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Articles

Esters of Indole-3-Acetic Acid from Avena Seeds ¹

^a Department of Botany and Plant Pathology, Michigan State University, East Lansing, Michigan 48824

The present studies showed that about 80% of the indole-3-acetic acid extractable from Avena kernels by aqueous acetone was esterified to polymers precipitable by ammonium sulfate and ethanol or acetone. The polymers were positively charged, being adsorbed to cation exchange columns at a pH of 3, or below, and eluted at a pH greater than 4. The polymers were heterogeneous with respect to size, about 5,000 to 20,000 daltons, and charge, exhibiting apparent pK_a values of 4.2 and 4.7. The polymer fractions contained esterified IAA, anthrone-reactive material that liberated glucose upon acid hydrolysis, phenolic compounds, and peptidic material with a high proportion of hydrophobic amino acids. Since the esterified IAA was unstable, establishing polymer purity was not possible, and the designation IAA-glucoprotein fraction was adopted.

Dehusked Avena kernels contained 8 mg/kg total IAA of which 5.5% was free and 94.5% esterified. IAA bound through a peptidic linkage was present, but in only trace amounts.

¹ This work was supported, in part, by Grant GB-40821-X from the National Science Foundation. Journal Article No. 7539 from the Michigan Agricultural Experiment Station. The mass spectrometric facilities are supported by National Institute of Health Grant PHS RR-00480 to Professor C. C. Sweeley.

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