1. 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)
¤ 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

2. 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

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

4. 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

5. 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

6. 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

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

9. 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