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Title: Metabolic profiling and enzyme analyses indicate a potential role of antioxidant systems in complementing glyphosate resistance in an Amaranthus palmeri biotype

Author
item MAROLI, AMITH - Clemson University
item Nandula, Vijay
item Dayan, Franck
item Duke, Stephen
item GERARD, PATRICK - Clemson University
item THARAYIL, NISHANTH - Clemson University

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2015
Publication Date: 9/2/2015
Publication URL: http://handle.nal.usda.gov/10113/62230
Citation: Maroli, A.S., Nandula, V.K., Dayan, F.E., Duke, S.O., Gerard, P., Tharayil, N. 2015. Metabolic profiling and enzyme analyses indicate a potential role of antioxidant systems in complementing glyphosate resistance in an Amaranthus palmeri biotype. Journal of Agricultural and Food Chemistry. 63:9199-9209.

Interpretive Summary: Glyphosate-resistant (GR) Palmer amaranth is the biggest weed problem in the Southeastern US. It is primarily resistant due to gene amplification increasing the number of target enzyme molecules needed to be inhibited by the herbicide to kill the plant. This metabolomic and biochemical study of GR Palmer amaranth and a non-GR biotype of the weed found that the resistant form of this weed has higher levels of some antioxidant phenolic compounds and rapidly quenches oxidative stress caused by glyphosate. These findings suggest that these properties of the GR form of the weed may complement gene amplification-mediated glyphosate resistance.

Technical Abstract: Targeted metabolomic profiling and biochemical assays were employed to identify metabolite-level perturbations induced by glyphosate in susceptible (S) and resistant (R) biotypes of Amaranthus palmeri. Plants were treated with 0.4 kg ae ha-1 glyphosate and tissues were harvested at 8 and 72 hours after treatment (HAT). At 8 HAT, irrespective of the biotypes, hierarchical cluster analysis of 60 identified metabolites grouped herbicide-treated and the control to distinct clusters, while at 72 HAT only the glyphosate treated S-biotype was different, indicating that the R biotype recovered from an initial toxic effect. Shikimic acid accumulated in both R- and S-biotypes in response to glyphosate application within 8 HAT, which was accompanied by an increase in organic acids and aromatic amino acids in the R-biotype, while the S-biotype had higher amounts of sugars and branched-chain amino acids. The R-biotype had lower reactive oxygen species (ROS) effects and higher ROS scavenging activity than the S-biotype. Higher levels of secondary compounds of the shikimate pathway (ferulic acid, caffeic acid, and 4-O-feruloylquinic acid) were found in the untreated R than S biotype. Metabolic profiling in conjunction with biochemical assays indicate that glyphosate-induced metabolic perturbations in both R and S biotypes of A. palmeri and that ROS might have scavenging helped to overcome an initial phytotoxic effect in the R biotype.