BRAINCAKEGermination and Photomorphogenesis
Many small seeds, such as lettuce, need light to germinate. Small seeds have few food reserves, so a seedling that germinated deep in the soil or under other plants could run out of reserves before it reached the light.
Light-sensitive seeds contain phytochrome. When they absorb red light, Pr is converted into Pfr, the active form. Pfr triggers germination, partly by stimulating the synthesis of gibberellin (GA). Gibberellin switches on genes for enzymes such as amylase, which break down stored starch so the embryo can grow.
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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.
- etiolated
- Describes a seedling grown in darkness, with a long thin stem, small pale leaves and a hooked tip.
More in Chemical Control
- Long Day Plants
- Short Day Plants
- Day Neutral Plants
- Signal Detection
- Discovery
- Photomorphogenesis
- Phytochromes, Photomorphogenesis and Tropisms
- Phytochrome as a Transcription Factor
All 30 lessons in Chemical Control · All Edexcel A-level Biology topics