ISIS Report 25/11/04
Beware Monsanto’s "Vistive Soybeans"
Prof. Joe Cummins lifts the lid
on a new wave of genetically engineered products that claim to offer "healthier
foods" and "direct consumer benefits".
A fully referenced version
of this article is posted on ISIS members’ website.
Details here.
In September 2004, Monsanto announced a "Vistive soybean" with reduced
linolenic (low linolenic or LL) acid content that will be available for
planting in the 2005 season. Although promoted as "produced through
conventional breeding" because it includes natural genes reducing the oil
content of linolenic acid, Vistive also has transgenes conferring the Roundup
Ready trait.
Vistive soybean does not appear to have been approved under the usual
procedure for transgenic crops because the reduced linolenic acid content was
achieved using traditional selection and breeding. Instead, government
regulators assumed that the Roundup Ready trait acts independently of the LL
trait and for that reason the two kinds of traits could be joined by crossing
two strains.
Certainly, there is no precedent for reviewing and approving novel crops
produced by conventional breeding, but if the LL trait interacts with the
Roundup Ready (glyphosate tolerance) trait, Vistive soybeans should be
re-evaluated as an alteration to the original Roundup Ready trait. There is a
clear indication that the use of glyphosate on the soybean crop will result in
an impact on fatty acid metabolism through the breakdown products of the
herbicide (see later).
Vistive soybeans with the Roundup Ready trait are claimed to contain
less than 3% linolenic oil, in contrast to the 8% linolenic content for
conventional soy oil. Low linolenic oil is more stable, with a better flavour
and requires less hydrogenation. Trans fatty acids are produced in the
hydrogenation process; and trans fatty acids are linked to heart disease
because they lower HDL (good) cholesterol while raising LDL (bad) cholesterol.
Ironically, trans-fats labelling is to begin in 2006 in the United States, even
though industry and regulators in the United States resist labelling of
products containing transgenes.
In plants, fatty acids are produced in the chloroplasts. Two molecules
are crucial for fatty acid synthesis: acetyl-CoA and malonly-CoA (acetyl-CoA
with an added carbon dioxide molecule). The number of carbon atoms in the long
fatty acid chain is always even, and the carbon molecules are added two at a
time. The newly synthesized fatty acids may be altered in mitochondria, or the
endoplasmic reticulum, or stored in membrane bound lipid vesicles.
Catabolism of the fats is undertaken in organelles called glyoxysomes
where the fatty acids are degraded two carbon atoms at a time, by a process
called beta-oxidation. Fatty acids are modified in organelles and the
endoplasmic reticulum by the lipoxygenase pathway to produce plant defence and
signalling compounds such as jasmonates. Glyoxysomes carry out the glyoxylate
cycle - a modification of the tricarboxylic acid cycle found in plants and
microbes - as well as beta-oxidation. Fatty acid metabolism is crucial to
energy transformation in plants, but also contributes to cell structure and to
signalling and defence.
The transgenic parent of Vistive soybean is the soybean line GTS40-3-2
(event MON-04032-6), tolerant to glyphosate. The strain was released
commercially in the United States in 1994, then Canada (1995), Japan (1996),
Argentina (1996), Uruguay (1997), Mexico (1998), Brazil (1998) and South Africa
(2001). The transgenic construct includes a synthetic approximation of the
EPSPS gene from Agrobacterium for tolerance to glyphosate, adjusted for
the codon preference of the crop. The EPSPS gene was driven by the enhanced 35s
cauliflower mosaic virus promoter, and the sequence included a chloroplast
transit protein from petunia and a nopaline synthesis terminator from
Agrobacterium .
Six years after Roundup Ready soy was released to the environment,
Monsanto acknowledged that an "inactive" 75 base pair fragment and a 250 base
pair fragment of the EPSPS gene were inserted outside the open reading frame of
the EPSPS protein (those inserts were over 20% the size of the EPSPS gene). The
origin of the gene fragments and their possible activity was curtly dismissed
without fuller explanation. The evident instability of these and other crop
transgenes has been discussed by Mae-Wan Ho, and raises many biosafety
concerns.
Possible interactions between the LL and Roundup Ready genes of Vistive
soy cannot be dismissed, as the crop will certainly be sprayed with glyphosate.
The herbicide will accumulate to levels toxic to animals and humans if it is
not broken down in the plant cell. In plants, glyphosate is normally broken
down by glyphosate oxidase (GOX) enzyme (presumably an enzyme present to digest
natural products). GOX enzyme accelerates the breakdown of the herbicide
glyphosate into two compounds, aminomethylphosphonic acid (AMPA) and
glyoxylate. Glyoxylate is commonly found in plant cells and is further broken
down by the glyoxylic pathway for lipid metabolism. The increased concentration
of glyoxylate due to glyphosate breakdown would certainly disturb the
metabolism of fatty acids.
Glyphosate exposure of herbicide tolerant groundnut was observed to
increase glyoxylase enzyme. Presently, it is not possible to predict the nature
and extent of disturbance of fatty acid metabolism, nor the impact on LL
function. The point is that there is a clear link between Roundup Ready and LL
traits, which should be explored fully before the Vistive crop reaches general
distribution. Every transgenic crop should be reassessed after it has been
crossed with a variety derived from conventional selection, especially one that
has a clear metabolic association with the transgene, before any release of the
crop. There should be a rule to ensure that careful reassessment is done.
The burden of proving that releases such as Vistive are safe rests with
the proponent. Experiments must be done to ensure that the Roundup Ready genes
and the LL genes are independent of each other, and that any interactions are
fully risk assessed. In addition, Roundup Ready soybean itself should be
reassessed in light of new scientific evidence raising questions about
transgenic instability.
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