Plant Hormones

• Auxin:

  • Controls growth near tips of shoots and roots
  • Controls growth of plant in response to light (phototropism) and gravity (geo/gravitropism)
  • Produced in tips and moves backwards to stimulate cell elongation
  • If tip of shoot is removed, no auxin in available and shoot may stop growing
  • Extra auxin promotes growth in shoot but inhibits growth in root
• Phototropism:

  Exposure to light:

  • More auxin accumulates on side that's in shade than side exposed to light
  • Makes cell grow faster on shaded side so shoot bends towards light
• Geo/gravitropism:

  • When shoot is growing sideways, gravity produces unequal distribution of auxin on tip, with more auxin on lower side
  • Causes lower side to grow faster, bending shoot upwards
  • Root growing sideways will have more auxin on lower side
  • In root, extra auxin inhibits growth - cells on top elongate faster, and root bends downwards
• Gibberellin:

  • Stimulates seed germination, stem growth, flowering

  Used for:

  • Controlling dormancy - gibberellin can make plants germinate at the same time and in conditions they might not
  • Inducing flowering - gibberellin can make plants flower without change and grow bigger flowers
  • Growing larger fruit
• Ethene:

  • Influences growth by controlling cell division
  • Stimulates enzymes that causes fruit to ripen
  • Ripening can be delayed while the fruit is in storage by adding chemicals that block ethene's effect or reduce amount of ethene that fruit can produce
• Auxin is used to:

  • Kill weeds - disrupt normal growth patterns which kills weeds and leaving rest of plant untouched
  • Grow cuttings with rooting powder - cuttings can have rooting powder added to it to produce roots and allow farmers to produce clones
  • Grow cells in tissue culture - can stimulate growth medium to stimulate cells to divide to form both roots and shoots