Root absorption of 14C-5 (ring)-metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] from hydroponic culture and its subsequent translocation in tolerant (‘Russet Burbank’) and susceptible (‘Chipbelle’) potato (Solanum tuberosum L.) cultivars were measured. Differences in root absorption did not appear to be as important to differential tolerance as did translocation differences. Total available metribuzin absorbed was 6 and 7%, 18 and 29%, and 31 and 45% after 1, 4, and 8 days for Russet Burbank and Chipbelle, respectively. Radioactivity was concentrated in stems, petioles, and leaf veins in the tolerant cultivar, whereas interveinal leaf tissue was the major accumulation site for 14C in the susceptible cultivar. Of the total radioactivity in the plants after 8 days, 82 and 87% were in the foliage for the tolerant and the susceptible cultivar, respectively. Translocation was apoplastic. Metribuzin tolerance by Russet Burbank is due in part to restricted translocation to the leaf blades. A model for differential transport between cultivars is proposed.
