Which combination of enzymes and substances is added sequentially to a sample of plant cells before the introduction of chilled ethanol during DNA isolation? 

The DNA should be in its pur form before it is subjected to restriction digestion.

Since the DNA is enclosed within the membranes, we have to break the cell open to release DNA along with other macromolecules such as RNA, proteins, polysaccharides and also lipids. This can be achieved by treating the plant tissue with the following enzymes.

Cellulase – cellulosic cell wall

 Protease  & RNase to remove proteins and RNA.