Bt maize had changed lipid composition in stems; also, lipid
composition in soil was altered, and soil respiration was reduced.
Maize (Zea mays).
crylAb gene from Bacillus thuringiensis (Bt). This gene
gives transgenic Bt maize (also called Bt corn) the ability
to produce insecticidal delta-endotoxin that can kill the larvae of the
European corn borer and other insect pests feeding on the corn. The gene
was fused to the cauliflower mosaic virus (CaMV-35S) promoter so that
the Bt gene would be expressed in all parts of the plant.
Goal of This Study:
Examine whether Bt maize differs from its nontransgenic
conventional counterpart in respect to (1) extractable lipids in the
plant stems, (2) extractable lipids in the soil in which the plants
had been cultivated, and (3) soil respiration in soils in which the
plants had been cultivated and which also contained plant residues. Soil
respiration is an indicator of the intensity of the breakdown of organic
matter, mainly through microbial soil organisms. The researchers used
a commercial variety of Bt maize (Pioneer 38W36) and compared it
to its non-genetically modified conventional counterpart (Pioneer 3893).
Results of This Study:
The researchers found:
The authors conclude: "The concerns raised by our data are serious enough
to emphasize the need to further research the impact of Bt maize
on short- and long-term soil quality" (p. 218).
Significant differences in the concentrations of different
extractable lipids in the stems (shoots) of Bt and conventional
maize. "Bt shoots were significantly lower in alkenes but richer
in n-alkanes, n-fatty and unsaturated fatty acids than non-Bt
shoots" (p. 217). Some of the specific differences included:
Concentrations of total alkenes (unsaturated hydrocarbons) in conventional
maize stems was 47.9% higher than in Bt maize stems.
One alkene type was missing altogether in Bt stems. A different
alkene made up half of the total alkene content in Bt maize and
only 13% in conventional maize.
In Bt maize there was also a shift in concentrations of the
different n-alkanes (saturated hydrocarbons); for example, one type made
up 25% of the n-alkanes in Bt maize stems while the same n-alkane
made up only 3% of total n-alkanes in conventional maize stems.
Significant differences in the concentrations of different extractable
lipids in soils in which Bt maize and conventional maize had
been grown. "Bt soils were lower in alkenes and unsaturated fatty
acids but richer in n-alkanes and n-fatty acids than non-Bt soils"
(p. 217). Some of the specific differences included:
Total alkane concentrations were 21.3% higher in soils in which
conventional maize grew.
"One striking feature was the dominance of unsaturated fatty acids
in non-Bt soils.... [while in] Bt soils n-fatty acid
concentrations were twice as high as those in non-Bt soils"
(p.216 and p. 217).
Significant differences in soil respiration. Respiration decreased
by 30.5% under Bt crops. This "soil respiration study strongly
suggests that the chemical nature of the Bt maize shoots and their
biological reactivity, as indicated by the extractable lipids, are changed
following gene modifications.... Cultivation of Bt maize appears
to significantly increase the saturated to unsaturated lipid relation in
soils and so affect soil microbial activity. Loss of unsaturated lipids
from Bt soils may lower the chemical reactivities of these soils"
Dinel, H., M. Schnitzer, M. Saharinen, F. Meloche et al. (2003).
"Extractable Soil Lipids and Microbial Activity as Affected by Bt
and Non Bt Maize Grown on a Silty Clay Loam Soil," Journal of
Environmental Science and Health Part B vol. B38 pp. 211-19.
Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food
Canada; University of Potenza, Italy.
Bt maize has been commercially grown since the late 1990s.
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