The phytohormone combination which is the key regulator of cell differentiation and morphogenesis is

Options

A. Cytokinin and IAA
B. IAA and ABA
C. IAA and `GA_(3)`
D. Cytokinin and gibberellin

Answer

To solve the question regarding the key regulator of cell differentiation and morphogenesis in plants, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the combination of phytohormones that regulates cell differentiation and morphogenesis in plants.

2. **Identifying Key Terms**:
- **Phytohormones**: These are plant hormones that regulate various aspects of growth and development.
- **Cell Differentiation**: This is the process by which cells become specialized in structure and function.
- **Morphogenesis**: This refers to the biological process that causes an organism to develop its shape.

3. **Analyzing the Options**: The options provided are:
- Cytokinin and IAA (Indole Acetic Acid)
- IAA and ABA (Abscisic Acid)
- IAA and GA3 (Gibberellin)
- Cytokinin and Gibberellin

4. **Understanding the Role of Each Hormone**:
- **IAA (Indole Acetic Acid)**: A type of auxin that promotes root formation and is crucial for cell elongation and differentiation.
- **Cytokinin**: Promotes cell division and is essential for shoot development.
- **ABA (Abscisic Acid)**: Primarily involved in stress responses and does not play a significant role in differentiation and morphogenesis.
- **GA3 (Gibberellin)**: Involved in stem elongation and seed germination but not primarily in differentiation and morphogenesis.

5. **Combining the Hormones**:
- The combination of **Cytokinin and IAA** is known to promote both cell division (via cytokinin) and differentiation (via IAA), leading to the formation of roots and shoots from an undifferentiated mass of cells (callus).

6. **Conclusion**: Based on the analysis, the correct answer is **Cytokinin and IAA**.

### Answer:
The phytohormone combination which is the key regulator of cell differentiation and morphogenesis is **Cytokinin and IAA (Indole Acetic Acid)**.

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