Colorado potato beetles ( leptinotarsa decemlineata) adapt to proteinase inhibitors induced in potato leaves by methyl jasmonate

Abstract

Potato plants were treated with gaseous methyl jasmonate (MJ) to obtain leaves with high induced levels of cysteine and aspartic proteinase inhibitors. Induced papain inhibitor activity was estimated at 4% of total protein. Other conditions produced leaves with low and moderate levels of this inhibitor. Development of Colorado potato beetle larvae was similar when they were reared on leaves containing low, moderate and high levels of papain inhibitor. Nevertheless, general proteinase activity was significantly reduced (42%) in insects reared on the high inhibitor diet, while proteinase activity that was insensitive to induced inhibitors in juice from MJ-treated leaves had increased two-fold. Activities towards the specific cysteine proteinase substrate p-Glu-Phe-Leu- pNA were the same in guts from insects reared on the three leaf types. However, juice from MJ-treated leaves inhibited as much as 67% of this activity in guts of insects reared on the low inhibitor diet compared to only 27% of the activity in gut extracts from insects reared on MJ-treated leaves, indicating a 2.5-fold induction of cysteine proteinase activity insensitive to potato proteinase inhibitors. None of the activities towards another specific cysteine proteinase substrate l-Arg- pNA were sensitive to inhibitors from MJ-treated leaves, but guts of insects fed these leaves had a 3.5-fold induction of this proteinase activity compared to those reared on plants containing low papain inhibitor levels. These data suggest that Colorado potato beetle larvae compensated for inhibited gut proteolytic activity during chronic intake of papain inhibitors by synthesizing insensitive proteinase(s).