NICOSULFURON, PRIMISULFURON, AND BENTAZON HYDROXYLATION BY CORN (ZEA-MAYS), WOOLLY CUPGRASS (ERIOCHLOA-VILLOSA), AND SHATTERCANE (SORGHUM-BICOLOR) CYTOCHROME-P-450

Microsomes (100,000 g pellet containing mixed membrane fractions but p rimarily endoplasmic reticulum) were isolated from shoots of corn, sha ttercane, and woolly cupgrass grown from naphthalic anhydride treated or untreated seed to determine if metabolism of bentazon, nicosulfuron , and primisulfuron could be demonstrated in the preparations. Corn is tolerant of all three herbicides, shattercane is tolerant of bentazon , and woolly cupgrass is tolerant of bentazon and primisulfuron. Napht halic anhydride treatment was required for detectable bentazon, nicosu lfuron, and primisulfuron hydroxylation in corn microsomes and for ben tazon hydroxylation in woolly cupgrass microsomes. Bentazon hydroxylat ion was low, but detectable, in microsomes from shattercane shoots wit hout naphthalic anhydride treatment. Naphthalic anhydride-treated corn microsomes hydroxylated 292, 120, and 52 pmol mg(-1) protein min(-1) of bentazon, nicosulfuron, and primisulfuron, respectively. Primisulfu ron (19 pmol mg(-1) protein min(-1)), but not nicosulfuron, was hydrox ylated in woolly cupgrass microsomes. Neither nicosulfuron nor primisu lfuron was hydroxylated in shattercane microsomes. Bentazon and primis ulfuron inhibited nicosulfuron hydroxylation in corn microsomes. Benta zon, but not nicosulfuron, also inhibited primisulfuron hydroxylation in the corn microsomes. This indicates that the three herbicides can i nteract at the same cytochrome P-450(s) in corn. Primisulfuron hydroxy lation was not inhibited by either bentazon or nicosulfuron in woolly cupgrass microsomes. This suggests that the cytochrome P-450(s) for pr imisulfuron hydroxylation are different between corn and woolly cupgra ss. Also, bentazon hydroxylation in corn and shattercane microsomes wa s inhibited by the cytochrome P-450 inhibitor tetcyclasis, while that in woolly cupgrass was not. Again, this suggests a difference in the c ytochrome P-450(s) responsible for bentazon metabolism among the speci es. Although absolute conclusions comparing in vitro microsomal activi ties to whole plant herbicide tolerance cannot be made because it is u nknown whether the same cytochrome P-450(s) are studied in microsomes from naphthalic anhydride-treated tissue as are responsible for in viv o herbicide metabolism, there was a broad correlation between metaboli sm of a particular herbicide in microsomes of a species and the specie s' tolerance of that herbicide.