Tropisms

• Tropisms

  Growth or turning movement of a plant in response to a directional external stimulus
• Types of tropisms

  • Phototropism
  • Geotropism (or gravitropism)
  • Hydrotropism
  • Thigmotropism
• Phototropism

  Light receptors (phototropins) trigger the redistribution of auxin to the dark side of the plant
• Geotropism

  Auxin will accumulate on the lower side of the plant in response to the force of gravity
• High auxin concentrations in shoots

  Promote cell elongation
• High auxin concentrations in roots

  Inhibit cell elongation
• Phototropism in shoots

  • The dark side of the shoot elongates and shoots grow towards the light (positive phototropism)
• Geotropism in shoots

  • The lower side of the shoot elongates and roots grow away from the ground
• Phototropism in roots

  • The dark side of the root becomes shorter and the roots grow away from the light (negative phototropism)
• Geotropism in roots

  • The lower side of the root becomes shorter and the roots turn downwards into the earth