Diamond-back moth ( Plutella xylostella ) is a serious insect pest specialised for herbivory on Crucifers although such plants contains the glucosinolate–myrosinase system implied as an important resource to withstand insect pests. We have compared the effects of mechanical wounding using forceps or scissors with herbivory by diamond-back moth larvae on oilseed rape ( Brassica napus ). The transcript levels of myrosinase binding protein (MBP), myrosinase associated protein (MyAP) and myrosinase were studied of leaf samples at different time points together with myrosinase enzyme activity measurements. In all cases, wounding gave a transient local increase in transcript levels of MBP and MyAP that were similar to control levels again within 24–48 h. Systemic induction of MBP and MyAP transcripts was observed after diamond-back moth herbivory and mechanical wounding by scissors while wounding by forceps caused down-regulation. In contrast, the myrosinase transcript levels were induced less and in wounded leaves after diamond-back moth feeding only. The myrosinase activity decreased especially in the soluble fraction prepared from wounded leaves after herbivory. The changes in MBP and myrosinase transcript levels were reflected in protein levels according to Western blot analysis. Mechanical wounding with forceps is often used for convenience as a substitute for insect attack but does not mimic well the effects of diamond-back moth herbivory to the plants.
