Photoperiodism

Rucete ✏ Biology In a Nutshell

1. What Is Photoperiodism?

Photoperiodism is the response of plants to changes in the length of day and night (photoperiod).
It regulates flowering and other developmental processes.

2. Types of Plants Based on Photoperiod Response

a) Long-Day Plants

• Flower in the spring and early summer when daylight is increasing

b) Short-Day Plants

• Flower in the late summer and early fall when daylight is decreasing

c) Day-Neutral Plants

• Do not depend on day length to flower
• Flowering is independent of photoperiod

3. Role of Phytochrome System

• Phytochrome is a light-sensitive pigment involved in photoperiod detection
• Exists in two interconvertible forms:
  • Pr: absorbs red light (660 nm)
  • Pfr: absorbs far-red light (730 nm)
• Red light converts Pr to Pfr (active form)
• In darkness, Pfr slowly reverts to Pr

4. Florigen

• A hypothetical flowering hormone called florigen is thought to be produced in leaves
• Believed to travel to the shoot apex to trigger flowering