Hormonal control of myo-inositol incorporation into pectin.

The rate of incorporation of glucose into the galacturonic acid residues of pectin has been shown to be modified by the auxin, indoleacetic acid (1). In recent experiments, Loewus, Kelly, and Neufeld (2, 3) have shown that myo-inositol is also a good precursor of the uranic acid of pectin. These workers suggest that myo-inositol is oxidatively cleaved to form glucuronic acid. The latter might be transformed into uriclme diphosphate galacturonic acid, which, by analogy to the synthesis of other polysaccharides, is a logical precursor of pectin (4). Evidence delineating the actual biosynthetic pathway of pectin is yet to be obtained. The experiments described in this communication were designed to compare the rate of myo-inositol incorporation into the galacturonic acid residues of pectin with a similar rate previously determined for glucose. We have also investigated the ability of indoleacetic acid to control this incorporation. Our purpose was to determine whether glucose and myo-inositol have a common precursor during their transformation to the galacturonide of pectin, and if so, whether the plant hormone controls the synthesis of pectin prior to or following the formation of this compound.