Re: what the biological significance is of potato having peroxidase ?

It is my understanding that the potato peroxidase/polyphenol oxidase are 
basically defensive in nature.  Wounding, either by a soil invertebrate, or 
invasion by a fungus, etc.  would lead to mixing of the enzymes (in the 
cytosol of the potato cells) with the phenolic substrates (stored in the 
vacuoles of the cells).  The resulting polyphenols and assorted free 
radicals would tend to kill the invaders.