Photoperiodism Concepts

Photoperiodism

• Photoperiodism influences flowering in plants based on relative periods of light and darkness.
• Plants use hormones to respond to their environment, lacking a nervous system but exhibiting slow, sustained responses.

Plant Environmental Responses

• Light triggers phototropism, where shoots grow towards it.
• Photoperiodism allows plants to respond to light and dark periods, influencing flowering.

Monitoring Day Length

• Plants monitor day length using photoreceptors called phytochrome.
• Phytochrome absorbs specific wavelengths, specifically blue/green light, and exists in two inter-convertible forms: Pr and Pfr.

Phytochrome Forms

• Pr (phytochrome absorbing red light at 600nm) is dominant during daylight.
• Pfr (phytochrome absorbing far red light at 730nm) is predominant during the night.

Day and Night Phytochrome Dynamics

• During the day, Pr converts to Pfr rapidly.
• At night, Pfr converts back to Pr slowly, resulting in accumulation of Pr.

Light Detection and Flowering

• Light is detected in the leaves, with the stimulus transmitted to buds for flowering.
• Flowering is initiated by the hormone florigen.
• Day length is crucial for plant flowering responses.

Groups of Flowering Plants

• Flowering plants are categorized into three groups:
  • Day Neutral Plants: Flowering unaffected by day length (e.g., cotton, tomato, cucumber).
  • Long Day Plants: Require longer light periods, shorter darkness (e.g., cabbage, petunia).
  • Short Day Plants: Require shorter light periods, longer darkness (e.g., tobacco, poinsettia).

Flowering Conditions

• Short day plants can only flower in darkness; interruptions by light prevent flowering.
• Long day plants can only flower in light; interruptions by darkness promote flowering.