Biochemical Effects of Sethoxydim in Excised Root Tips of Corn (Zea mays)

The effects of sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} on the metabolic activity of excised root tips of corn ( Zea mays , L. ‘Goldencrossbantam′) were studied under laboratory conditions. Uptake and incorporation of 14 C-labeled thymidine, uridine, leucine, glucose, and acetic acid into cell constituents, as well as respiration, increased continuously with time progressions during the incubation period. Sethoxydim did not affect either the uptake of any 14 C-precursor into or respiration of the root tip tissue. Although RNA and protein syntheses were not affected by the herbicide, DNA and cell wall syntheses were inhibited 120 min after treatment with sethoxydim. Incorporation of 14 C-acetic acid into lipid fraction was inhibited by sethoxydim in a time- and concentration-dependent fashion. This inhibition was observed at a shorter time after sethoxydim treatment than that of any other 14 C-precursor. The effect was not observed in the nonproliferative regions of corn roots, whereas cerulenin (a fatty acid synthase inhibitor) inhibited the incorporation of 14 C-acetic acid both in proliferative and nonproliferative regions. It is suggested that the inhibition of lipid synthesis by sethoxydim does not play a major role in the mode of action of this herbicide. The effects of sethoxydim, including those on lipid metabolism, are closely associated with proliferative conditions of susceptible graminaceous plants.