Free IAA Levels Research Articles

Effects of phenolic substances on metabolism of exogenous indole‐3‐acetic acid in maize stems

AbstractFour‐day‐old stem segments of Zea mays L. cv. Seneca 60 were treated sequentially with phenolic substances and indole‐3‐acetic [2‐14C] acid ([2‐14C]IAA). Formation of bound IAA was rapid, but a pretreatment with p‐coumaric acid, ferulic acid or 4‐methylumbelliferone decreased the level of bound IAA. The decrease is not likely related to the effect of the phenolics on enzymic oxidation of IAA, since the level of free IAA was not limiting and the activity of ferulic acid in enzymic oxidation of IAA is different from that of p‐coumaric acid and 4‐methylum‐belliferone. Apparently these compounds inhibited the formation of bound IAA and consequently caused an accumulation of free IAA. In contrast, caffeic acid, protocatechuic acid and 2,3‐dihydro‐2, 2‐dimethyl‐7‐benzofuranol had little effect.After the uptake of IAA there was a slow but steady incorporation of the radioactivity into the 80% ethanol‐insoluble, 1 M NaOH‐soluble fraction. Phenolic substances also affected this process. The compounds which are cofactors of IAA‐oxidase increased the incorporation while those which are inhibitors of IAA‐oxidase decreased the incorporation. Results suggest that the phenolics also affected the enzymic oxidation of IAA in vivo in the same way as in vitro.

The transport and metabolism of 14C-labelled indoleacetic acid in intact pea seedlings

Part of the IAA-I- or IAA-2-(14)C applied at low concentrations to the apices of intact, light-grown dwarf pea seedling was transported unchanged to the root system The calculated velocity of transport in the stem was 11 mm per hour. In the root the label accumulated in the developing lateral root primordia.A large proportion of the applied IAA was converted by tissues of the apical bud, stem and root to indole-3-acetyl-aspartic acid (IAAsp). This compound was not transported. In addition evidence was obtained for the formation of IAA-protein complexes in the apex and roots, but not in the fully-expanded internodes.Large quantities of a decarboxylation product of IAA, tentatively indentified as indole-3-aldehyde (IAld), and several minor metabolites of IAA, were detected in extracts of the roots and first internodes, but not in the above-ground organs exposed to light. These compounds were readily transported through stem and root tissues. Together, the decarboxylation of IAA and the formation of IAAsp operated to maintain a relatively constant level of free IAA-(14)C in the root system.