2,4-dichlorophenoxyacetic acid metabolism in transgenic tolerant cotton (Gossypium hirsutum)

The metabolic fate of 2,4-dichlorophenoxyacetic acid (2,4-D) was studied in leaves, of transgenic 2,4-D-tolerant cotton (Gossypium hirsutum), which is obtained by transfer of the tfdA gene from the bacterium Alcaligenes eutro phus. The tdfA gene codes for a dioxygenase catalyzing the degradation of 2 ,4-D to 2,4-dichlorophenol (2,4-DCP). [phenyl-C-14]-2,4-D was administered by petiolar absorption followed by an 18 h water chase or converted to the isopropyl ester and sprayed onto the leaf surface; the leaves were harveste d 48 h later. The herbicide was degraded to 2,4-DCP by the bacterial enzyme expressed in the plants. 2,4-DCP was rapidly converted to more polar metab olites and was never found in detectable amounts. Metabolite structures wer e deduced from enzymatic hydrolysis studies and mass spectrometric analyses . The first metabolite was the glucoside conjugate of 2,4-DCP (2,4-DCP-beta -O-glucoside). The major terminal metabolites were two more complex glucos ides: 2,4-DCP-(6-O-malonyl)glucoside and 2,4-DCP-(6-O-sulfate)glucoside.