Application of Mass Spectrometry Imaging in Evaluating the Spatial Distribution of Aminoacids and Sugars in Basil Leaves upon Long-Time Exposure to Cadmium

Basil samples (Ocimum basilicum Lameaceae) were exposed to cadmium and analyzed on porous PTFE membrane, and TLC plate substrates by desorption electrospray ionization mass spectrometry imaging (DESI-MSI) for amino acids and sugars identification. The TLC plate was the best substrate for analysis of the basil leaves, with high-definition images, small extract scattering, low mass deviations, and excellent reliability in the spatial distribution of the analytes. DESI-MSI analysis identified 13 images of ions putatively annotated as amino acids and sugars with high accuracy (mass deviation between -1.97 to 1.42 ppm) in contaminated and non-contaminated leaves. In general, the amino acids and sugars (proline, histidine, glutamine, arginine, homoarginine, theanine, hexose sugars, and disaccharides) accumulated preferably in basil leaves as a defense mechanism against exposure to cadmium. Asparagine, tyrosine, glutamic acid, and phenylalanine were inhibited when exposed to the toxic element. The images obtained in this study demonstrated the spatial distribution and accumulation of amino acids and sugars in basil leaves as a response to cadmium contamination, confirming that DESI-MSI is a valuable and promising tool for metabolomics studies in plants exposed to toxic metals.