____ and ____ show antagonistic effect in case of apical dominance but synergistic effect in case of differentiation :

Options

A. Cytokinin and Ethylene
B. Auxin and Cytokinin
C. Gibberellin and Cytokinin
D. ABA and Ethylene

Answer

To answer the question, "____ and ____ show antagonistic effect in case of apical dominance but synergistic effect in case of differentiation," we need to identify the two hormones involved in these processes.

### Step-by-Step Solution:

1. **Understanding Apical Dominance**:
- Apical dominance refers to the phenomenon where the main shoot (apical bud) of a plant grows more vigorously than the lateral buds. This is primarily regulated by hormones.

2. **Identifying the Hormones**:
- The two key hormones involved in apical dominance are **Auxin** and **Cytokinin**.
- **Auxin** promotes the growth of the apical bud while inhibiting the growth of lateral buds.
- **Cytokinin**, on the other hand, promotes the growth of lateral buds.

3. **Antagonistic Effect**:
- In the context of apical dominance, Auxin and Cytokinin have an antagonistic effect. Auxin promotes the growth of the apical shoot and inhibits lateral bud growth, while Cytokinin promotes lateral bud growth. Therefore, they work against each other in this scenario.

4. **Understanding Differentiation**:
- Differentiation is the process where meristematic tissues develop into specialized tissues. This process requires the cooperation of different hormones.

5. **Synergistic Effect**:
- During differentiation, Auxin and Cytokinin work together synergistically. They both promote the growth and development of cells as they transition from meristematic to permanent tissues.

6. **Final Answer**:
- Therefore, the two hormones that show an antagonistic effect in the case of apical dominance but a synergistic effect in the case of differentiation are **Auxin and Cytokinin**.

### Final Answer:
**Auxin and Cytokinin**