School of Plant Science, University of Tasmania, Hobart, Tasmania 7001, Australia.
Plant Physiol. 2010 Dec;154(4):1957-65. doi: 10.1104/pp.110.165803. Epub 2010 Oct 25.
The tryptamine pathway is one of five proposed pathways for the biosynthesis of indole-3-acetic acid (IAA), the primary auxin in plants. The enzymes AtYUC1 (Arabidopsis thaliana), FZY (Solanum lycopersicum), and ZmYUC (Zea mays) are reported to catalyze the conversion of tryptamine to N-hydroxytryptamine, putatively a rate-limiting step of the tryptamine pathway for IAA biosynthesis. This conclusion was based on in vitro assays followed by mass spectrometry or HPLC analyses. However, there are major inconsistencies between the mass spectra reported for the reaction products. Here, we present mass spectral data for authentic N-hydroxytryptamine, 5-hydroxytryptamine (serotonin), and tryptamine to demonstrate that at least some of the published mass spectral data for the YUC in vitro product are not consistent with N-hydroxytryptamine. We also show that tryptamine is not metabolized to IAA in pea (Pisum sativum) seeds, even though a PsYUC-like gene is strongly expressed in these organs. Combining these findings, we propose that at present there is insufficient evidence to consider N-hydroxytryptamine an intermediate for IAA biosynthesis.
色胺途径是吲哚-3-乙酸 (IAA) 生物合成的五个提议途径之一，IAA 是植物中的主要生长素。据报道，AtYUC1（拟南芥）、FZY（番茄）和 ZmYUC（玉米）等酶能够催化色胺转化为 N-羟基色胺，这是色胺途径中 IAA 生物合成的限速步骤。这个结论是基于体外测定，然后进行质谱或 HPLC 分析得出的。然而，反应产物的质谱报告之间存在重大不一致。在这里，我们提供了真实的 N-羟基色胺、5-羟色胺（血清素）和色胺的质谱数据，以证明至少一些已发表的 YUC 体外产物的质谱数据与 N-羟基色胺不一致。我们还表明，色胺在豌豆（Pisum sativum）种子中不会代谢为 IAA，尽管这些器官中强烈表达了类似 PsYUC 的基因。结合这些发现，我们提出目前没有足够的证据将 N-羟基色胺视为 IAA 生物合成的中间产物。
