Expert: David Haas - 9/27/2006

Question
As I understand it most cells in most plants are totipotent. This is
why grafts work. In humans and other animals I guess, very few
cells are totipotent. Skin cells produce skin cells only. Why? Is there
some evolutionary advantage to each organism from different
levels of totipotency? Also, what determines if a cell is totipotent or
not. Do you know of any books or journal articles that would
address this issue?

Answer
Theoretically all cells are totopotent. i.e. they all have a complete genome.  The thing is that as a multicellular organism develops certain sequences of genes are switched on and others off and the cells become differentiated into cells having specific functions.  

A large portion of a plant consists of cells that are not highly differentiated.  These are parenchyma cells which make up most of the soft tissues and are involved mostly in food manufacture and storage.  They are capable of dedifferentiation so that they can form other highly specialized tissues, even meristemetic cells which are capable of forming shoots and roots under the right circumstances.  

Plants are much simpler at the cellular level compared to animals.  It is like comparing the regenerative properties of simple animals that can regrow structures to mammals that can not. The fact that mammal cells have lost their regenerative properties may simply be due to their level of complexity.  Other factors would be more important than this ability as far as survival and reproduction.  Here is a web site that may help.

http://www.eppc.org/publications/pubID.2374/pub_detail.asp