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Mechanism for the Differential Translocation of Amiben in Plants ¹

^a Crops Research Division, Agricultural Research Service, United States Department of Agriculture, Department of Agronomy, University of Illinois, Urbana, Illinois 61801

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 ¹⁴C-3-amino-2,5-dichlorobenzoic acid (¹⁴C-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 ¹⁴C-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 ¹⁴C-2-chloro-4-(ethylamino)-6-(isopropylamine)-s-triazine (¹⁴C-atrazine), there were no differences in translocation between these two species.

The rates of ¹⁴C-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 ¹⁴C-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 ¹⁴C-amiben-treated barnyard grass. When treated for 10 hours with ¹⁴C-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 ¹⁴C-amiben translocation is that the tolerant species, wheat, fixes the ¹⁴C-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.