Factors Affecting Miserotoxin Metabolism in Timber Milkvetch

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Abstract
Three poisonous varieties of timber milkvetch (Astragalus miser Dougl. ex Hook.) were grown under different temperature regimes in growth chambers. Miserotoxin, the poisonous chemical in timber milkvetch, was in greater concentration in plants grown at higher day temperatures (32 C) than at 24 C. In the field, nitrogen fertilizers did not affect miserotoxin synthesis in any variety, but significantly increased plant nitrogen in two varieties. Excluding light from Yellowstone milkvetch [var. hylophilus (Rydb.) Barneby] for 2 weeks significantly lowered miserotoxin concentration. Miserotoxin level in timber milkvetch was reduced when photosynthesis (a) was blocked by subjecting plants to prolonged darkness; (b) was disrupted by treating plants with 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] or silvex [2-(2,4,5-trichlorophenoxy)propionic acid]; (c) was reduced by lowered day temperature; (d) was terminated by senescence and bleaching.

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