DISCOVERY OF GIBBERELLINS. “BAKANAE” OR “FOOLISH SEEDLING” DISEASE OF RICE : plants grew too talkk and toppled over. JAPANESE SCIENTISTS WORKED ON THE PROBLEM AND IDENTIFIED CAUSE: INFECTION BY FUNGUS, GIBBERELLA FUJUKUROI.
“BAKANAE” OR “FOOLISH SEEDLING” DISEASE OF RICE : plants grew too talkk and toppled over.
JAPANESE SCIENTISTS WORKED ON THE PROBLEM AND IDENTIFIED CAUSE: INFECTION BY FUNGUS, GIBBERELLA FUJUKUROI.
MID 1950s: ACTIVE SUBSTANCE CRYTALIZED AND IDENTIFIED IN ENGLAND AND US: GIBBERELLIC ACID (GA3)
Increasing GA3 concentration
GIBBERELLINS ARE SYNTHESIZED VIA THE TERPENOID PATHWAY.
BASED ON ISOPRENE UNITS:
BIOLOGICAL ISOPRENE UNIT = ISOPENTENYL DIPHOSPHATE
LOCATIONS OF SOME MUTANT GENES THAT BLOCK GA BIOSYNTHETIC PATHWAY IN PEA
HIGHEST IN APICAL BUD
Genetically Engineered Dwarf Wheat Plants Overexpressing GA 2-ox, which degrades GA1
KINETICS OF GA-INDUCED ELNGATION OF DEEPWATER RICE INTERNODE 2-ox, which degrades GA
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)
Repression of GA Response Genes
GA Response Genes Expressed
GA acts to block action of both SPY and GAI/RGA AFFECT GROWTH DIFFERENTLY
Enzyme involved in protein modification - enhances activity of GAI and RGA
THE CEREAL ALEURONE LAYER AFFECT GROWTH DIFFERENTLY
CONTROL + GA3 GA3 + ABA (ABSCISIC ACID)
Low Cytoplasmic [Ca2+] High
SUMMARY OF STEPS IN GA SIGNAL TRANSDUCTION PATHWAY AFFECT GROWTH DIFFERENTLY