cpac 14

• Gibberellins


  A type of plant hormone, the effects of which include the stimulation of elongation at cell internodes, the growth of fruit, and germination
• Germination


  1. Starch stored in the endosperm is converted to glucose

  2. Gibberellins are secreted by the embryo, which has been activated by the absorption of water

  3. Gibberellins diffuse to the aleurone layer of the endosperm

  4. Aleurone layer is stimulated to produce amylase

  5. Amylase hydrolyses the starch (amylose and/or amylopectin) into glucose
• Equipment


  • Cereal grains
  • Sodium hypochlorite solution
  • Muslin
  • Beaker
  • Scalpel
  • Forceps
  • Sterile containers to soak the grains
  • Tile
  • 1M gibberellic acid
  • Distilled water
  • Petri dishes
  • Adhesive tape
  • Potassium iodide solution
  • Measuring cylinder
• Method


  1. Dilute the stock gibberellin solution to several set concentrations

  2. Collect the required number of seeds and pull any husks off the grains

  3. Cut the seeds in half (one half should contain the embryo and the other half should contain the endosperm)

  4. Discard the half containing the embryo

  5. Sterilise the half containing the endosperm by placing it in the sodium hypochlorite solution and leaving for 3 minutes

  6. Wash the seeds through distilled water 5 times until there is no smell of bleach

  7. Place the seed halves in the gibberellin solution and leave for 12-48 hours

  8. Use sterile forceps to move seed halves onto a sterile petri dish with starch agar

  9. Partially tape the lids (to prevent conditions becoming anoxic)

  10. Leave for 12-48 hours

  11. Pour potassium iodide onto the plates

  12. Measure the zone of inhibition/'clear zone; around the seed half
• Hazards


  • Biohazard (allergies, soil bacteria, contamination)
  • Cuts from sharp objects
  • Irritant (sodium hypochlorite/gibberellic acid)
  • Cuts from scalpel
• Zone of inhibition


  Clear area around the seed half where starch had been digested
• As gibberellin concentration increased


  The amount of amylase produced by the aleurone layer increased, so area of starch from the agar around the seed half digested also increased
• The area where starch had been digested appeared as a clear area around the seed half