Studies on levels of glutathione S-transferase, its isolation and purification from Helicoverpa armigera

Helicoverpa armigera is a polyphagus pest of agricultural importance all over the world. In insects, glutathione S-transferase (GST) provides an important defence mechanism against plant allelochemicals as well as insecticides. The present work has been initiated in lepidoptern pest, H. armigera related to GST and its purification, characterization and endosulphan resistance. Spectrophotometrically, GST activity was measured and endosulphan bioassay was done with field-collected H. armigera at Akola Central India during August 1998 to March 2000. GST was detected in the eggs; it increased throughout the larval stages and was the highest in two-day-old fifth instar larva. On purification, maximum GST was found in the 70% ammonium sulphate fraction, while by affinity chromatography maximum activity was found in the bound fraction. Electrophoresis resolved only one isozyme having a molecular weight of 30 kDa. It was concluded that GST is responsible for endosulphan resistance, as GST levels and endosulphan resistance pattern were the same.