Purification and Partial Characterization of a Glucan Containing Indole-3-acetic Acid

Abstract

The "bound auxin" of Zea mays, first described by Berger and Avery (Amer. J. Bot. 1944; 31: 199-203) has been purified and partially characterized. It is an indole-3-acetic acidcontaining, high molecular weight, lipophilic cellulosieglucan. The indole-3-acetic acid is in ester linkage as evidenced by indoleacetamide formation upon ammonolysis. The glucan is of variable chain length and comprises, in general, 35 to 50 per cent of the dry weight of the compound. The glucosidic residues are ,8 1 -e 4 linked and are hydrolyzed by cellulase. Mild acid hydrolysis produces cellobiose and cellotriose. Other components, as yet unidentified, of the compound are described.Recent studies from this laboratory have been concerned with the characterization of the low molecular weight, watersoluble compounds of IAA isolated from the kernels of Zea mays (4,12,13,15,(25)(26)(27). These compounds, designated the B compounds by Labarca et al. (13), comprise almost one-half of the total indolylic compounds of corn and were found to be esters of IAA and either myoinositol or myoinositol glycosides. The remaining approximately one-half of the esterified IAA, the A fraction of Labarca et al. (13), has not been intensively studied in recent years. This, apparently high molecular weight and lipid-soluble fraction, was the original "bound auxin" of Berger and Avery (3, 5) and 9). These workers demonstrated that hydrolysis of the bound auxin by alkali or by passage through the human digestive tract led to the liberation of free IAA. This earlier work was confirmed and extended by Hemberg (11), Hamilton et al. (10), Labarca (12) and by Takano et al. (23). Collectively these workers demonstrated that the A fraction was probably of high molecular weight and that subsequent to alkaline hydrolysis, IAA was obtained from the fraction.We wish, in the present work, to describe methods for purification of the A fraction; to present evidence that the A-compound is an ester of IAA and a glucan of variable numbers of glucose residues; to present some properties of components of the compound other than IAA and glucan; and to demonstrate that the glucan is a cellulosic polysaccharide containing / 1 ->

Esters of Indole-3-Acetic Acid from Avena Seeds

“…This was further confirmed for the pH 4.7 ester fraction by GLC. Similar results were obtained in the characterization of the high mol wt IAA ester fraction isolated from corn kernels (21). Thus, the carbohydrate portions of the oat IAA ester fractions, and of the high mol wt corn IAA ester fraction (2 1).…”

“…as yet. unidentified substances (21). The Avena IAA esters are, thus, analogous to the Zea A fraction, but differ in being water-soluble and precipitable from water by 50% or more acetone or alcohol.…”

“…The ester fraction peptides contained approximately 12% serine residues which could serve as the point of attachment for carbohydrate. The high mol wt IAA ester from Zea did not contain protein (21).…”

Concentration and Metabolic Turnover of Indoles in Germinating Kernels of Zea mays L.

“…Knowledge of pool size and rate of pool turnover has permitted: (a) identification of indole-3-acetyl-myo-inositol as the major chemical form for transport of indole-3-acetic acid (IAA) from endosperm to shoot; (b) demonstration that the free IAA of the endosperm is turning over rapidly with a half-life of 3.2 hours; (c) identification of esters of IAA as the immediate precursors of IAA in the endosperm and shoot-, (d) demonstration that neither tryptophan nor tryptamine is a major precursor of IAA for the seed or shoot-, (e) identification of IAA-myo-inositol glycosides as precursors of IAA-myo-inositol.It is concluded that seedlings of Zea mays utilize esters of IAA, and not tryptophan or its derivatives, for the IAA requirements of the germinating seedling.The endosperm of kernels of Zea mays contains small amounts of indole-3-acetic acid and large amounts of esterified IAA (5,15,26,27,35,38). The esterified IAA has been chemically characterized (1,21,26,36) and assayed quantitatively in the dry seed (35) and during ripening (9 and unpublished data) and during germination of the kernels (ref.…”

“…The endosperm of kernels of Zea mays contains small amounts of indole-3-acetic acid and large amounts of esterified IAA (5,15,26,27,35,38). The esterified IAA has been chemically characterized (1,21,26,36) and assayed quantitatively in the dry seed (35) and during ripening (9 and unpublished data) and during germination of the kernels (ref.…”