Photoperiodism

• Photoperiodims :

  Angiosperm = Flowering plants
• Flowering is an annual event for palnts - Occurs in response to change in Photo ( light ) periodism (24 hr length)
• Short day plants needs long night period

  This is where photoperiod is less than the CDL

  Seasons like Autumn , winter / Early Spring
• Long Day plants needs longer day - sunlight exposure

  This is where phtoperiod is greater than the CDL

  Seasons like Late Spring , Summer
• Day Neutral Plants flower independently of the photoperiod length

  Plants able to flower all year = tropics (Any time / Any season)
• 3 Types of Plants:

  Short day

  Long day

  Day neutral
• Phytochrome are light sensitive pigment which are present in leaves

  
• The ability to respond to photoperiodism is due to Phytochromes
• Phytochrome exist to two different Forms

  Pred / Pr and P far-red / Pfr

  Sunlight contains more Pr than Pfr
• During the day Pr rapidly convert to Pfr

  At night is a slow conversion back to Pr
• Slow conversion of Phytochromes acts as a clock

  If day is long enough - Pfr accumulates - long day plants flower Pr -> Pfr fast

  If night is long enough - Pr accumulates - Short day plants flowers Pr <- Pfr slow