Discovery of gibberellins
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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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Discovery of gibberellins
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.

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
GIBBERELLIN BIOSYNTHESIS AND METABOLISM

GIBBERELLINS ARE SYNTHESIZED VIA THE TERPENOID PATHWAY.

BASED ON ISOPRENE UNITS:

BIOLOGICAL ISOPRENE UNIT = ISOPENTENYL DIPHOSPHATE



Ga 1 the biologically active gibberellin is synthesized from ga 20
GA PATHWAY IN PEA1, THE BIOLOGICALLY ACTIVE GIBBERELLIN, IS SYNTHESIZED FROM GA20


Ga 1 levels correlate with internode length
GA PATHWAY IN PEA1 LEVELS CORRELATE WITH INTERNODE LENGTH










Arabidopsis gibberellin response mutants with defects in signal transduction
Arabidopsis ROSETTE PLANT, 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
GAI and RGA are related repressor proteins ROSETTE PLANT,

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


Effect of ga on calcium in barley aleurone layer protoplast
EFFECT OF GA ON CALCIUM IN BARLEY ALEURONE LAYER PROTOPLAST AFFECT GROWTH DIFFERENTLY

CONTROL + GA3 GA3 + ABA (ABSCISIC ACID)

Low Cytoplasmic [Ca2+] High



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