Ammonium Sulfate Enhancement of Picloram Absorption by Detached Leaves

Ammonium sulfate increased the magnitude and rate of 14C-picloram (4-amino-3,5,6-trichloropicolinic acid) absorption in detached strawberry guava (Psidium cattleianum Sabine) leaves. Absorption of 14C-picloram with or without ammonium sulfate leveled off at 6 to 12 hr. The magnitude of the ammonium sulfate-induced increase in 14C-picloram absorption was not affected by picloram concentration in the range 250 to 2000 ppmw, or by leaf age. The absorption of 14C-picloram was increased by 0.1, 0.5, 1.0, and 10% ammonium sulfate; 0.01% had no effect. Increased 14C-picloram absorption resulted from adding the ammonium salts of sulfate, nitrate, chloride, or dibasic phosphate, but ammonium sulfate was the only one of six sulfate salts to increase picloram absorption. A pH adjustment of the external solution from 6 to 4 increased picloram absorption, whereas a pH change from 6 to 8 had no effect. Both ammonium dibasic phosphate at a solution pH of 7.7 and ammonium monobasic phosphate at pH 4.6 increased picloram absorption, whereas potassium dibasic phosphate at pH 9.5 had no effect, and potassium monobasic phosphate at pH 4.6 did increase absorption.