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loss of toxin activity (Uaw~thya et al., 1998). W~tll reference to cytosolic (Cyt) toxins Cyt
1Aa was studied ill detail. It was found tllnt plasma membrane liposonles contain~ng
phospholipids arc the target of this loxi11 (Tl~onlas ilnd Ellnr, 1983). Tox~n binding leads to
a deterge~~t-l~ke rsarraligenieilr of the bound I~pids, re,ult~ng in hypcrtroplly disruptio~t of
the membrane ~ntegrity and eventually cytolys~s. I'ore ibrmatio~l was observed prior to
cytolys~s (Gill st al., 1992). The 24 kDA active toxi11 \+as lbund to be three times actlve
tlla~l the protoxin (Butko ct al., 1996). Anotllcr ~nlcrest~ilg aspect of the ~ilode of:~c[~o~~ 1s
that thc tux111 monolllrrs display a synel-gist~c aclio11 towards spec~fic i~isecls. D~ffcrc~~t
synerg~st~cally exert~ng some host specific action (Crickmore et al.. 1995) and tllis ,was
dcmonatl.;lted by cloning a conlbinatlon of cry 4A and cry I IA of Bti into E.coli (Ben-Uov
CI :I\., 1995).
2.3.2.2 Genes employed l'or illsect resislancc otller t11a11 Bt:
Protease Inllibitors:
The p~.oduction of transgenic crops has seen rapid c~dvnnces during the last decade w11h the
commerc~al ~ntroductio~i of Br tra~isgenics However, the n~ajor concern with tllese crops
has been the developmellt of resistance by pest and public acceptabil~ty, Hence, there has
been a need to discover new effective plant genes, which would offer resistance and
protectio~l against these pests. Protease i~ihibitora (Pls) are one of the pritne candidates
with highly proven inllibitory acrivity against insect pests.
Pla111 proteitse bshibilors: Tlle possible role of protease inh~bitors (Pls) In plaill
protection was investigated as early as 1947 when, Mlckel and Stand~sll observed that the