The Gemara in Shabbos states that it is forbidden to put salt on radish. However, if it is only one piece of radish and it will be eaten immediately it is permitted. It is also clear from the Gemara that it is not limited to radish but rather includes other similar types of vegetables.
There is debate as to the nature of the prohibition. Some suggest that it is similar to working on animal hides where a process similar to slating was used to toughen the hide. Others suggest that placing salt on these vegetables is a form of pickling which is similar to cooking.
We will discuss the practical ramifications in the days to come.