulate the transition from juvenile to adult phases Stem injected the previous summer with GA4/GA7 mixture in aqueous ethanol Conebud formation 14-week-old Spray GA3 some 8 weeks earlier

Physiological functions: promote pollen development and tube growth influence floral initiation and sex determination Tassel + GA  female (pistillate) induction, suppress stamen (anther) development GA-deficient mutant p. 522 + GA3 - GA3 In dicots, GA seems to have the opposite effect GA / ABA

Physiological functions: promote fruit set: apple promote parthenocarpy promote seed germination: to overcome the dormancy Commercial applications: fruit production alleviating compaction delay senescence: citrus malting of barley increasing sugarcane yield plant breeding biosynthesis inhibitors lodging (used Cycocel), shrub plantings seedless grapes

Cyclization B ring: 6  5 CH3  COOH The first GA The precursor of other GAs

Fe2+ ascorbate require GA20  GA5  GA3 active inactive homeostasis GA20ox, GA3ox: negative feedback regulation GA2ox: positive feed-forward regulation Fe2+ ascorbate require GA20  GA5  GA3 active inactive