MODELING ROOT ABSORPTION AND TRANSLOCATION OF 5-SUBSTITUTED ANALOGS OF THE IMIDAZOLINONE HERBICIDE, IMAZAPYR

Quantitative structure-activity relationships (QSAR) were developed be tween the physicochemical parameters of the 5-substituent of a series of analogs of the imidazolinone herbicide, imazapyr, and root absorpti on, translocation, inhibition of acetohydroxyacid synthase (AHAS), and herbicidal activity of the analogs. An optimum substituent lipophilic ity (pi = 1.85-2.3) for root absorption was identified for com (Zea ma ys L.) and sunflower (Helianthus annuus L.). Translocation from roots to shoots was greatest for those analogs having either highly nonpolar or highly polar 5-substituents, indicating that both symplastic and a poplastic mechanisms may be functioning. In addition, translocation fr om roots was positively correlated with electron-withdrawing parameter s of the 5-substituent, and a possible mechanism governing this relati onship is discussed. Modeling in vitro AHAS inhibition was not success ful, but models were developed for herbicidal activity as measured in an Arabidopsis thaliana (L.) Heynh. bioassay. The whole-plant models d escribed an optimum substituent lipophilicity (pi = 0.71) which probab ly reflected the influence of this parameter on the component processe s of absorption and translocation. Whole-plant activity was also great er for analogs having electron-donating 5-substituents, this result su ggests that electron donation may be important for metabolism, or more likely, for AHAS inhibition.