Infestation by cabbage aphid (Brevicoryne brassicae) on oilseed rape (Brassica napus) causes a long lasting induction of the myrosinase system

Cabbage aphid, Brevicoryne brassicae ( L.) ( Hemiptera: Aphididae), is specialised on cruciferous plants and constitutes a world-wide problem with a substantial negative impact on agriculture and horticulture. The myrosinase- glucosinolate system present in crucifers is believed to serve as an important barrier to general herbivores, whereas specialist insects rely on this system for host recognition. Two proteins with unknown function, myrosinase binding protein (MBP) and myrosinase associated protein ( MyAP), are also present in such plants and bind to specific myrosinases. In order to study regulation and overall effects on the myrosinase system, one leaf of oilseed rape ( Brassica napus L.) ( Brassicaceae) plants at the two-leaf stage was exposed to cabbage aphids for 1 h. After removal of the insects, infested and non-infested leaves were analysed by Northern blot analysis for the presence of MBP, MyAP, and myrosinase transcripts at different time points up to 48 h. MBP transcript levels continued to rise during the whole experiment, and were seven-to eight-fold higher compared with control plants 48 h after removal of the aphids. At 24 h the MyAP transcripts reached maximal levels and were four-fold higher than the control levels. Myrosinase transcripts were down regulated by aphid infestation and the level was less than half that of the control plants at 48 h. Apparently cabbage aphid infestation causes both transient and more long lasting ( up to 48 h) effects on the myrosinase system of the host.