Fig. 1.

The glucosinolate–myrosinase system in plant defense and as manipulated by the P. rapae NSP. In damaged plant tissue, glucosinolates (1) are hydrolyzed by myrosinases yielding glucose and unstable aglucones (2). (A) In mechanically damaged plant tissue, the aglucones rearrange spontaneously into isothiocyanates [mustard oils (3)], which have frequently been shown to act as insecticides. Depending on the structure of the glucosinolate side chain R and the reaction conditions, nitriles (4) and other hydrolysis products can also be formed. (B) In plant material ingested by P. rapae larvae, the aglucones (2) do not undergo the rearrangement to the toxic isothiocyanates (3) but instead form nitriles (4) caused by the presence of NSP.