Panoramic chemical imaging of opium alkaloids in Papaver somniferum by TOF-SIMS

Abstract

Accurate mapping of opium alkaloids in Papaver somniferum (P. somniferum) is significant for comprehensively elucidating their biosynthetic pathways and metabolic regulations. Here we describe a panoramic chemical imaging strategy based on time-of-flight secondary ion mass spectrometry (TOF-SIMS) that enables a thorough and precise visualization of the spatial differentiation of five opium alkaloids (morphine, codeine, thebaine, papaverine and noscapine) in P. somniferum. Notably, the opium alkaloids exhibited enrichment in the capsule, pistil, receptacle and peduncle. Moreover, a series of cross sections of a capsule were imaged to reveal a three-dimensional horizon of internal distribution of opium alkaloids. Opium alkaloids were observed enriched within the pseudoseptum and the “tube-like” structure of the inner pod wall, witnessing a downward trend toward the stigmatic disk. Finally, in high spatial resolution mode of TOF-SIMS, direct single-cell level chemical mapping of opium alkaloids in the phloem of the vascular bundles of P. somniferum receptacle was achieved for the first time. The introduced imaging strategy can provide multi-dimensional insights into the spatial distribution of opium alkaloids in P. somniferum, and the findings are expected to facilitate shedding light on the biological activities of these pharmacologically valued alkaloids.