(d) gene transfer without a vector
Explanation:
Polyethylene glycol method is used for gene transfer without a vector. Introduction of DNA into plant cells without the involvement of a biological agent and leading lo stable transformation is known as direct gene transfer. There are various methods for direct direct gene transfer, one of which ts chemical method. Certain chemicals, e.g. PEG (Polyethylene Glycol, polyvinyl alcohol and calcium phosphate enhance the uptake of DNA by plant protoplast. PEG and calcium phosphate are thought to precipitate the DNA onto the outer surface of plasmalemna and the precipitate is taken up by the endocytosis.
