2' Auxins

1
2. Auxins

• e.g. IAA
• made continuously in the shoot apex and young
  leaves
• move basipetally (from apex to base of the organ)
• show different effects in shoot and root

2

• Experiment 1
• Unilateral illumination of coleoptiles

• Auxins move laterally away from light
• High concentration of auxins on the shaded side
  stimulates cell elongation ? curvature
• Shoot shows positive phototropism

3

• Experiment 2
• Horizontally placed seedling

• Auxins are accumulated on the lower side due to
  gravity

• In shoot high auxin concentration in lower side
  stimulates shoot growth? negative geotropism
• In root high concentration of auxins inhibits
  growth ? positive geotropism