is the first mentioned compound found in any other plants?
Yes, in mustard, cabbage, and horseradish.
Glucosinolate
Glucosinolates are natural components of many pungent plants such as mustard, cabbage, and horseradish.
when did radishes become a food source for humans They were domesticated in Asia prior to Roman times. how are they consumed? They are mostly eaten raw as a crunchy salad vegetable with bite. are there other varieties? Yes, they differ based on the  seasons when they are grown and a variety of shapes, lengths, colors, and sizes, such as red, pink, white, gray-black, or yellow radishes, with round or elongated roots that can grow longer than a parsnip. what are parsnips? It is a root vegetable closely related to carrot and parsley; all belong to the family Apiaceae. what chemical compound give the first mentioned root vegetable its sharp taste? Glucosinolate, myrosinase, and isothiocyanate
wiki:18404989
Glucosinolate [SEP] Introduction
Glucosinolates are natural components of many pungent plants such as mustard, cabbage, and horseradish. The pungency of those plants is due to mustard oils produced from glucosinolates when the plant material is chewed, cut, or otherwise damaged. These natural chemicals most likely contribute to plant defence against pests and diseases, and impart a characteristic bitter flavor property of cruciferous vegetables.