Metabolism of the herbicide isoproturon in wheat and soybean cell suspension cultures

The plant metabolism of the phenylurea herbicide isoproturon (IPU) was stud ied in aseptic cell suspension cultures of soybean and wheat. After incubat ion with the C-14-labeled herbicide (1 ppm) over 48 h, total metabolic rate s were 45-54%. The predominant metabolites in soybean were identified as mo nodesmethyl-IPU, 2-hydroxy-IPU, and 2-hydroxy-monodesmethyl-IPU. The major metabolic pathway identified for wheat was the conversion of IPU to 2-hydro xy-IPU as the primary metabolite and then to 2-hydroxy-monodesmethyl-IPU. 2 -Hydroxy-IPU and an olefinic metabolite (isopropenyl-IPU) are described her e for the first time. Metabolite identification was based on high-performan ce liquid chromatography retention times as well as time-of-flight/secondar y-ion mass spectrometry and H-1 nuclear magnetic resonance spectroscopy. Wh eat microsomes catalyzed the NADPH-dependent conversion of isoproturon to m onodesmethyl and 2-hydroxymonodesmethyl metabolites. 2-Hydroxy-IPU was only a minor enzymatic product so there was a remarkable difference between the primary cellular and enzymatic metabolites. C-14 Incorporation into the wh eat-insoluble residue fraction increased from 3% (48 h) to 14% (7 days). A sequential solubilization procedure indicated that binding occurred mainly to the operationally defined hemicellulose (65%) and lignin (10%) fractions . Simulated stomach conditions (pH 1, 37 degrees C, 24 h) released only abo ut 5% of total bound radioactivity. The similarity of IPU metabolism in mic robial, plant, and animal systems is discussed, with 2-hydroxymonodesmethyl -IPU being a common metabolite. (C) 1999 Academic Press.