Plant Hormones 2

• Hormones


  Chemical messengers synthesized at one location that deliver messages to a different location
• Five main types of hormones that influence plant growth

  • Auxin
  • Gibberellin
  • Cytokinin
  • Ethylene
  • Abscisic acid
• Auxin


  The hormone that allows plants to bend towards the light (phototropism)
• Auxin


  1. Synthesized at stem tips

  2. Travels downward

  3. Makes plant bend towards light by moving to shaded part of stem
• Gibberellins


  Important at several stages of plant development, required for germination, promote stem elongation
• Cytokinin


  Counters senescence, important in forming new plant organs (roots vs shoots)
• Cytokinin


  1. Produced in root apical meristem

  2. Passively carried up with water through xylem
• Ratio of auxin vs cytokinin


  Determines if plant forms roots or shoots
• Ethylene


  The 'magical ripening hormone', diffuses out of cells, produced by rapidly growing/dividing cells, inhibits leaf expansion
• Abscisic acid


  Signals dehydration, synthesized in chloroplasts of leaves, causes stomata to close to reduce water loss
• There are many more hormones that influence plant growth beyond the five main types discussed