Phytochrome
/ˈfaɪtoʊˌkroʊm/
Definition
Phytochrome is a light-sensing plant pigment protein, or photoreceptor, that detects red and far-red light. It helps plants measure light quality, day length, and shading from nearby plants by switching between two forms. This signaling system influences seed germination, stem elongation, leaf development, chlorophyll production, and flowering timing. Phytochrome occurs in many plants and helps coordinate growth with changing light conditions.
Role and Significance
- Light-quality sensing: Phytochrome helps plants compare red and far-red light, which changes across the day and under leaf shade. That signal guides decisions about when to germinate, elongate stems, or form leaves.
- Shade-avoidance response: In crowded plantings, a low red to far-red ratio can trigger taller, stretchier growth. This response helps a plant compete for light, but it can also lead to weaker, less compact form.
- Day-length timing: Phytochrome works with the plant’s internal clock to measure night length. This affects photoperiodic responses, meaning flowering or dormancy cues linked to seasonal changes in daylight.
- Seed and seedling establishment: Some seeds use phytochrome signals to detect whether light conditions are suitable for sprouting near the soil surface. In young seedlings, it also helps the shift from pale, elongated growth to greener, sturdier development after exposure to light.
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