Salivary gland alpha-amylases retain activity in wheat grains damaged by Eurygaster (Heteroptera: Scutelleridae) Sunn bugs

Abstract

The Sunn pest Eurygaster integriceps and related wheat bugs (Sunn bugs) cause great damage to the wheat crop by injecting hydrolytic enzymes into the grain that liquefy the endosperm during extraintestinal digestion. The main harmful factor of bugs is considered to be their proteases, which are retained in the endosperm of damaged grain and flour and hydrolyze gluten proteins during dough kneading. Thus, the quality of bread deteriorates sharply. Salivary gland proteases provide protein nutrition for the wheat bugs. However, the main source of energy that allows them to accumulate fat necessary for wintering is the endosperm starch, hydrolyzed by alpha-amylases. Alpha-amylases of wheat bug salivary glands have not been sufficiently studied. There is still no consensus on the role of these enzymes in the nutrition of bugs, on their presence in damaged mature grain, and on their influence on the technological qualities of flour, which may be partly due to the lack of methods for detecting the actual bug alpha-amylases in grain. Using a new simple method, including inactivation of plant beta-amylases interfering with the analysis by sodium p-chloromercuribenzoate, we obtained alpha-amylase banding patterns similar to the patterns of wheat bug salivary gland alpha-amylases as a result of protein isoelectric focusing of some samples of damaged grain. The developed approach can be recommended for use in the technological assessment of damaged grain, in studying the mechanisms of plant immunity to pests as well as for diagnostics of grain damage by insects.