Choline conjugates of auxins. I. Direct evidence for the hydrolysis of choline-auxin conjugates by pea cholinesterase

We synthesized the choline conjugates of three derivatives of phenylacetic acid, four derivatives of phenoxyacetic acid, and of naphthalene-1-acetic acid and measured the effects of these conjugates on pea (Pisum sativum L. cv. Alaska) stem segment elongation. We also synthesized the thioester analogs of six choline conjugates and measured their rates of hydrolysis by pea cholinesterase and their rates of spontaneous hydrolysis. With one exception, conjugates that stimulated growth were hydrolyzed at high rates by pea cholinesterase, while conjugates that were hydrolyzed at low rates by pea cholinesterase did not stimulate growth. The results are consistent with a model in which cholinesterase releases active auxins from these conjugates.