Plant hormones

• Hormones act locally in plants.
• Auxins;

  • Controls growth at the end of shoots and roots.
  • Once produced at tips, they disolve in the solution of cells, and diffuse backwards along the shoots and roots.
  • In SHOOTS they stimulate growth, while the ROOTS they inhibit growth.
  • Once auxins are produced and dissolved they'll accumulate on the shaded side for shoots and on the lower side for roots.
• Auxins in roots :

  • Negatively phototropic (growing away from light)
  • {If roots detect light, auxins will accumulate on shaded side and inhibit growth, so sunny side will grow faster and more elongated cells, which will result in roots growing away from light .}
  • Positively geotropic (growing towards the ground)
  • {Auxins accumulate on the lower side and inhibit growth, so the upper side will grow faster and more elongated cells, therefore resulting in growing towards the ground.}
• Uses of auxins;

  • Growing plant clones - {from plant cells in tissue culture, by adding a growth medium with auxins and other nutrients.}
  • Growing plants from cuttings - {planting cuttings in soil with growing powder, which contains auxins.}
  • Kill weeds - {by adding lots of auxins which distrubs growth pattern, therefore killing plant. Also selective weed killers can be developed as most weeds are broad-leaved plants. }
• Auxins in shoots :

  • Positively phototropic (growing towards light)
  • {Auxins gather on the shaded side and stimulate growth on that side only. So shaded side will have more elongated cells and fatser growth, therefore shoots will grow towards the light.}
  • Negatively geotropic (growing away from ground)
  • {Auxins gather on lower side and stimulate growth on that side, making elongated cells with quicker growth. Therefore shoot will grow away from the ground.}

  
• Uses of Gibberellin:

  • Controlling dormancy - {farmers can induce germanation when the conditions aren't perfect, so multiple crops a year can be grow.}
  • Inducing flowering - {inducing flowering when certain conditions aren't met, and can make more and bigger flowers.}
  • Growing larger fruit - {used for plants which are seedless, as they don't grow as big.}
• Use of ethene:

  • Used to stimulate ripening of fruit.
  • When food is shipped it's picked before it's ripe, so when it arrives it's given ethene to ripen.
  • However, fruits produce their own ethene, so while being shipped the production of ethene is blocked.
  • Ethene works by stimulating an enzyme which causes fruit to ripen.
• Tropism - the growth response of a plant towards stimulus, such as a light, gravity or water.