Auxins

Options

A. Were first isolated in agar by paal
B. Are synthesised using tryptophan as precursor
C. Are found always as bound with amines
D. Are synthesised in shoot apices only

Answer

### Step-by-Step Solution:

1. **Definition of Auxins**: Auxins are a class of plant hormones that play a crucial role in regulating plant growth and development.

2. **Synthesis Location**: Auxins are primarily synthesized in meristematic tissues, which are regions of active cell division. These tissues are found in:
- Shoot tips
- Root tips
- Flower buds
- Leaf tips

3. **Influence of Light**: The synthesis of auxins is influenced by light. They are produced more in the presence of light and less in the dark, indicating that light promotes auxin production.

4. **Precursor for Auxin Synthesis**: The primary auxin, indole-3-acetic acid (IAA), is synthesized from the amino acid tryptophan. This means that tryptophan serves as a precursor for auxin production.

5. **Evaluation of Statements**:
- **First Isolated in Agar**: This statement is incorrect as auxins were not first isolated in agar.
- **Synthesized Using Tryptophan as Precursor**: This statement is correct.
- **Found Always as Bound with Amines**: This statement is incorrect; auxins can exist in free forms as well.
- **Synthesized in Shoot Apices Only**: This statement is incorrect; auxins are synthesized in all areas of active growth, not just the shoot apices.

6. **Conclusion**: Based on the evaluation, the correct statement is that auxins are synthesized using tryptophan as a precursor.

### Final Answer:
The correct statement regarding auxins is: **They are synthesized using tryptophan as a precursor.**

---