Which one is required for protoplast fusion?

The somatic (protoplast) fusion process occurs in four steps:1. The removal of the cell wall of one cell of each type of plant using cellulase enzyme to produce a somatic cell called a protoplast2. The cells are then fused using either an electric shock (electrofusion) to join the cells and the nuclei fused together or by chemicaltreatment. The resulting fused nucleus is called heterokaryon.3. The somatic hybrid cell then has its cell wall induced to form using hormones4. The cells are then grown into calluses which then are further grown to plantlets and finally to a full plant, known as a somatic hybrid.