DISCOVERY OF GIBBERELLINS
1. “BAKANAE” OR “FOOLISH SEEDLING” DISEASE OF RICE : plants grew
too talkk and toppled over.
2. JAPANESE SCIENTISTS WORKED ON THE PROBLEM AND IDENTIFIED
CAUSE: INFECTION BY FUNGUS, GIBBERELLA FUJUKUROI.
3. MID 1950s: ACTIVE SUBSTANCE CRYTALIZED AND IDENTIFIED IN
ENGLAND AND US: GIBBERELLIC ACID (GA3)
Rice leaf sheath bioassay for
gibberellin
Increasing GA3 concentration
GIBBERELLIN BIOSYNTHESIS AND METABOLISM
1. GIBBERELLINS ARE SYNTHESIZED VIA THE TERPENOID
PATHWAY.
2. BASED ON ISOPRENE UNITS:
3. BIOLOGICAL ISOPRENE UNIT = ISOPENTENYL DIPHOSPHATE
LOCATIONS OF
SOME MUTANT
GENES THAT
BLOCK GA
BIOSYNTHETIC
PATHWAY IN
PEA
GA1, THE BIOLOGICALLY ACTIVE GIBBERELLIN, IS
SYNTHESIZED FROM GA20
GA1 LEVELS CORRELATE WITH INTERNODE LENGTH
Phenotypes and
genotypes of
peas with
different
gibberellin levels
Luciferase reporter construct for GA 20-oxidase
HIGHEST IN
APICAL BUD
EFFECT OF AMO-1618 ON PETIOLE ELONGATION OF
SPINACH
EFFECT OF LONG DAYS ON GA LEVELS IN SPINACH
Effect of Long Days (High GA levels) on Tuber
Formation in Potato
Long Days
Short Days
Genetically Engineered Dwarf Wheat
Plants Overexpressing GA 2-ox, which
degrades GA1
KINETICS OF
GA-INDUCED
ELNGATION OF
DEEPWATER
RICE
INTERNODE
30 min
DISTRIBUTION OF CELL DIVISION FOLLOWING GA TREATMENT OF
A ROSETTE PLANT, Samolus parviflorus
Arabidopsis GIBBERELLIN RESPONSE MUTANTS WITH
DEFECTS IN SIGNAL TRANSDUCTION
1. Gibberellin-in sensitive dwarfs
2. Gibberellin-deficient mutants in which GA deficiency
has been overcome by a second suppressor mutation,
so plant looks normal (double mutant)
3. Mutants with constitutive gibberellin response
(“slender” mutants)
GAI and RGA are related repressor proteins
Repression of GA
Response Genes
GA Response
Genes
Expressed
DIFFERENT TYPES OF MUTATIONS OF GAI AND RGA
REPRESSORS AFFECT GROWTH DIFFERENTLY
GA acts to
block action
of both SPY
and
GAI/RGA
Enzyme
involved in
protein
modification enhances
activity of
GAI and RGA
THE CEREAL
ALEURONE LAYER
EFFECT OF GA ON CALCIUM IN BARLEY ALEURONE
LAYER PROTOPLAST
CONTROL
Low
+ GA3
Cytoplasmic [Ca2+]
GA3 + ABA (ABSCISIC ACID)
High
SUMMARY OF STEPS
IN GA SIGNAL
TRANSDUCTION
PATHWAY