Contents - Faperta

226 Biotechnological Approaches for Pest Management and Ecological Sustainability
inhibitors for insect control requires a detailed analysis of particular insect-plant interaction.
The ability of some insect species to compensate for protease inhibition by switching
to an alternative proteolytic activity or overproducing the existing proteases may limit the
application of protease inhibitors in such species ( Jongsma et al., 1995). Adaptive mechanisms
elevate the levels of other classes of proteinases to compensate for the trypsin activity
inhibited by dietary proteinase inhibitors.
Soybean Kunitz type trypsin inhibitor (SBTI) and soybean Bowman-Birk type trypsinchymotrypsin
inhibitor (SBBI) reduced the larval weight of H. armigera, and such effects
were greater for SBTI than SBBI (Johnston, Gatehouse, and Anstee, 1993; Shukla, Arora,
and Sharma, 2005). Larvae feeding on diet containing 0.234 mM SBTI also reduced the
trypsin-like enzyme activity in the gut of H. armigera. There is considerable diversity in
protease inhibitors of cultivated chickpea and its wild relatives (Patankar et al., 1999). The
diversity in proteinase activity in H. armigera gut and the fl exibility in their expression
during developmental stages depending on the diet provides a basis for selection of proper
PIs for use in transgenic plants (Patankar et al., 2001). Helicoverpa armigera fed on chickpea
showed more than 2.5- to 3-fold proteinase activity than those fed on pigeonpea, and cotton.
Over 90% of the gut proteinase activity of the fi fth-instar larvae is of the serine proteinase
type, while the second-instar larvae showed the presence of metalloproteases, aspartic-,
cysteine-, and serine-proteinases. Proteinase inhibitors with multi-inhibitory activities
were generated by replacement of phytocystatin domains in sunfl ower multi-cystatin
(SMC) by the serine proteinase inhibitor BGIT from bitter gourd, Momordica charantia L.
seeds. Inanaga et al. (2001) compared the chimaeric inhibitors and the recombinant SMC
(r-SMC) in relation to their effects on the growth of S. exigua larvae. When the second
instar larvae were reared on a diet containing rSMC, SMC-T3, or SMC-T23 for ten days,
a signifi cant reduction in weight gain was observed (Inanaga et al., 2001). Mean weights
of larvae with rSMC, SMC-T3, and SMC-T23 diets were 43, 32, and 43 mg, respectively,
compared to 60 mg in the control diet. In contrast, BGIT had little effect on the growth of
the S. exigua larvae. The results suggested that SMC-T3 with two phytocystatin domains
and one serine proteinase inhibitor domain is an effi cient inhibitor of proteinases in
S. exigua larvae (Inanaga et al., 2001). Considerable progress has been made in deploying
proteinase inhibitors in transgenic plants for controlling various insect pests (Table 7.3).
Tobacco
Transgenic tobacco plants expressing cowpea trypsin inhibitor (CpTi) have shown resistance
to H. armigera (F.P. Zhang et al., 1998). Transgenic tobacco plants expressing high
levels of SBTI have shown greater resistance than the tobacco plants expressing CpTi
against H. virescens. The SBTI is also more effective than CpTi in reducing the proteolytic
activity of gut extracts obtained from full-grown larvae of H. armigera. Proteolysis by gut
extracts showed 40-fold more inhibition by SBTI than CpTi (Gatehouse et al., 1993).
However, CpTi is considered to be more useful for genetic transformation, because unlike
many serine protease inhibitors (SPIs), it is not deleterious to mammals (Pusztai et al.,
1992). In another study, H. armigera larvae fed on transgenic tobacco plants expressing
SBTI gene showed normal growth and development (Nandi et al., 1999). In another study,
transgenic tobacco plants expressing SBTI resulted in increased insect mortality, reduced
insect growth, and reduced plant damage by H. virescens (Hilder et al., 1987), H. zea
(Hoffman et al., 1992), Spodoptera littoralis (Boisd.), M. sexta (Yeh et al., 1997; McManus
et al., 1999), and H. armigera (Charity et al., 1999). Helicoverpa armigera larvae fed on
plants expressing the giant taro, Alocasia macrorrhiza (L.) G. Don proteinase inhibitor