Spatially resolved detection of small molecules from press-dried plant tissue using MALDI imaging.

Abstract

Matrix-assisted laser desorption/ionization imaging mass-spectrometry (MALDI-IMS) is a chemical imaging method that can visualize spatial distributions of different molecules. Previous work on imaging plant tissue has mainly focused on cryosectioned tissue samples, which is a valuable sample preparation methodology, but cannot be applied to thin, delicate samples, such as flower petals. Previous work focused on imaging unsectioned tissue has suffered from difficulties in extracting metabolites to the surface where they mix with the matrix, namely due to the waxy lipid surface layer. In this work, we use established delipidation techniques combined with a solvent vapor extraction prior to matrix application, while applying the matrix as many low-concentration sprays. Using this procedure, we have imaged tissue from various plant species and observed a wide range of plant-specific small molecules with varying levels of localization to specific portions of the tissue samples. This work demonstrates the applicability of MALDI-IMS to press-dried herbarium samples without freezing or cryosectioning.