These articles give us some idea of the amount of research that has gone into determining how wheatgrass actually assists the "healing" of a broad spectrum of medical conditions and injuries.  Chlorophyll has been suggested, but there is no evidence that can support this theory.

Also, no chlorophyll exists in this wheatgrass extract I have used therapeutically, and highly effectively for treating a very broad spectrum of conditions, since 1995. Numerous biological activities are involved in the wheatgrass extract healing process - in particular, ligands influencing re-activation of dysfunctional cellular receptors and "re-connecting" them to the brain.

Dr. Chris Reynolds. M.B.,B.S.