Analysis of Indole-3-acetic Acid Metabolism in Zea mays Using Deuterium Oxide as a Tracer

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Abstract
A method using deuterium oxide (D2O) as a tracer was used to study indole-3-acetic acid (IAA) metabolism in Zea mays seedlings. Seeds were imbibed and grown for 4 days in 30% D2O in the dark. IAA was then isolated from roots and shoots and analyzed for deuterium content by mass spectrometry. We found that a significant portion of the IAA isolated from plants had incorporated deuterium at nonexchangeable sites of the indole ring. This indicates that some of the IAA in the germinating seedling is made via de novo indole synthesis. Moreover, we found that the deuterium content of IAA was 2.6 times greater in shoots than in roots. These results indicate that at least some of the IAA in roots and shoots came from different biosynthetic pathways. It appears that the fraction of IAA produced via de novo indole synthesis is greater in shoots than in roots.