Glyphosate-resistant soybeans have altered root nodules when
sprayed with glyphosate.
Manipulated Organism:
Soybean (Glycine max).
Inserted Transgenes:
CP4 EPSPS gene cloned from Agrobacterium, which produces
an herbicide-resistant version of the enzyme targeted by the herbicide
glyphosate (Roundup).
Goal of This Study:
Although glyphosate-resistant (GR) soybeans have a resistant form of
the EPSPS enzyme, the symbiotic bacteria Bradyrhizobium japonicum
that live in the soybean root nodules and fix nitrogen do not. The goal
of this study was to determine whether glyphosate interferes with this
symbiotic relationship.
Results of This Study:
-
In one greenhouse experiment, GR soybean root nodules increased in number
but decreased in weight when plants were sprayed with glyphosate.
-
In a different experiment, root biomass and total nitrogen content
decreased, in some cases by as much as 50%, when GR soybeans were sprayed
with glyphosate.
-
In growth chamber experiments under water stress, root nodule activity
(as measured by acetylene reduction) was lower when GR soybeans were
sprayed with glyphosate. According to the authors, this enhanced
sensitivity to water stress did not appear to be related to differences
in transpiration.
Source:
King, C. A., L. C. Purcell, and E. D. Vories (2001). "Plant growth and
Nitrogenase Activity of Glyphosate-tolerant Soybean in Response to
Foliar Glyphosate Applications," Agronomy Journal vol. 93,
pp. 179-86.
Author Affiliations:
University of Arkansas.
Funding:
Not mentioned.
Product Status:
Genetically modified, glyphosate-resistant soybeans have been grown
commercially in the U.S. since 1996 and currently constitute 90% of the
U.S. soybean crop.
Copyright 2009 The Nature
Institute.
|
|
