Micropropagation with 3-methyleneoxindole: Its obligatory role in indole-3-acetic acid-mediated auxin action

Summary 3-Methyleneoxindole (MO), a metabolite of the plant auxin indole-3-acetic acid (IAA), was more active than IAA in supporting Stage II and III micropropagation of several plant species. In Stage II micropropagation, characterized by the rapid numerical increase of shoots, the optimal IAA concentration was 0.01 mM compared to 0.1 mM MO for most plants. In Stage III micropropagation where auxin is required for the rhizogenic response, 0.1 μM MO was more effective than 0.01 mM IAA. Inhibition analysis of plant growth with chlorogenic acid (CGA) suggested an obligatory role for MO in IAA-mediated auxin reactions: CGA, which blocks the enzymatic oxidation of IAA to MO, in vivo, completely abolished IAA's ability to support the growth of explants during micropropagation. In contrast, CGA did not inhibit the auxin activity of MO, the product of the blocked reaction. The growth rate and rooting efficiency of tobacco propagules in Stage III medium was improved substantially if these were first exposed to a high concentrations of MO and subsequently transferred to media containing low or no MO.