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Plant Hormone Gibberellins : Major Functions

Japanese farmers noticed abnormal growth of young infected rice plants they called “Bakanae or foolish seedling” causative agent was fungus Fusarium moniliforme, the imperfect stage of Gibbbereella fujikuroi of Ascomycetes. 

      Named as GA1, GA2,GA3…
Most significant and well studied GA3
  •  GA1 – in elongation
  •  GA9- in flowering
  •  Gibberellins distribute throughout the plant kingdom in ferns, mosses
  •  GA5 is responsible for ‘super elongation’ disease of Cassava.
Synthesis : Isoprenoid pathway
Mobilization of reserve food, How?
  • Events in barley seed germination
  • Embryo is activated by imbibitions of water
  • Gibberellin is produced in the embryo
  • It diffuses into the aleurone layer
  • Then  induces synthesis of digestive enzymes α-amylase, protease
  • Enzyme converts starch to sugars and proteins to aminoacids including tryptophan
  • Tryptophan thus produced is translocated to the coleoptiles tip
  • There it is converted to IAA
  • IAA moves from the coleoptiles tip to the base
  • Coleoptiles cell wall become weakened
  • Water is taken up and cell enlarges 
Major Effects
Stem elongation

Elongation of dwarf plants
Elongation of dwarf plants (Rosette plants)
Promote flowering
Synthesis of auxin by Gibberellin? 
Gibberellin>protease->protein->tryptophan->auxin
  •     Induce parthenocarpy
  •     Breaking dormancy
Transport: non-polar through phloem
What are Anti Gibberellins?
  •        Compounds interfere with Gibeberellin biosynthesis 
  •         eg: (2-chloroethyl) tri methyl ammonium chloride or cycocel (CCC), phosphon-D and alar

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