thuringiensis (Bt) is highly toxic to the larvae of the
tomato fruit borer, Helicoverpa armigera (Chakrabarti
et al., 1998). In the present study, a synthetic cry1Ac gene
modi"ed for plant codon usage and having a G#C
content of 47.7% was selected for introduction into
tomato (Sardana et al., 1996). A. tumefaciens strain LBA
4404 carrying pBinBt3 was used to transform tomato
cotyledonary explants, and 43 plantlets resistant to
kanamycin were regenerated. The e$ciency of transformation
was 8%. Polymerase chain reaction (PCR)
analysis of genomic DNAs from the regenerated plantlets
using primers for nptII gene revealed that all the plants
were putative transformants (data not shown). Preliminary
insect bioassays with the leaves of the transgenic
plants using second instar larvae of Helicoverpa armigera
revealed high levels of protection in seven out of 43
plants. All subsequent experiments were performed with
these seven plants and their progeny. Genomic DNA
samples from six of these plants were digested with HindIII
and Southern hybridized (Fig. 2). HindIII cuts only
within the T-DNA (Fig. 1), just downstream of the Octopine
synthase-poly (A) sequence and so provided information
regarding the insertion position and number
of the transgene copies. The results demonstrated the
presence of more than one copy in all the transgenic