The impact of ingested potato type II inhibitors on the production of the major serine proteases in the gut of Helicoverpa armigera

The flowers of the ornamental tobacco produce high levels of a series of 6 kDa serine protease inhibitors (NaPIs) that are effective inhibitors of trypsins and chymotrypsins from lepidopteran species. These inhibitors have a negative impact on the growth and development of lepidopteran larvae and have a potential role in plant protection. Here we investigate the effect of NaPIs on the activity and levels of serine proteases in the gut of Helicoverpa armigera larvae and explore the adaptive mechanisms larvae employ to overcome the negative effects of NaPIs in the diet. Polyclonal antibodies were raised against a Helicoverpa punctigera trypsin that is a target for NaPIs and two H. punctigera chymotrypsins; one that is resistant and one that is susceptible to inhibition by NaPIs. The antibodies were used to optimize procedures for extraction of proteases for immunoblot analysis and to assess the effect of NaPIs on the relative levels of the proteases in the gut and frass. We discovered that consumption of NaPIs did not lead to over-production of trypsins or chymotrypsins but did result in excessive loss of proteases to the frass.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (114 K)Download as PowerPoint slideHighlights► Antibodies were made against the major trypsins and chymotrypsins from Helicoverpa punctigera larvae. ► We used the antibodies to optimize procedures for extraction of proteases for immunoblot analysis and activity assays. ► Consumption of proteinase inhibitors did not lead to overproduction of trypsin or chymotrypsin. ► Ingestion of proteinase inhibitors resulted in excessive loss of proteases in the frass.