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ISIS Report April 8, 2001
GM Crops May All Be Unstable
ISIS has drawn attention to the instability of GMOs and GM constructs
all along. Prof. Joe Cummins offers this
latest verdict, all GM crops may be unstable.
It is repeatedly claimed that genetically modified (GM) crops are
altered with single genes that are stable and equivalent to the genes that have
been selected and bred into the crops. In every case the GM crops originated
from cell cultures that have been know to be vexed with a phenomenon called
somaclonal variation. Somaclonal variation has been encountered in genetic
transformation using both biolistic and Agrobacterium transformation
followed by cell culture to isolate desirable agricultural characteristics. The
phenomenon is that cell cultures leading to isolate individual clones and
plants are plagued by genetic instability caused both by gene mutation and
chromosome rearrangement. In extreme responses plants may be infertile and the
extensive mutation leads to undesirable toxic natural products being produced.
Furthermore, the transgenes introduced into the modified crop are recognized as
invaders by the crop being transformed and the invading genes are silenced by
mechanisms including DNA methylation or gene inactivation at transcription.
The evidence that the genetic instability resulting in somaclonal
variation is caused by activation of inactive virus like genetic elements
called transposons is currently very compelling (see Courtial et al 2001).
Activated transposons create both gene mutation and
chromosome
rearrangement. On top of the somaclonal impact the inserted transgenes are
frequently silenced (see Demeke et al 1999). Even the most widely distributed
commercial GM crops such as Roundup Ready soy were found to contain unexplained
DNA sequences in the gene for herbicide resistance after ten years of
cultivation (Palevitz 2000). The
promised peer review publication on the
aberrant DNA sequences was not located and similar problems with similar
transformations in corn, cotton or canola have not yet been studied. Certainly,
government regulators and their academic satellites seem passive and submissive
in dealing with important findings reflecting on the safety of GM crops.
Even though the stability and long term stability of transgenic crops is
of paramount importance there have been few published studies on the genetic
stability and response to varying environments of transgenic crops. A study of
transgenic barley showed that GM barley was inferior to conventional barley in
a number of genetic backgrounds and
environmental conditions (Horvath et
al 2001). Such problems may reflect somaclonal variation or unexpected gene
silencing, or they may reflect other unpredicted aspects of genetic
modification. In conclusion, there should be a moratorium on the use and
distribution of GM crops until the consequences of genetic instability are
fully
explored. Government regulators should not be allowed to ignore the
consequences of allowing sudden revelations about DNA sequences that crop up
unexpectedly in commercial crops sold as unlabelled food to unsuspecting
people.
References
- Courtail,B,Fenebach,F,Ebehard,S,Rhomer,L,Chiapello,H,Carilleri,C and
Lucas,H "Tnt 1 transposition events are induced by in vitro transformation of
Aradopsis thaliana, and transposed copies integrated into genes" 2001 Mol Gen
Genomics 265,32-42
- Demeke,T,Hucl,P,Baga,M,Caswell,K,Leung,N and Chibar,R "Transgene
inheritance and silencing in hexaploid spring wheat" 1999 Theor Appl Genet
99,947-53
- Horvath,H,Jensen,L,Wong,O,kohl,E,Ullrich,S,Cochran,J,Kannangara,C,
and von Wettstein,D "Stability of transgene expression , field performance and
recombination breeding of transformed barley lines"2001 Theor Appl Genet
2001,1-11
- Palevitz,B "DNA surprise: Monsanto discovers extra sequence in its
Roundup Ready soybeans" 2000 The scientist 14,20 (july 24)
For further details please constact Prof. Joe Cummins at:
jcummins@uwo.ca
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