title: Glyphosate-resistant horseweed made sensitive to glyphosate: low-temperature suppression of glyphosate vacuolar sequestration revealed by 31P NMR.
abstract: BACKGROUND
  Horseweed has been the most invasive glyphosate-resistant (GR) weed, spreading to 16 states in the United States and found on five continents. The authors have previously reported that GR horseweed employs rapid vacuolar sequestration of glyphosate, presumably via a tonoplast transporter, substantively to reduce cytosolic glyphosate concentrations.1 It was hypothesized that glyphosate sequestration was the herbicide resistance mechanism. If resistance is indeed endowed by glyphosate sequestration, suppression of sequestration offers the potential for controlling GR horseweed at normal herbicide field-use rates.
  
  
  RESULTS
  Low-temperature (31) P NMR experiments performed in vivo with GR cold-acclimated horseweed showed markedly suppressed vacuolar accumulation of glyphosate even 3 days after glyphosate treatment. [In stark contrast, 85% of the visible glyphosate was sequestered 24 h after spraying warm-acclimated GR horseweed.] Cold-acclimated GR horseweed treated at normal use rates and maintained at low temperature succumbed to the lethal effects of glyphosate over a 40 day period. Treatment of GR horseweed in the field when temperatures were cooler showed the predicted positive herbicidal response.
  
  
  CONCLUSIONS
  Low temperature markedly diminishes vacuolar sequestration of glyphosate in the GR horseweed biotype, yielding a herbicide response equivalent to that of the sensitive biotype. This supports the recent hypothesis1 that glyphosate sequestration is the resistance mechanism employed by GR horseweed.
authors.affiliation: Department of Chemistry, Washington University, St Louis, MO, USA.
authors.forename: Xia
authors.initials: X
authors.lastname: Ge
authors.forename: Dana André
authors.initials: DA
authors.lastname: d'Avignon
authors.forename: Joseph J H
authors.initials: JJ
authors.lastname: Ackerman
authors.forename: Bill
authors.initials: B
authors.lastname: Duncan
authors.forename: Marvin B
authors.initials: MB
authors.lastname: Spaur
authors.forename: Robert Douglas
authors.initials: RD
authors.lastname: Sammons
mesh_terms: D003080:Cold Temperature; D035401:Conyza / Q000737:chemistry; D005998:Glycine / Q000031:analogs & derivatives*; D053209:Herbicide Resistance; D006540:Herbicides; D009682:Magnetic Resonance Spectroscopy; D010759:Phosphorus Isotopes / Q000032:analysis; D014617:Vacuoles / Q000737:chemistry*; D000097797:Glyphosate
chemical_list: D005998:Glycine; D006540:Herbicides; D010759:Phosphorus Isotopes; D000097797:Glyphosate