>It may well be that the Bt gene is in every cell in the plant, but that is several biological processes short of the *toxin* being in every cell of the plant. Since the toxin is a protein, you've got to get through transcription and translation before it's even present. I don't know what expression system is controlling expression of that gene, so it may well be broadly expressed, or it may be a tissue specific expression.
It would not be very effective as an insecticide if it's not at least in the tissue of the plant that the larvae are eating. I usually see the larvae on the ears, which happens to be the part we eat. It's in the pollen, hence the research on it's effect on Monarchs.
> Then, even if the toxin is expressed in every cell of the plant, there are really good (scientifically based) reasons to think that it is not a problem for humans - short term or long term. For the toxin to be effective, it must first become soluble in the gut, which has been repeatedly demonstrated to require an alkaline gut pH (why it works on insects and not humans)
Like infants have...
> then it has to go through a pH driven conformational change (again requiring alkaline pH), then it has to interact with and be modified by host-specific proteases to convert the "raw" form to the active form, then it has to interact with host specific receptors to form complexes which are inserted into the gut wall causing the eventual physiological response. (
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1857359/)
This is in order to act in the same way it does on the insect larvae, but what is the effect long term of eating this protein, even if it is not doing direct damage? Allergic responses to our food? Other issues? I know it does not affect humans in the same way as insects, but we still don't know the long term effects of exposure to this toxin.
> Bt toxins are not even broad based in their effects on insects. Due to the host-specific nature of a couple of the steps, Bt toxins only affect certain classes of insects, depending on the Bt species from which the toxin was isolated.
Insects have very short lives. If the toxin is not directly effective in their digestive track, they don't have time to develop other reactions to it. We live long enough for that to happen.