control of flowering

-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.

• 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.

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.

• 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.

• 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.

• 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.