Apical dominance of root tip is probably due to

Options

A. Cytokinin
B. IAA-oxidase
C. Abscisic acid
D. Both B and C.

Answer

### Step-by-Step Solution:

1. **Understanding Apical Dominance**:
- Apical dominance refers to the phenomenon where the main central stem of the plant grows more vigorously than the side stems. This is primarily due to the influence of certain hormones.

2. **Identifying the Hormones Involved**:
- The question provides four options: Cytokinins, Indole Acetic Acid (IAA), Abscisic Acid (ABA), and a combination of B and C.

3. **Evaluating Cytokinins**:
- Cytokinins are known to promote cell division and are involved in lateral growth. They tend to promote lateral bud growth over apical growth, which means they do not support apical dominance. Thus, this option is incorrect.

4. **Evaluating Indole Acetic Acid (IAA)**:
- IAA is a natural form of auxin, which is a hormone responsible for promoting apical dominance. It encourages the growth of the main stem while inhibiting the growth of lateral buds. Therefore, this option is likely correct.

5. **Evaluating Abscisic Acid (ABA)**:
- ABA is known as the stress hormone and is involved in responses to stress conditions. It does not play a significant role in promoting apical dominance. Instead, it is more associated with processes like wound healing. Thus, this option is also incorrect.

6. **Conclusion**:
- Based on the evaluations, the correct answer to the question "Apical dominance of root tip is probably due to" is **Indole Acetic Acid (IAA)**.

### Final Answer:
**Indole Acetic Acid (IAA)**

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