Metribuzin Absorption and Translocation in Two Barley (Hordeum vulgare) Cultivars

Root and foliar absorption and translocation of14C-metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] were determined in tolerant (‘Steptoe’) and susceptible (‘Morex’) barley (Hordeum vulgareL.) cultivars grown in nutrient solution culture under greenhouse conditions. Root-applied metribuzin toxicity to the two barley cultivars was also examined. A 50% reduction in growth occurred at 0.22 and 0.72 μM metribuzin for Morex and Steptoe, respectively. Root absorption was similar for both cultivars at 1 day, but Steptoe absorbed about two times more metribuzin 4 and 8 days after application than did Morex. Steptoe absorbed 19% of the total applied metribuzin by 8 days. Root absorption was positively correlated with water uptake (r≥ 0.87). Leaf absorption was three times greater for Morex than for Steptoe after 4 days. Transport to leaves from root application was rapid, and, by 1 and 8 days, leaves of Steptoe contained 71 and 82% and leaves of Morex 78 and 84% of the total absorbed14C, respectively. Translocation was apoplastic following both root and leaf absorption and was similar for both cultivars. Differential tolerance could partially be accounted for by differences in foliar absorption but not by differences in root absorption.