Gibberellins
1926 Japanese, Gibberella fujikuroi, gibberellin A
1954, 55 US UK
1958
1987
1991
GA1 in higher plant (GAx) synthesis/metabolism
84 GAs
1995
1996
1997
89 GAs (64 plants, 12 fungi and 13 both) more than 100 genes being cloned
Gibberellic acid (GA3)
End metabolic product in fungi
Plant GA20
Commercial
High activity
GA5 GA3
Slow degradation
Similar to GA1 (additional double bond)
GA4 GA7 nonpolar, slowly diffuse
GA9 GA12 precursor
GA29 GA34 deactivated form
Different tissues Different forms of GA
GA in fungi algae bacteria moss fern gymnosperm angiosperm growing, differentiated tissues young, developing, expanding leaves developing seeds/fruit elongated internode/petiole shoot/stem apex also in root cap/tip and xylem sap
GA synthesis and metabolism
Mevalonic acid pathway (cytosol)
Non mevalonic acid pathway (plastid)

From mevalonic acid (6C)
GGPP (20C)
ent kaurene (specific) phytol, GA, carotenoid
GA12 aldehyde (first GA)
GAx
In higher plants from GA12 aldehyde
Early 13-hydroxylation pathway (GA1)
Non 13-hydroxylation pathway (GA4) with GA20oxidase gene: pathway shifted GA4 GA1
All GAs: tetracyclic diterpenoid compounds
Isoprene unit
ent-Gibberellane skeleton
2 main types: C20-GA and C19-GA
GA derivatives by modification of 4 rings
C20 oxidation: CH
3
CH
2
OH CHO COOH
Hydroxylation: number, position and stoichiometry
Loss of C20
GA inactivation
2  -OH: GA20 GA29
GA8 GA1
C20 oxidation to COOH
Conjugation by glucose
Glycosylation: inactivate, storage and transport
Glucose via COOH: GA glycoside
Glucose via OH: GA glycosyl ether

In vegetative tissue: conserved synthetic pathway
13-OH path then 3  -OH
GA20 (C19-GA)
GA1 except: arabidopsis and cucumber: GA4
In seed: various pathway different GA
GA synthesis mutants
Pea na mutant: dwarf
ent-kaurene
Pea le mutant: dwarf exog. GA1 tall exog. GA20 no response cloned Le gene: 3  hydroxylase
GA20 GA1
Considering 2 loci
Na le GA20
na Le ent-kaurene
GA12 aldehyde
Grafting
1. na Le scion
Na le stock
2. Na le scion
Na Le stock tall dwarf
GA mechanism in elongation
Unlike auxin (acidification)
Inc. wall extensibility
Dec. minimum force for wall extension
By (may) dec. Ca conc in the wall inc. Ca uptake into the cell reduce crosslinking of lignin-related cpd
(via peroxidase)
GA mechanism in germination
Activate transcription of  amylase gene
In scutellum and aleurone

GA detection and assay
Bioassay
Easy but not specific
Fractionation Plant response
Lettuce hypocotyls elongation
Microdrop/dwar rice
 amylase production
GC-MS
Solvent extraction
Chromatography (polarity)
GC (bp)
MS (mass)
Identification and quantification
High sensitivity and more specific
GA inhibitors
Inhibit ent-kaurene synthesis
AMO1618 Cycocel
Inhibit ent-kaurene oxidation
Pac Uniconazol Ancymidol Tetcyclasis
Inhibit later step by dioxygenases
Bx-1112 LAB1988999