Tissue‐specific metabolite profiling of benzylisoquinoline alkaloids in the root of Macleaya cordata by combining laser microdissection with ultra‐high‐performance liquid chromatography/tandem mass spectrometry

RATIONALE: Tissue-specific metabolite profiling helps to find trace alkaloids masked during organ analysis, which contributes to understanding the alkaloid biosynthetic pathways in vivo and evaluating the quality of medical plants by morphology. As Macleaya cordata contains diverse types of benzylisoquinoline alkaloids (BIAs), the alkaloid metabolite profiling was carried out on various tissues of the root. METHODS: Laser microdissection with fluorescence detection was used to recognize and dissect different tissues from the root of M. cordata. Ultra-high-performance liquid chromatography/quadrupole time-of-flight mass spectrometry was applied to analyze the trace alkaloids in tissues. These detected alkaloids were elucidated using their accurate molecular weights, MS/MS data, MS fragmentation patterns and the known biosynthetic pathways of BIAs. Finally, the distribution of alkaloids in dissected tissues and whole sections was mapped. RESULTS: Forty-nine alkaloids were identified from five microdissected tissues, and 24 of them were detected for the first time in M. cordata. Some types of alkaloids occurred specifically in dissected tissues. More alkaloids were detected in the cork and xylem vascular bundles which emit strong fluorescence under fluorescence microscopy. Some of the screened alkaloids were intermediates in sanguinarine and chelerythrine biosynthetic pathways, and others were speculated to be involved in the new branches of biosynthetic pathways. CONCLUSIONS: The integrated method is sensitive, specific and reliable for determining trace alkaloids, which is also a powerful tool for metabolite profiling of tissue-specific BIAs in situ. The present findings should contribute to a better understanding of the biosynthesis of BIAs in M. cordata root and provide scientific evidence for its quality evaluation based on morphological characteristics. Copyright © 2016 John Wiley & Sons, Ltd.