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.
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“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
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
Enzyme involved in protein modification - enhances activity of GAI and RGA
CONTROL + GA3 GA3 + ABA (ABSCISIC ACID)
Low Cytoplasmic [Ca2+] High