BRAINCAKEPhytochromes, Photomorphogenesis and Tropisms
Phytochrome exists in two interconvertible forms:
Pr + red light (660 nm) → Pfr
Pfr + far-red light (730 nm) → Pr
Pfr → Pr slowly in darkness
Pfr + far-red light (730 nm) → Pr
Pfr → Pr slowly in darkness
Sunlight contains more red than far-red light, so in daylight Pfr accumulates. At night Pfr slowly converts back to Pr. Pfr is the physiologically active form: it causes de-etiolation, promotes germination and affects flowering. In long day plants Pfr promotes flowering; in short day plants it inhibits flowering, so they need long nights to let the Pfr level fall.
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Key terms in this lesson
- phytochrome
- A blue-green plant pigment existing in two interconvertible forms sensitive to red and far-red light, controlling responses such as flowering and germination.
- phototropism
- A growth response of a plant shoot or root towards or away from the direction of light.
More in Chemical Control
- Long Day Plants
- Short Day Plants
- Day Neutral Plants
- Signal Detection
- Discovery
- Photomorphogenesis
- Germination and Photomorphogenesis
- Phytochrome as a Transcription Factor
All 30 lessons in Chemical Control · All Edexcel A-level Biology topics