Mechanism of cellular absorption of imidazolinones in soybean (Glycine max) leaf discs

The mechanism of uptake of imazapyr, imazethapyr, and imazaquin into soybean leaf discs was determined. Uptake into the leaf discs was linear with respect to external concentration from 10−8 to 10−3 M. Metabolic inhibitors and uncouplers (DNP, FCCP, CCCP, NaN3, NaCN, DCMU) decreased uptake 58 to 85 %. Uptake was also sensitive to temperature, with maximum uptake occurring at 23°C. The Q10 for uptake between 13 and 23°C was 1‐7. The uptake of all 3 imidazolinones was sensitive to the pH of the uptake solution. Maximum uptake occurred at pH 4. However, there were differences in the rate of uptake among the three herbicides. Imazaquin was absorbed the most rapidly followed by imazethapyr and then imazapyr. These differences in uptake reflected the differences in the lipophilicity of the chemicals at pH 4 and 7. The apparent Kow of imazaquin, imazethapyr and imazapyr at pH 4 was 7‐7, 1‐4, and 0‐1, respectively, and at pH 7 was 0‐04, 0‐02, and 0‐004, respectively. Based on these results the mechanism of uptake is probably best explained by ion trapping.