Plant growth factors

• Example of growth factors in tropisms

  IAA - indoleacetic acid
• What is IAA?

  A type of auxin that can control cell elongation in shoots and inhibit growth of cells in the roots
• Where is IAA produced in a plant?

  tip of roots and shoots
• phototropism

  A growth response to light
• How does IAA move around the plant?

  diffusion
• phototropism in flowering plants process

  1. shoot tip cells produce IAA causing cell elongation

  2) IAA diffuses down the shoot

  3) if there is unilateral light, IAA diffusers towards the shaded side resulting in a higher concentration of IAA there

  4) cells on shaded side elongate more and results in plant bending towards the light source
• Gravitropism in flowering plants (roots) process

  1. cells in root too produce IAA which diffuses throughout root

  2) gravity influences movement of IAA to lower side of root therefore greater concentration on lower side

  3) IAA inhibits cell elongation in roots so lower side elongates less

  4) therefore roots grow downwards a upper side elongates causing a bend downwards
• IAA difference in root and shoots

  • causes cell elongation in shoots
  • inhibits cell elongation in roots
• reason for a positive phototropism

  light is needed in LDR