Abstract
Plants produce IAA from the TRP-dependent and -independent pathways. In Arabidopsis, the TRP-dependent pathway involves at least two metabolic routes; the indole glucosinolate and tryptamine pathways. Here, we have developed new isotope labeling systems to assess contribution of the TRP-dependent pathway to IAA biosynthesis in Arabidopsis. The intermediates of the TRP-dependent pathway were efficiently 15N-labeled by a feeding of [15N2]TRP to the seedlings of Arabidopsis trp1-1 mutant. Similarly, the tryptamine pathway was selectively 15N-labeled using Arabidopsis trp3-1 mutant. Our LC-MS/MS and GC-MS data indicated that IAA is moderately produced from the TRP-dependent pathway, but the tryptamine pathway does not largely contribute to IAA biosynthesis at whole-plant level. We are currently analyzing the contribution of the tryptamine pathway to IAA biosynthesis at organ/tissue levels.
