Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 3, 2010
Publication Date: January 7, 2011
Citation: Cook, D., Gardner, D.R., Grum, D.S., Pfister, J.A., Ralphs, M.H., Welch, K.D., Green, B.T. 2011. Swainsonine and endophyte relationships in Astragalus mollissimus and Astragalus lentiginosus. Journal of Agricultural and Food Chemistry. 59(4):1281-7. Interpretive Summary: A fungal endophyte (Undifilum oxytropis) is responsible for the synthesis of swainsonine in Oxytropis and Astragalus species, commonly known as locoweeds. The distribution of swainsonine concentrations and endophyte amounts in different plant parts of Astragalus lentiginosus and Astragalus mollissimus was investigated. Two chemotypes of both species were identified: one that accumulated high concentrations of swainsonine and another where swainsonine was not detected or concentrations that were near the detection threshold. The plants with high swainsonine concentrations had quantitatively higher amounts of endophyte. Alternatively, plants where swainsonine was not detected or concentrations that were near the detection threshold had quantitatively lower endophyte amounts. Furthermore, swainsonine and endophyte amounts were shown to not be uniformly distributed from the same plant.
Technical Abstract: Locoweeds are defined as Astragalus and Oxytropis species that contain the toxic alkaloid swainsonine. Swainsonine was detected in all parts of Astragalus lentiginosus and Astragalus mollissimus with greater concentrations found in the above ground parts. Undifilum oxytropis, a fungal endophyte responsible for the synthesis of swainsonine, was detected in all plant parts of Astragalus lentiginosus and Astragalus mollissimus. At times the amount of endophyte within a plant part does not correspond to the concentration of swainsonine in the same part. Plants of Astragalus mollissimus and Astragalus lentiginosus can be divided into two chemotypes: those that contain swainsonine (> 0.1%; chemotype 1) and those that contain little or no detectable swainsonine (< 0.01%; chemotype 2). Chemotype 1 plants in both species had quantitatively higher amounts of endophyte compared to chemotype 2 plants. Swainsonine and endophyte amounts were not uniformly distributed within stalks. For that reason, repeated sampling of stalks from the same plant during one growing season may provide misleading results. Endophyte haplotypes of Undifilum oxytropis exist within populations of Astragalus mollissimus, Astragalus lentiginosus, and O. sericea and do not correlate with chemotype. These findings suggest several possible reasons for differential concentrations of swainsonine that will be tested in future work.