Silver Nanoparticle-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging of Low-Molecular-Weight Compounds in a Narcissus Bulb.

Surface-assisted laser desorption/ionization mass spectrometry imaging (SALDI-MSI) using steel target coated with silver nanoparticles (AgNPs) by electrodeposition was applied for the direct visualization of metabolites in bulb tissue of Narcissus pseudonarcissus. Fresh bulb cross-sections were transferred onto an AgNP-SALDI target by a simple tissue imprint procedure and analyzed using a MALDI TOF mass spectrometer operating in positive-ion reflectron mode. Ion images were generated after total ion current normalization and metabolite annotation was performed based on accurate mass measurements, characteristic silver adduct formation, database searches and literature data. Twenty-one ion images representing seventeen putatively annotated metabolites were selected for detailed discussion. The putatively annotated compounds included primary metabolites (histidine, malic acid, succinic acid, thiamine, coenzyme A and acetyl-coenzyme A), phytohormones (indole-3-acetic acid, indole-3-butyric acid, 3-indolepropionic acid, 4-chloroindole-3-acetic acid and abscisic acid), flavonoids and characteristic Amaryllidaceae alkaloids, including galanthamine, lycoramine, crinine, assoanine, habranthine and 5,6-dihydrobicolorine. Distinct spatial distributions were observed for individual metabolites, reflecting the metabolic heterogeneity of bulb tissues. The results demonstrate that AgNPs-SALDI-MSI provides a rapid, matrix-free approach for in situ visualization of low-molecular-weight metabolites in plant tissues while preserving their spatial organization, making it a promising tool for plant metabolomics and phytochemical investigations.