High concentration of auxin is present in

Options

A. root apex
B. stem apex
C. node
D. petiole

Explanation

**Step-by-Step Solution:**

1. **Understanding Auxin**: Auxin is a type of plant hormone that plays a crucial role in regulating plant growth and development. It is known for its involvement in various processes such as cell elongation, root formation, and apical dominance.

2. **Location of High Concentration**: Auxin is found in higher concentrations at specific parts of the plant. The question asks where the high concentration of auxin is present.

3. **Evaluating Options**:
- **Root Apex**: While auxin is present here, it is not the area of highest concentration.
- **Stem Apex**: This is the tip of the stem where auxin is known to be present in high concentrations. It promotes stem elongation and apical dominance.
- **Node**: Nodes are points on the stem where leaves are attached, but they do not have high concentrations of auxin.
- **Pituitary**: This is a gland in animals, not a part of plants, and thus irrelevant to the question.

4. **Conclusion**: Based on the evaluation, the area with the highest concentration of auxin is the stem apex. This high concentration is essential for promoting growth and inhibiting lateral bud development, leading to apical dominance.

5. **Final Answer**: The correct answer is the **stem apex**.

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