Interaction of Indoleacetic Acid with Its Inositol and Glucoside Conjugates in Avena Coleoptile Curvature

Avena coleoptile curvature is promoted by indoleacetic acid (IAA) IAA-glucoside, and IAA-inositol when these substances are applied in agar to the decapitated apical end of deseeded plantlets. Absorption of [(3)H]IAA-inositol over a wide range of concentrations during the 20 hour period of incubation is only 20 to 50% of the applied amount, compared with 85 to 92% of uptake of the applied [(3)H]IAA at equimolar concentrations. The absorption of IAA-glucoside could not be readily measured. The stimulation by both IAA-conjugates is very similar to that of free IAA at low concentrations (0.2 and 0.4 micromolar), but much less at higher concentrations. The interaction of free IAA with IAA-glucoside is additive or synergistic (depending on concentration). The interaction of free IAA with IAA-inositol is an inhibition (i.e. less than additive). The simultaneous application of equimolar concentrations of free IAA does not change the chromatographic pattern of the metabolic products of [(3)H] IAA-inositol. One of the more polar metabolites of [(3)H]IAA-inositol has chromatographic characteristics similar to the major polar metabolite of free [(3)H]IAA on an isocratically eluted reversed phase C(18) high performance liquid chromatography system that separates a number of IAA sugar and amino acid conjugates from each other, and from free IAA.