THE METABOLITES OF THE HERBICIDE L-PHOSPHINOTHRICIN (GLUFOSINATE) - IDENTIFICATION, STABILITY, AND MOBILITY IN TRANSGENIC, HERBICIDE-RESISTANT, AND UNTRANSFORMED PLANTS

The metabolism of the herbicide L-phosphinothricin (L-Pt) was analyzed in tobacco (Nicotiana tabacum), alfalfa (Medicago sativa), and carrot (Daucus carota). In transgenic, Pt-resistant plants expressing the Pt -N-acetyltransferase gene (pat), L-Pt was acetylated, resulting in two forms of N-acetyl-Pt (ac-Pt). In transgenic plants expressing only lo w pat-encoded acetylating activity as well as in genetically unmodifie d plants, three metabolic compounds 4-methylphosphinico-2-oxo-butanoic acid, 3-methylphosphinico-propanoic acid (MPP), and 4-methylphosphini co-2-hydroxy-butanoic acid (MHB) were identified. Hence, the transgene -encoded acetylation of L-Pt competes with a plant-specific degradatio n. The compounds MPP, MHB, and ac-Pt were found to be the final, stabl e products of the plant's metabolic pathways. The mobility of these st able compounds in the plant was investigated: L-Pt as well as the deri ved metabolites were found to be preferentially transported to the upp er regions of the plant.