Active Transport of Choline Sulfate by Barley Roots

Choline sulfate is a major product of sulfate metabolism in plants (9,13). This sulfate ester accounts for up to one-third of the radioactivity in the soluble organic compounds formed after uptake of radiosulfate by plant roots. The analogous choline phosphate occurs in higher plants and is involved in phosphate transport (8). No similar role for choline sulfate as a carrier for sulfate could be detected, but the uptake of choline sulfate was found to be the result of active transport. Studies on the active transport of choline sulfate by excised barley roots are described in this paper. Barley roots have been widely used in active transport studies and form considerable amounts of choline sulfate. The uptake of this zwitterion was studied over a wide range of concentrations in an attempt to elucidate the nature of its dual uptake mechanism. A number of structural analogues of choline sulfate were synthesized and tested as competitive inhibitors of the active transport of choline sulfate. These inhibitor studies were designed to utilize some of the concepts developed in the course of the intensive investigation of the active surface of acetylcholinesterase (6,18). A preliminary report has appeared (10).