Phytocromes

• What are phytocromes?

  . Photoreceptors

  . That absorb light

  . In leaves, seeds, roots, stem
• What are the two types of phytocromes?

  Pr

  Pfr

  Photoreversible conversion
• What are the quick conversions?

  Pr -> Pfr in red light

  Pfr -> Pr in far red light
• What are the slow conversions?

  Pfr -> Pr in far red light at night time
• What evidence do we have that Pfr is the active form of phytocromes?

  . Flashes of red light on plant

  . Triggers germination

  . As Pr -> Pfr
• Whats a photo-period?

  Minimum amount of light needed for flowering
• How does Pfr regulate transcription of genes?

  . Pfr can bind directly to DNA & act as a transcription factor

  OR

  . Pfr can activate other proteins that can act as a transcription factor
• What are other functions of IAA?

  1. Inhibits growth of side branches - apical dominance
  2. Stimulates lateral root growth
  3. Stimulates fruit development
  4. Involved in leaf fall
• What can synthetic IAA do?

  1. Act as weedkillers
  2. Induce fruiting
  3. Initiate rooting of cuttings (downward growth of roots) - e.g. you get get a stem of flower, plant it, and grow another flower