Plant hormones

• Plants produce hormones to coordinate and control growth and responses to light and gravity.
• Tropism: Plant growth response to a stimulus.

  Phototropism: Plant growth response to light.

  Gravitropism/Geotropism: Plant growth response to gravity.

  Positive tropism: Towards the stimulus.

  Negative tropism: Away from the stimulus.

  Auxin: Plants hormone, it causes unequal growth rates in plant roots and shoots.
• Phototropism:

  Auxin produced at the tip of the shoot.

  Auxin moves to shaded side of the stem.

  Auxin causes cell elongation.

  
• Geotropism/Gravitropism:

  Auxin produced in the tip of the root and move to the size of the root that is toward gravity

  Auxins have opposite effect in the root compared to shoots

  In roots auxins stop cell elongation and roots grow down

  
• Gibberellins:

  Are involves in plant growth - they can cause dwarf plants to row to full size

  Overcome dormancy in seeds and initiate germination

  Used to end seed dormancy, promote flowering and increase fruit size
• Ethene:

  Controls cell division and ripening of fruits

  Helps flowers open

  Involved in the dropping of leaves from plants

  Rotting fruit gives off high concentrations of ethene

  Used in the food industry to control ripening of fruit during storage and transport
• Plants growth hormones are used in agriculture and horticuluture.
• Auxins are used:

  • as weed killers
  • as rooting powders
  • for promoting growth in tissue culture