Which of the following best shows that plant cells are totipotent?

The correct option is B Protoplast culture for the purpose of genetic engineering of plants
Totipotency is the ability of a single cell to divide and produce all the differentiated cells in an organism, including extraembryonic tissues. Protoplasts are naked plant cells without the cell wall, but they possess plasma membrane and all other cellular components. Protoplasts of different species can be fused to generate a hybrid and this process is referred to as somatic hybridization (or protoplast fusion). The protoplast in culture can be regenerated into a whole plant and its genetic transformations can be achieved through genetic engineering of protoplast DNA. This proves that totipotency is best shown in protoplast culture.

So the correct option is 'protoplast culture for the purpose of genetic engineering of plants'.