.2 Tropisms

• phototropism: >growth in response to direction of light shoots are positively phototropic so grow toward roots are negatively phototropic so grow away
• gravitropism: >growth in response to direction of gravity shoots are negatively gravitropic so grow upward roots are positively gravitropic so grow downward
• co-ordination by plant

  growth factors

  made in cells can affect tissues that release them
• Indoleacetic Acid (IAA) -auxin that controls trophic responses in plants
• IAA-

  • transported over short distances (by DORAT) and longer (in phloem) around the plant
  • when a plant detects directional stimuli , IAA is transported to different parts of the plant, uneven distribution
  • where it is uneven, directional growth response occurs
• • phototropismIAA moves to shaded areasshoot bends toward the lightpositive phototropismroot bends away from the lightnegative phototropism
• • gravitropismIAA transported to the undersideshoot bends away from the gravitational pullnegative gravitropismroots bend toward gravitational pullpositive gravitropism