MODE OF ACTION OF THIOCYANATES AND IODIDES IN AMINOTRIAZOLE FORMULATIONS

Ammonium thiocyanate (I) was shown to inhibit the oxidation of aminotriazole (3‐amino‐1,2,4‐triazole) in two free‐radical generating systems: (a) riboflavin photo‐sensitised oxidation; and (b) oxidation by hydroxyl radicals. Evidence from in‐vitro studies is presented to show that I could enhance aminotriazole performance by being preferentially oxidised within the leaf, thereby preventing aminotriazole free‐radical formation and subsequent conjugation with amino acids and other compounds. This opens up the possibility of a whole new range of additives which could enhance translocation by inhibiting free‐radical reactions. A comparison of possible inhibitors revealed that cyanides, iodides and perhaps bromides may be of use in this respect. In addition to inhibiting free‐radical reactions, I and potassium iodide (II) were shown to have a considerable effect on the uptake of aminotriazole by bean leaves (Phaseolus vulgaris var. Canadian Wonder). In the absence of additives, uptake of aminotriazole was negligible (1.8%); in the presence of a 1:1 molar ratio of I or II, uptake of aminotriazole was increased to 36.6% and 54.2% respectively. At a 3:1 molar ratio of additive:aminotriazole, the respective figures were 63.5% and 81.0%. II appeared to be the more efficient of the two additives at higher humidity. However, the results and observations indicated that the situation may be reversed under low‐humidity conditions. Copyright © 1979 John Wiley & Sons, Ltd