Chapter 20 Gibberellins: Regulators of plant height

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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/gib
berellin_ 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
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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
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4-day-old rice seedlings (dwarf) were treated
with increasing amount of GA3 for 5 days, bioassay
Dosage dep.
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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
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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
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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
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Cyclization
The first GA The precursor of other GAs
B ring 6 ? 5 CH3 ? COOH
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homeostasis GA20ox, GA3ox negative feedback
regulation GA2ox positive feed-forward
regulation Fe2 ascorbate require GA20 ? GA5 ?
GA3
active inactive