"I was initially very skeptical," says d'Avignon. "My feeling was that, because a living plant would present a very heterogeneous environment, we would not observe well-resolved phosphorus NMR signals from glyphosate, let alone pinpoint glyphosate's cellular handling.
"I was proved wrong," he says.
To attack the problem, d'Avignon assembled a team of chemists skilled in the field of NMR. Along with Sammons from Monsanto, he enlisted Xia Ge, PhD, a postdoctoral research associate, and Joseph Ackerman, PhD, the William Greenleaf Eliot Professor of Chemistry in Arts & Sciences.
D'Avignon's team focused its initial efforts on Conyza canadensis, also called mare's tail or horseweed, a fibrous biennial plant that can grow to be six feet tall with sparsely hairy stems and pale-green irregularly nicked leaves. (When it grows in a soybean field, it overtops the crop and can reduce yields by more than 80 percent.)
It is the most persistent of the glyphosate-resistant weeds and is already found in 19 states in the United States and separately on five continents.
The scientists sprayed horseweed plants with glyphosate and then examined living leaf tissue in the NMR instrument. They immediately saw that they could distinguish the glyphosate signal from those of other phosphorus-bearing plant metabolites, including the ubiquitous energy-storing molecule adenosine triphosphate (ATP).
Then they had a stroke of luck. During the time course of the data collection, a second glyphosate signal appeared at a slightly different resonance frequency. The first signal was coming from glyphosate in the cell cytoplasm and the
second from glyphosate in the plant vacuole, a large water-filled compartment found in all plant cells that can serve as a g
|Contact: Diana Lutz|
Washington University in St. Louis