BRAINCAKEDiscovery
The pigment that detects light for flowering and germination is phytochrome. Its discovery came from experiments by Borthwick and Hendricks at the US Department of Agriculture in the 1950s.
They used lettuce seeds, which need light to germinate. Soaked seeds were exposed to flashes of light of different wavelengths. Red light (about 660 nm) stimulated germination. Far-red light (about 730 nm) inhibited it.
When seeds were given alternating flashes, the result depended only on the last flash:
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All 30 lessons in Chemical Control · All Edexcel A-level Biology topics