Comparative metabolism of atrazine and EPTC in proso millet ( Panicum miliaceum L.) and corn

Abstract

The purpose of this study was to examine the differential activities of proso millet ( Panicum miliaceum L.) and corn ( Zea mays L.) with respect to atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)- S-triazine] and EPTC ( S-ethyldipropyl thiocarbamate) metabolism. GSH- S-transferase was isolated from proso millet shoots and roots. When assayed spectrophotometrically using CDNB (1-chloro 2,4-dinitrobenzene) as a substrate, the shoot enzyme had only 10% of the activity of corn shoot enzyme while the root enzyme had 33% the activity of corn root enzyme. However, when proso millet shoot GSH- S-transferase was assayed in vitro using 14C-ring-labeled atrazine, it degraded the atrazine to water-soluble products at the same rate as the corn shoot enzyme. Incubation of excised proso millet and corn roots with [ 14C]EPTC indicated that uptake of EPTC was similar in both plants. However, proso millet metabolized the EPTC to water-soluble products at only half the rate of corn. Glutathione levels of proso millet roots were 35.9 μg GSH/g fresh wt, compared with 65.4 μg GSH/g fresh wt for corn. However, a 2.5-day pretreatment with R-25788 (N,N-diallyl-2-2-dichloroacetamide) elevated proso millet GSH levels to 62.7 μg GSH/g fresh wt. R-25788 did not elevate the activity of proso millet GSH- S-transferase, in contrast to its effects on corn. We conclude that differences in response to atrazine and EPTC in proso millet and corn are a result of their differential metabolism.