Sethoxydim-Uptake by Leaf Slices of Sethoxydim Resistant and Sensitive Grasses

Leaf slices of the sethoxydim sensitive grasses Poa pratensis and Festuca ovina and the sethoxy­ dim resistant grasses Poa annua and Festuca rubra take up the herbicide at similar rates. Uptake is almost linear with concentration up to 2 m M , independent of light and little affected by tempera­ ture between 0 and 25 °C. Uptake is highly pH sensitive. At pH 7.0 rates o f uptake are only about 20% of the rates observed at pH 3.5. Time course of uptake suggests a rapid equilibration of the compartments taking up the herbicide within 2 h. It is suggested that sethoxydim uptake by the grass-leaf tissue is a nonspecific process involving passive lipid diffusion and lipid equilibration of the non-dissociated weak acid sethoxydim (pKa = 4 .6).