Plant growth substances

1
Plant growth substances

• Auxin
• Gibberellin
• Abscisic acid

2
Auxin 1 Apical Dominance

• Auxin inhibits growth of lateral buds
• Auxin is made in the tip of a shoot
• So
• If the tip is intact, lateral buds dont grow
• If you remove the tip lateral buds grow

3
Auxin 2 Phototropism

• Moves to dark side of plant (Active process)
• High concentration on dark side causes cell
  elongation
• Tip of shoot pushed to light

4
Auxin 3 Leaf abscission

• Evidence for involvement
• Exact role is unclear

5
Gibberellin 1 Seed germination

• Used to control seed dormancy

• Seed absorbs water
• Gibberellin produced by embryo
• Amylase synthesized in aleurone layer
• Starch in endosperm is hydrolysed to maltose
• Maltose converted to glucose for respiration

6
Gibberellin 2 Stem elongation

• Synthesized in most parts of a plant
• Two types of gibberelin can be produced
• Active (dominant allele)
• Inactive (recessive allele)
• Active gibberellin promotes cell division and
  elongation
• Can be applied externally by farmers etc

7
Abscisic Acid

• Known as stress hormone
• Synthesized in most cells
• Released in adverse environmental conditions
• Causes stomata to close and thereby reduce water
  loss
• May inhibit proton pump (that allows K to
  diffuse into guard cells) thereby raising ? and
  reducing turgor

8
Summary

• Auxin
• Apical Dominance
• Phototropism
• Leaf abscission
• Gibberellins
• Seed dormancy
• Stem elongation
• Abscisic acid
• Stomatal closure due to stress
• (Leaf abscission)