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

RATIONALE

Matrix-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.

METHODS

Different strategies were evaluated for obtaining thin sections of seeds, being the combination of the following steps 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; and (v) collection of samples in an indium tin oxide coated glass slide covered by a double-sided copper tape to avoid sample wrapping and ensure adhesion after unfreezing; (iv) storage of samples in a -80 °C freezer, if necessary.

RESULTS

As a result, this adapted sample preparation method enabled the analysis of açaí seeds by MALDI-IMS providing spatial distribution of carbohydrates in the endosperm.

CONCLUSIONS

The adaptations developed for sample preparation will help investigate the metabolic and physiological properties of açaí seeds in future studies.