Which of the following are fused in somatic hybridization involving two varieties of plants?

The correct answer is Protoplasts.

Step-by-Step Explanation:

1. Understanding Somatic Hybridization: Somatic hybridization is a cellular engineering technique where somatic (vegetative) cells from two different plant varieties or species are fused together to form a hybrid cell, which can then be regenerated into a new hybrid plant.

2. The Role of the Cell Wall: Plant cells are surrounded by a rigid cell wall composed of cellulose, hemicellulose, and pectin. This cell wall acts as a barrier that prevents the cell membranes of two different cells from coming into close contact and fusing.

3. Preparation of Protoplasts: To allow fusion to occur, the cell wall must first be removed. This is typically achieved by treating the plant tissues with cell-wall-degrading enzymes, specifically cellulase and pectinase. A plant cell whose cell wall has been completely removed is called a protoplast. Protoplasts are bound only by their plasma membranes.

4. Protoplast Fusion: Once the cell walls are removed, the naked protoplasts from the two different plant varieties can be brought together and induced to fuse. This fusion is facilitated using chemical agents (fusogens) like polyethylene glycol (PEG) or through electrical stimulation (electrofusion).

5. Conclusion: Therefore, it is the protoplasts of the two plant varieties that are directly fused during somatic hybridization.