Uptake, translocation, and metabolism of MG-191 safener in corn (Zea mays L.)

The time-dependent uptake, translocation, and metabolism of [14C]MG-191 safener and the influence of EPTC on these processes were studied using 5-d-old corn seedlings grown in nutrient solution. Plants absorbed relatively low levels of root-applied radiolabel at both 10 KuM and 50 ,uM [14C]MG-191 rates durimg 6 d of exposure. Amounts of absorbed radioactivity increased with time. Addition of 50 FM EPTC, in general, did not alter amounts of [14C]MG-191 taken up. Initial translocation of radiolabel from roots to shoots was more rapid at 10 ,uM [14C]MG-191 treatment compared to 50 ,uM. EPTC had no effect on radiolabel movement at either safener rate. MG-191 was metabolized rapidly to water-soluble metabolites. Slower formation of water-soluble products was detected only during the initial 3 h in the presence of EPTC. Also, thin-layer chromatographic analyses of waterand hexane-soluble metabolite fractions confirmed rapid transformation of the parent molecule. Because addition of EPTC retarded parent MG-191 metabolism 3 h after treatment, we assume that initial availability of the MG-191 molecule may be prerequisite to its protective effect. Nomenclature: MG-191, 2-dichloromethyl-2-methyl1,3-dioxolane; EPTC, S-ethyl dipropylthiocarbamate; corn, Zea mays L. 'Pioneer 3737.' Additional index words: MG-191, EPTC, safener.