Gibberellic Acid in Plants

Introduction

• Gibberellic acid is a plant hormone.
• Key topics:
  • Production and occurrence
  • Functions
  • Biosynthesis pathway
  • Signaling

Production and Occurrence

• Locations of Production:
  • High concentrations in young roots and germinating seeds.
  • Also found in developing shoot tissues, embryos.
  • Production increases in dark conditions.
• Synthesis:
  • Starts from acetyl-CoA.

Biosynthesis Pathway

• Begins with isopentyl pyrophosphate (IPP).
• Major Steps:
  • IPP combines with dimethylalil diphosphate (DMAPP) to form geranyl diphosphate (GPP).
  • Addition of IPP units increases carbon chain (15C farnesyl diphosphate (FPP), 20C geranylgeranyl diphosphate (GGPP)).
  • GGPP converts to ent-copalyl diphosphate (via copalyl diphosphate synthase).
  • Converts to ent-kaurene by kaurene synthase.
  • Ent-kaurene processes in rough endoplasmic reticulum to form GA12, the primary gibberellin.
  • GA12 further modified into various other gibberellins (GA1, GA2, GA53, GA20).

Functions

• Cell Elongation:
  • Stimulates cell growth and expansion by increasing cell wall plasticity.
  • Increases water retention and pressure.
• Other Functions:
  • Induces flowering in biennial plants.
  • Breaks seed dormancy.
  • Facilitates parthenocarpic fruit development.
  • Affects sex expression and pollen germination.
  • Stimulates root growth and delays senescence.
  • Stimulates alpha-amylase production which aids in converting stored carbohydrates to energy in germinating seeds.
  • Influences internodal elongation.

Signaling Pathway

• Without Gibberellic Acid:
  • DELA repressor binds to GID1, inhibiting gibberellic acid-specific gene transcription.
• With Gibberellic Acid:
  • Gibberellic acid associates with GID1.
  • Involves SCF complex for ubiquitination and degradation of DELA repressor.
  • Results in GS-specific gene transcription.
• Gibberellic acid presence turns on signaling; absence turns it off.

Conclusion

• Covered gibberellic acid's properties, synthesis, signaling, and functions.
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