Metabolism of Indoleacetic Acid in Rust Diseases. II. Metabolites of Carboxyl-labeled Indoleacetic Acid in Tissues

Abstract

A quantitative comparison was made of metabolites formed by normal and rust-affected 1st leaves of wheat supplied carboxyl C14-labeled indoleacetic acid. In 6 hours, normal mature wheat leaves converted approximately 60% of exogenous indoleacetic acid into 4 radioactive water-soluble components. In the same time period, decarboxylation reactions accounted for degradation of only 20% of supplied indoleacetic acid. Since only indoleacetic acid was found in the bathing solution and no appreciable radioactivity was observed in organic acids, it is concluded that wheat tissue has pathways for metabolism of exogenous indoleacetic acid which can be quantitatively more significant than decarboxylation. Although 3 of the compounds (A1, A2, A3) had identical Rf values in isopropanol-ammonia-water (101:1) and migrated with indoleacetylaspartic acid, chromatography in other solutions indicated that all were distinct and not identical to indoleacetylaspartic acid. The 4th component, B, migrated as indoleacet-amide in isopropanol-ammonia-water but not in other solvents. Comparison of the rates of formation at intervals of 2 hours indicates that A1, A2, and A3 are formed at faster rates than either B or the CO2 resulting from decarboxylation. The latter 2 reactions had rates which were comparable. In rust-affected wheat leaves, accumulation of radioactivity in tissue and decarboxylation of indoleacetic acid were lower than in healthy tissues especially in the last 4 hours of exposure. Compound B was not found in diseased tissue and the amounts of A1, A2, and particularly A3 were reduced. Although the data are too meager for analysis of the complex reactions controlling uptake and metabolism, it is suggested that reduced uptake of indoleacetic acid may be responsible for the low rate of destruction via decarboxylation in diseased tissue.