If seeds are exposed to red light 600 nm and far red light 730, which light if given last can bring seed germination?

Answer

To determine which light, when given last, can bring about seed germination after exposure to red light (600 nm) and far red light (730 nm), we can analyze the effects of these light wavelengths on seed germination.

### Step-by-Step Solution:

1. **Understand the Role of Light Wavelengths**:
- Red light (600 nm) is known to promote seed germination.
- Far red light (730 nm) has an inhibitory effect on seed germination.

2. **Initial Exposure**:
- The seeds are first exposed to red light (600 nm). This exposure is beneficial and promotes germination.

3. **Subsequent Exposure**:
- If the seeds are then exposed to far red light (730 nm), this light will inhibit the germination process. Far red light inactivates phytochrome photoreceptors, which are crucial for the germination process.

4. **Effects of Phytochrome**:
- Phytochromes are light receptors in plants that help regulate various processes, including seed germination. When inactivated by far red light, the levels of gibberellins (GA) decrease, while abscisic acid (ABA) levels increase. ABA promotes dormancy, which prevents germination.

5. **Final Light Exposure**:
- To counteract the inhibitory effects of far red light, the last light exposure should be red light (600 nm). This will reactivate the phytochrome photoreceptors and promote germination.

6. **Conclusion**:
- Therefore, if seeds are exposed to red light first and then far red light, the last light exposure that can bring about seed germination is red light (600 nm).

### Final Answer:
**Red light (600 nm) should be given last to promote seed germination.**

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