Glyphosate-resistant soybeans exuded glyphosate, carbohydrates,
and amino acids into the soil and affected the microorganism soil
community.
Manipulated Organism:
Soybean (Glycine max).
Inserted Transgene and Target Effect:
CP4 EPSPS gene derived from the common soil bacterium
Agrobacterium sp., Strain CP4, to convey resistance to the
herbicide glyphosate (Roundup). The gene was fused to the cauliflower
mosaic virus (CaMV-35S) promoter so that it would be expressed in all
parts of the plant.
Goal of This Study:
Part of the context of this study was the observation that field-grown
glyphosate-resistant soybean roots were observed to be highly colonized
by the fungus Fusarium, a species which is the infectious agent in
soybean sudden death syndrome. The researchers investigated (1) whether
glyphosate is exuded into the soil by the roots of transgenic soybeans;
(2) whether glyphosate-resistant soybean roots release other substances
in changed concentrations; and (3) whether what glyphosate-resistant
soybean roots release has any effects on soil fungi and bacteria. The
study used a commercial variety of glyphosate-resistant soybean (Pioneer
94B01) and compared it to a conventional soybean variety, Williams 82,
which is susceptible to glyphosate.
Results of This Study:
researchers carried out laboratory investigations and found that:
-
Glyphosate-resistant soybeans treated with glyphosate exude glyphosate
via their roots into the soil environment while they grow.
-
Glyphosate-resistant soybeans, whether treated with glyphosate or
not, exuded via their roots higher amounts (approx. 30% higher) of
carbohydrates into the soil than unmanipulated controls (treated with
glyphosate and without).
-
Glyphosate-resistant soybeans treated with glyphosate exuded via their
roots significantly more amino acids into the soil than unmanipulated
control soybeans treated with glyphosate (40% higher concentration after
16 days);
-
Strains 301 and 304 of the soil fungus Fusarium grew more
profusely when they were grown in the material exuded from the roots
of glyphosate-treated soybeans and grew best in the exudates from the
glyphosate-resistant plants.
-
Fusarium strain 206 grew significantly better when grown in
the material exuded from the roots of glyphosate-resistant soybeans,
regardless of whether the plants had been treated with glyphosate or
not.
-
"Bacterial growth generally decreased in root exudates of
glyphosate-treated plants" (p. 1171).
Additional Comments:
Since the glyphosate-resistant soybeans differed from the unmanipulated
cultivar in the amounts of carbohydrates and amino acids released
into the soil, independent of treatment with glyphosate, the authors
remark: "Our observations suggest that some mechanism(s) affecting
carbohydrate and amino acid translocation and release through roots by GR
[glyphosate-resistant] soybean was affected during genetic modification
for glyphosate resistance" (p. 1171).
Moreover, the release of glyphosate, carbohydrates, and amino acids into
the soil via the roots of the transgenic soil has an effect on the growth
of select soil fungi and bacteria, and could, under field conditions,
contribute to significant shifts in the microorganism soil community.
Source:
Kremer, R. J., N. E. Means, and S. Kim (2005). "Glyphosate
Affects Soybean Root Exudation and Rhizosphere Micro-Organisms,"
Intern. J. Environ. Anal. Chem. vol. 85, pp. 1165-74.
Author Affiliations:
USDA, Agricultural Research Service, Cropping Systems & Water Quality
Research Unit, Columbia, Missouri; Department of Soil, Environmental &
Atmospheric Sciences, University of Missouri, Columbia, Missouri.
Funding:
USDA grant and grant from Ag Spectrum Company, Dewitt, Iowa (partial).
Product Status:
The variety of glyphosate-resistant soybeans used in the experiment is
one of many commercial varieties of glyphosate-resistant soybeans sold
in the U.S.
Copyright 2008 The Nature
Institute.
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