Gibberellins

Functions:

• Seed Germination--Barley de novo amylase synthesis (Varner 1964)
• Cell Expansion/Elongation
• Reverses dwarfism
• Bolting in biennials
• Flower induction?
• Control of sex expression
• Fruit Growth - Seedless grapes
• Delays Senescence

History:

• 1926 E. Kurosawa - foolish seedling disease in rice
  Gibberella fujikuroi (Fusarium moniliforme)
  culture medium causes disease symptoms
• 1935 T Yabuta names substance "gibberellin"
• 1938 isolates crystals of GA-A and GA-B
• War-effort stops work and commuications
• 1955 Stodola USDA Brian ICI London isolate Gibberellic Acid
• 1956 West and Phinney UCLA isolate GA from plants
• 1958 MacMillan Bristol England identifies GA1 from beans

Structure:

• 19 or 20-carbon polycyclic ring system
• Mono-, di-, or tri- carboxylic acid
• Forms vary by number and position of OH groups
• C7 COOH group is required
• conjugates with B-D-glucose
• Over 100 different forms- isomers, eantiomers, analogs
  Found in bacteria, fungi, angiosperms

Control of Level:

• Synthesis
  • from mevalonic acid, isoprene units, to GA
  • in isolated chloroplasts (T. C. Moore 1976)
  • can be blocked with
    • AMO-1618 (GGPP-/->CPPP)
    • CCC (after Kaurene)
    • Ancymidol (Kene-/->Kenol)
    • Dwarf Corn Blocked before K-ene
• Conjugation-likely to glucose or other sugars
• Transport non polar in transpiration and transloacation stream very rapid 5 cm/hr
• Interconversion: 100 forms different in activity levels
• Degradation:

Responses:

• Acid Growth Responses (typical...just like auxins)
• Sustained (typical)
• Unusual dose response:

  

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