In plant biotechnology , PEG is used in:

Options

A. Protoplast isolation
B. Cell culture preparation
C. Protoplast fusion
D. Hardening

Answer

### Step-by-Step Solution:

1. **Understanding PEG**: The first step is to identify what PEG stands for. PEG is an abbreviation for polyethylene glycol. It is a polymer that has various applications in biotechnology.

2. **Identifying Uses of PEG**: In plant biotechnology, PEG is primarily used in several processes. We need to evaluate the options provided in the question to determine its specific application.

3. **Evaluating the Options**:
- **Option 1: Protoplast Isolation**: This process involves the removal of the cell wall from plant cells, but PEG is not primarily used for this purpose.
- **Option 2: Cell Culture Preparation**: While PEG can be involved in some aspects of cell culture, it is not its main application.
- **Option 3: Protoplast Fusion**: This is the process where two protoplasts (cells without cell walls) are fused together. PEG is commonly used in this process as it facilitates the fusion of protoplasts by promoting membrane fusion.
- **Option 4: Hardening**: This refers to the acclimatization of tissue-cultured plants to external conditions, and PEG is not used in this process.

4. **Conclusion**: Based on the evaluation of the options, the correct answer is **protoplast fusion** (Option 3), as PEG is specifically utilized to enhance the fusion of protoplasts in plant biotechnology.

### Final Answer:
In plant biotechnology, PEG is used in **protoplast fusion**.