Glyphosate-Resistant and Conventional Canola (Brassica napus L.) Responses to Glyphosate and Aminomethylphosphonic Acid (AMPA) Treatment.
Glyphosate-resistant (GR) canola contains two transgenes that impart resistance to the herbicide glyphosate: (1) the microbial glyphosate oxidase gene (gox) encoding the glyphosate oxidase enzyme (GOX) that metabolizes glyphosate to aminomethylphosphonic acid (AMPA) and (2) cp4 that encodes a GR form of the glyphosate target enzyme 5-enolpyruvylshikimic acid-3-phosphate synthase. The objectives of this research were to determine the phytotoxicity of AMPA to canola, the relative metabolism of glyphosate to AMPA in GR and conventional non-GR (NGR) canola, and AMPA pool sizes in glyphosate-treated GR canola. AMPA applied at 1.0 kg ha(-1) was not phytotoxic to GR or NGR. At this AMPA application rate, NGR canola accumulated a higher concentration of AMPA in its tissues than GR canola. At rates of 1 and 3.33 kg ae ha(-1) of glyphosate, GR canola growth was stimulated. This stimulatory effect is similar to that of much lower doses of glyphosate on NGR canola. Both shikimate and AMPA accumulated in tissues of these glyphosate-treated plants. In a separate experiment in which young GR and NGR canola plants were treated with non-phytotoxic levels of [(14)C]-glyphosate, very little glyphosate was metabolized in NGR plants, whereas most of the glyphosate was metabolized to AMPA in GR plants at 7 days after application. Untreated leaves of GR plants accumulated only metabolites (mostly AMPA) of glyphosate, indicating that GOX activity is very high in the youngest leaves. These data indicate that more glyphosate is transformed to AMPA rapidly in GR canola and that the accumulated AMPA is not toxic to the canola plant.
UNESP, Universidade Estadual Paulista "Júlio de Mesquita Filho", Campus de Registro/SP, Rua Nelson Brihi Badur 430, 11900-000 Registro, SP, Brazil.
Elza Alves
EA
Corrêa
Natural Products Utilization Research Unit, Agricultural Research Service, U.S. Department of Agriculture , P.O. Box 1848, University, Mississippi 38677, United States.
Franck E
FE
Dayan
Natural Products Utilization Research Unit, Agricultural Research Service, U.S. Department of Agriculture , P.O. Box 1848, University, Mississippi 38677, United States.
Daniel K
DK
Owens
Natural Products Utilization Research Unit, Agricultural Research Service, U.S. Department of Agriculture , P.O. Box 1848, University, Mississippi 38677, United States.
Agnes M
AM
Rimando
Natural Products Utilization Research Unit, Agricultural Research Service, U.S. Department of Agriculture , P.O. Box 1848, University, Mississippi 38677, United States.
Stephen O
SO
Duke
D029688:Brassica napus / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D053209:Herbicide Resistance; D006540:Herbicides / Q000494:pharmacology*; D007555:Isoxazoles; D063065:Organophosphonates / Q000494:pharmacology*; D030821:Plants, Genetically Modified / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D013777:Tetrazoles; D000097797:Glyphosate
D005998:Glycine; D006540:Herbicides; D007555:Isoxazoles; D063065:Organophosphonates; D013777:Tetrazoles; D000097797:Glyphosate; C418233:2-amino-3-(3-hydrox-5(2-methyl-2H-tetrazol-5-yl)isoxazol-4-yl)propionic acid
5-enolpyruvylshikimic acid-3-phosphate synthase; AMPA; Brassica napus; EPSPS; aminomethylphosphonic acid; canola; glyphosate; glyphosate oxidase