Phytotoxicity and metabolism of ethofumesate in transgenic rice plants expressing the human CYP2B6 gene

Transgenic rice plants expressing human CYP1A1, CYP2B6, or CYP2C19 show strong cross-tolerance to various herbicides. However, these plants showed susceptibility to the herbicides ethofumesate and benfuresate. Both herbicides inhibited germination of transgenic rice plants at a concentration of 2.0 muM in the culture medium, whereas control Nipponbare plants showed normal growth in their presence. The CYP2B6 rice plants metabolized ethofumesate to produce the de-ethylated metabolite DHDBM (2,3-dihydro-2-hydroxy-3,3-dimethyl-5-benzofuranyI methanesulfonate), which was accumulated to levels up to 60 times higher than in control plants. Germination of both control and CYP2B6 rice plants was inhibited completely with 0.75 muM DHDBM in the culture medium. The phytotoxicity of DHDBM to rice plants was at least four times greater than that of ethofumesate. Because both ethofumesate and benfuresate are metabolized to give DHDBM or analogous metabolites, we consider that DHDBM was the major phytotoxic metabolite in these rice plants. (C) 2003 Elsevier Science (USA). All rights reserved.