control of flowering

Question 1

What are the external and internal factors that control flowering in plants?

Answer 1

-External Factors:
Photoperiod: The length of day and night determines flowering in some plants.
Cold: Exposure to cold temperatures can trigger flowering (e.g., vernalization).
- Internal Factors:
Circadian Biological Clock: Internal rhythms that influence timing.
Growth and Age: Plants must reach a certain size and age before flowering.
Gibberellins: Plant hormones that promote flowering.
Autonomous Pathway: Internal mechanisms that regulate flowering independent of external cues.

Question 2

How is flowering initiated in plants?

Answer 2

• The plant undergoes a developmental switch from vegetative to reproductive growth.
• The shoot apical meristem (SAM) stops producing leaves and starts producing floral organs.
• This switch occurs when the plant receives signals indicating it is ready to flower, typically when it has reached a certain size and age, and environmental conditions (temperature, photoperiod) are favorable.

Question 3

What are the key developmental stages controlling flowering?

Answer 3

1) Growth: The plant must grow to a sufficient size.
2) Differentiation: The plant must reach a certain developmental stage (vegetative) before flowering.
3) Life Cycle Types:
- Annual plants: Flower, produce seeds, and die in one year.
- Biennial plants: Flower in the second year after growth.
- Perennial plants: Live for more than two years, flowering annually or at intervals.

Question 4

What are the different responses to photoperiod in plants?

Answer 4

• Long Day (LD) Plants: Flower in spring or early summer when days are long.
• Short Day (SD) Plants: Flower in late summer or autumn when nights are long.
• Day Neutral Plants: Flowering is controlled by factors like age and temperature rather than photoperiod.
• Critical Night Length: Both LD and SD plants rely on the length of the night to determine flowering.

Question 5

What photoreceptors help plants sense light and control flowering?

Answer 5

• Cryptochrome: Absorbs blue light, mainly in the morning, and regulates the plant’s internal clock.
• Phytochrome: Absorbs red and far-red light during the day, influencing flowering.
• Phytochrome forms:
  Pr (inactive form) and Pfr (active form).
  Pfr promotes flowering in long day plants and inhibits flowering in short day plants.

Question 6

What is Florigen, and how does it regulate flowering?

Answer 6

• Florigen (FT): A protein that triggers flowering, produced in the leaves and transported to the shoot apical meristem (SAM).
• FT does not bind directly to DNA; it binds to a transcription factor called FD, and the FT-FD complex regulates flowering genes.
• TSF (Twin Sister of FT) is a close relative of FT that also plays a role in flowering.
• Anti-Florigen:
  BFT (Brother of FT) and TFL1 (Terminal Flower 1) act as inhibitors of flowering.
  TFL1 specifically maintains the inflorescence meristem (IM) and prevents premature floral development.