Plant Growth Factors

• Plants respond to:

  • light
  • gravity
  • water
• Phototropism in plants

  • Cells in shoot tip produce IAA, which is transported down the shoot
  • Light causes the movement of IAA from the light side to shaded side of the root
  • So the IAA builds up on the shaded side
  • IAA causes elongation of shoot cells, so more IAA in thenshaded side means more elongation
  • This causes the shoot tip to bend towards light
• Gravitropism in plants

  • IAA is transported along the root
  • IAA builds up on the lower side of the root
  • IAA inhibits the elongation of root cells, so these cells elongate less than those on the upper side
  • This causes the root to bend towards gravity