Mechanism for the Differential Translocation of Amiben in Plants

The proportion of the total plant radioactivity present in shoots at the end of a 24-hour exposure of the roots to 0.5 milligram per liter (14)C-3-amino-2,5-dichlorobenzoic acid ((14)C-amiben) ranged from 1.4 to 74.3% in 13 species. When roots of 10-day-old wheat (Triticum aestivum L. em. Thell., Triumph) and 13-day-old barnyard grass (Echinochloa crusgalli L. Beauv.) plants were treated with 0.5 milligram per liter (14)C-amiben for 12 or 24 hours, barnyard grass shoots contained at least eight times more of the total plant radioactivity than did wheat shoots. In similar experiments with (14)C-2-chloro-4-(ethylamino)-6-(isopropylamine)-s-triazine ((14)C-atrazine), there were no differences in translocation between these two species.The rates of (14)C-amiben absorption into the plants and translocation to shoots in both species were constant with time for 10 hours. When the bases of excised shoots were exposed to (14)C-amiben, both species transported the radioactivity into leaves and metabolized the amiben similarly to intact shoot tissues. Amiben was the only radioactive compound identified in guttation fluid obtained from (14)C-amiben-treated barnyard grass. When treated for 10 hours with (14)C-amiben at concentrations of 0.05 to 200.0 milligrams per liter, a significant correlation between log [shoot amiben] (in amiben equivalents) and log [root amiben concentration] was obtained with no species differences.The postulated mechanism for the species differences in (14)C-amiben translocation is that the tolerant species, wheat, fixes the (14)C-amiben in the roots, principally as nontransportable N-(carboxy-2,5-dichlorophenyl)glycosylamine (N-glucosyl amiben), while only "free" amiben is translocated to shoots. Wheat converted more absorbed amiben to N-glucosyl amiben or amiben-X than barnyard grass in both roots and shoots.The amiben concentration required to inhibit radicle elongation 50% in 4-day-old seedlings was about 50 milligrams per liter for wheat and 1 milligram per liter for barnyard grass.