Plant hormones

• Plant hormones= chemical molecule that are made in one part of the plant and travel to target cells in another part.
• Gibberellins

  = Help with seed germination

  • They switch on genes which code for enzymes- amylase, protease. Food stores in seeds are digested to provide ATP for growth.
  • Seeds without gibberellins don't germinate, if gibberellins are added then seeds germinate.
  • Also increase the length of internodes- grow taller.
  • If gibberellins pathway is disrupted, plants have shorter stems.
• Commerial uses of gibberellins

  • Can delay ripening
  • Improve size and shape of fruit.
• Auxins

  = Promote cell elongation.

  • They maintain plasticity of cell walls in shoots and roots.
  • Causes apical dominance.
  • When the tip of the plant is cut there is more lateral growth.
  • Higher concentration of auxin can inhibit growth.
• Commercial uses of auxins

  • Rooting powder
  • Weedkiller
  • Produce seedless fruit.
• Ethene

  = Cause fruit ripening

  • Promotes abscission in deciduous trees.
  • Promote fruit dropping
  • Fruit ripening after they are harvested.
• ABA

  = Maintain dormancy of seeds and buds

  • Stimulates cold protective responses- antifreeze
  • Stimulate stomatal closing
• Cytokinins

  • Prevent ageing in ripened fruit