Translocation and Metabolism of MAA-14C in Johnsongrass and Cotton

Abstract

Radioautographs showed that root uptake of14C-methanearsonic acid (MAA-14C) by johnsongrass (Sorghum halepense(L.) Pers.) from nutrient solution was rapid and translocation into all portions of the plant occurred within 4 hr after treatment. Basipetal and acropetal translocation of foliar and stem-applied MAA-14C occurred in both johnsongrass and cotton (Gossypium hirsutumL., var. Rex smooth leaf), indicating that movement of the herbicide probably occurs in both phloem and xylem tissue. However, acropetal movement of MAA in both plants occurred at a higher rate than basipetal movement, and basipetal movement in cotton was not as rapid as in johnsongrass. Methanol extracts of MAA-14C johnsongrass were chromatographed. Radioactive spots with Rfvalues different from the MAA-14C standard were observed. Use of location reagents on the chromatographs suggested that MAA-14C may complex with either a sugar or organic acid or both. Amino acid fractions were prepared from methanol extracts of both plants. An MAA metabolite, with a positive reaction to ninhydrin, was located on chromatographs spotted with the amino acid fraction from johnsongrass but was not present in the cotton fraction. A comparison of Rfvalues suggests that the metabolite may be a combination of the MAA molecule with histidine or one of its analogues. Spectrophotometric determination showed a build-up of amino acids in MAA-treated johnsongrass but not in cotton. The increased levels of amino acids in johnsongrass suggest that the MAA metabolite may be blocking a protein synthesis pathway, or some other unknown biosynthetic pathway.