Some seeds require light for germination. This process is controlled by the phytochrome system. Which of the following germination treatments would inhibit germination of such seeds?

• A. Exposure of seeds to only red light
• B. Far-red light followed by red light
• C. Green light followed by red light
• D. Red light and far-red light together, followed by red light only
• E. Exposure of seeds to red light followed by far-red light

Answer: (E)

Verified step by step guidance

1. Understand the role of phytochrome in seed germination: Phytochrome is a photoreceptor in plants that exists in two forms, Pr and Pfr. Pr absorbs red light and converts to Pfr, while Pfr absorbs far-red light and converts back to Pr. Pfr is the active form that promotes germination.
2. Identify the effect of red and far-red light: Red light converts Pr to Pfr, promoting germination. Far-red light converts Pfr back to Pr, inhibiting germination.
3. Analyze the treatments: Exposure to only red light will convert Pr to Pfr, promoting germination. Far-red light followed by red light will end with Pfr, promoting germination. Green light followed by red light will also end with Pfr, promoting germination.
4. Consider the treatment 'Red light and far-red light together, followed by red light only': This will result in a final state of Pfr, promoting germination.
5. Evaluate the treatment 'Exposure of seeds to red light followed by far-red light': This sequence ends with Pr, the inactive form, inhibiting germination.