GENTECH archive


Re: TR: Bt toxins

	Is anyone familiar with the most recent studies of aflatoxin's
carcinogenity in animals fed Aspergillus-contaminated peanut meal?  The
FDA relaxed the rule for domestic use in feed from <20ppb to <300 ppb some
years back after it appeared that its dangers had been exaggerated; has
anyone established a threshold of certainty for carcinogenesis?  The meal
I am concerned with may be up to 2500ppb.

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On Fri, 27 Nov 1998, Edo Lin wrote:

> Clive Newel wrote:
> I read this claim recently:
> > Toxins used in transgenic food crops are plant-produced Bt
> > toxins called cry" toxins and they can be modified for specific
> > results, such as to kill only unwanted insects. Also, these Bt
> > toxins are only present in plant foliage, not the grain
> I have heard the opposite claimed, that the toxins are present in all parts 
> of the plant. I have heard that "every mouthful of Bt potato contains a 
> dose of Bt pesticide"
> Where does the truth lie?
> Clive Elwell
> The toxins you refer to are proteins expressed by specific genes from the 
> common soil bacteria Bacillus thuringiensis.
> With modern biotechnology, these genes can be introduced into plants, 
> letting the plant express these proteins.
> There are hybdreds of different Bt genes identified, each coding for 
> different proteins. Each toxin has a very specific mode of action, most 
> work on the destructionof the insect (mid) gut, thus preventing the insect 
> from further feeding and damage to the plant. The toxins identified have 
> been classified with the pre-fix Cry. For exmple, the most used Bt gene at 
> the moment in maize is Cry1A(b). The toxins are also very specific 
> regarding the insect on which it is active.
> Cry1A(b) is toxic to certain lepidopterous species such as European corn 
> borer but is not toxic to ladybeetles or bees or other insect genera.
> Other known Bt expressed proteins are active against for instance 
> mosquitoes, beetles, ants , nematodes etc etc.
> Where and how the plant expresses the protein is regulated by the promotor 
> used in the gene construct inserted into the plants. By choosing the right 
> promotor, protein expression could for instance be limited to the  green 
> leaves or to the roots or, if desirable, be expressed in all plant tissues 
> at the same time. The first approved Bt maize for instance has protein 
> expression limited to the green leaves and pollen and is not present in the 
> grains.
> If the protein is expressed in all plant parts, it would be true to say 
> that you get a mouthful of Bt protein. As the protein is only toxic to 
> certain target insect pests and not humans, it is not correct to say that 
> you ingest toxins when eating Bt plants.
> Edo Lin
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