In vivo and in vitro effect of Acacia nilotica seed proteinase inhibitors on Helicoverpa armigera (Hübner) larvae.

Acacia nilotica proteinase inhibitor (AnPI) was isolated by ammonium sulphate precipitation followed by chromatography on DEAE-Sephadex A-25 and resulted in a purification of 10.68-fold with a 19.5% yield. Electrophoretic analysis of purified AnPI protein resolved into a single band with molecular weight of approximately 18.6+1.00 kDa. AnPI had high stability at different pH values (2.0 to 10.0) except at pH 5.0 and are thermolabile beyond 80°C for 10 min. AnPI exhibited effective against total proteolytic activity and trypsin-like activity, but did not show any inhibitory effect on chymotrypsin activity of midgut of Helicoverpa armigera. The inhibition kinetics studies against H. armigera gut trypsin are of non-competitive type. AnPI had low affinity for H. armigera gut trypsin when compared to SBTI. The partially purified and purified PI proteins-incorporated test diets showed significant reduction in mean larval and pupal weight of H. armigera. The results provide important clues in designing strategies by using the proteinase inhibitors (PIs) from the A. nilotica that can be expressed in genetically engineered plants to confer resistance to H. armigera.

DNA synthesis in the imaginal wing discs of the American bollworm Helicoverpa armigera (Hübner).

The effect of two insect growth regulators of plant origin viz. plumbagin and azadirachtin and the ecdysteroids 20-hydroxyecdysone, makisterone A and a phytoecdysteroid on DNA synthesis in imaginal wing discs of day 4 final instar Helicoverpa armigera larvae was studied. DNA synthesis increased with increase in time of incubation up to 8 h and decreased later without the addition of moulting hormone. Addition of 20-hydroxyecdysone supported long term acquisition of competence for DNA synthesis in the wing discs. Both DNA synthesis and protein content were drastically reduced in plumbagin and azadirachtin-treated insects. Under in vitro conditions, plumbagin had a more pronounced inhibitory effect than azadirachtin. All the ecdysteroids tested, viz. makisterone A, 20-hydroxyecdysone and the ecdysteroidal fraction from the silver fern Cheilanthes farinosa enhanced DNA synthesis.