Abstract
An organ culture system derived from Helicoverpa armigera has been used to study the expression of cytochrome P450 and cytochrome b5 mRNAs. Northern analysis showed that levels of the mRNAs for cytochrome P450s, CYP6B2, CYP6B6 and CYP6B7, and cytochrome b5 in control tissue were commensurate with those in the tissue of whole larvae. Substantial induction of cytochrome P450, CYP6B7 and cytochrome b5 mRNAs by alpha-pinene, and the pyrethroids, fenvalerate, cypermethrin and permethrin were observed in fat body culture. Neither mRNA was induced, either in midgut or integument organ cultures. In contrast, the relatively water-soluble compound phenobarbital, could induce CYP6B7 mRNA but not cytochrome b5 mRNA in fat body cultures. As for pyrethroids, phenobarbital had no effect on the other tissues in culture. These results confirm a previous conclusion that pyrethroids could induce CYP6B7 mRNA, which was based upon a very slight induction observed in living insects. Because many cytochrome P450 substrates can act as their inducers, these results support a previous conclusion that CYP6B7 could be the enzyme that is involved in pyrethroid resistance in H. armigera.
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