Auxin can be bioassayed by

Options

A. avena coleoptile curvature
B. hydroponics
C. potometer
D. lettuce hypocotyl elongation

Answer

### Step-by-Step Solution:

1. **Understanding Auxin**: Auxins are a class of plant hormones that play a crucial role in regulating plant growth and development. They are involved in processes such as cell elongation, root formation, and fruit development.

2. **Bioassay Definition**: A bioassay is a scientific experiment that determines the concentration or potency of a substance by its effect on living cells or tissues. In the case of auxins, specific tests can be used to measure their activity.

3. **Identifying the Options**:
- **Option A: Avena coleoptile curvature**: This test involves using the coleoptile (the protective sheath covering the emerging shoot) of the oat plant (Avena sativa) to measure the curvature response to auxin. When auxin is applied to one side of the coleoptile, it causes that side to elongate more than the other, resulting in curvature towards the side without auxin.
- **Option B: Hydroponics**: This is a method of growing plants in a nutrient solution without soil. It does not specifically measure auxin activity.
- **Option C: Potometer**: A potometer is an instrument used to measure the rate of water uptake in plants, which is not directly related to auxin bioassay.
- **Option D: Lettuce hypocotyl elongation**: This test is used to measure the effects of gibberellins, another type of plant hormone, rather than auxins.

4. **Conclusion**: Based on the information above, the correct method to bioassay auxin is through the Avena coleoptile curvature test. Therefore, the answer is **Option A**.

### Final Answer:
Auxin can be bioassayed by **Avena coleoptile curvature** (Option A).

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