The acquisition of thin sections of açaí (Euterpe oleracea Mart.) seed with elevated potassium content for molecular mapping by mass spectrometry imaging

Abstract

RationaleMatrix‐assisted laser desorption/ionization imaging mass spectrometry (MALDI‐IMS) of tissues became popular in the last decade. Consequently, adapting sample preparation methods for different materials turned out to be a pivotal step for successful analysis due to the requirement of sample slices of 12–20 μm thickness. However, acquiring thin sections compatible with MALDI‐IMS for unusual samples is challenging, as existing histological protocols may not be suitable, thus requiring new methods. Açaí (Euterpe oleracea Mart.) seed is an example of a challenging material due to its toughness and resistance to crack, therefore our goal was to develop a methodology to obtain thin (12–20 μm) and entire sections of açaí seeds for MALDI‐IMS analysis.MethodsDifferent strategies were evaluated for obtaining thin sections of seeds, and the combination of the following steps was found to be the most suitable option: (i) softening of seeds by water immersion for 24 h; (ii) transversal cut of seeds to obtain half‐seeds using a razor blade and a hammer; (iii) half‐seeds imbibition in gelatin; (iv) samples sectioning using a cryostat at −20°C to obtain samples with 12–20 μm thickness; (v) collection of samples in an indium tin oxide‐coated glass slide covered by double‐sided copper tape to avoid sample wrapping and ensure adhesion after unfreezing; and (vi) storage of samples in a −80°C freezer, if necessary.ResultsThis adapted sample preparation method enabled the analysis of açaí seeds by MALDI‐IMS, providing spatial distribution of carbohydrates in the endosperm.ConclusionsThe adaptations developed for sample preparation will help investigate the metabolic and physiological properties of açaí seeds in future studies.