Abstract
The plant hormone abscisic acid (ABA) and the jasmonic acid related-compound 12-oxo-phytodienoic acid (OPDA) play crucial roles in seed development, dormancy, and germination. However, a lack of suitable techniques for visualising plant hormones has restricted the investigation of their biological mechanisms. In the present study, desorption electrospray ionisation-imaging mass spectrometry (DESI-IMS), a powerful tool for visualising metabolites in biological tissues, was used to visualise ABA and OPDA in immature Phaseolus vulgaris L. seed sections. The mass spectra, peak values and chemical formulae obtained from the analysis of seed sections were consistent with those determined for ABA and OPDA standards, as were the precursor and major fragment ions observed in tandem mass spectrometry (MS/MS) imaging. Furthermore, the precursor and fragment ion images showed similar distribution patterns. In addition, the localisation of ABA and OPDA using DESI-IMS was confirmed using liquid chromatography-MS/MS (LC-MS/MS). The results indicated that ABA was mainly distributed in the radical and cotyledon of the embryo, whereas OPDA was distributed exclusively in external structures, such as the hilum and seed coat. The present study is the first to report the visualisation of plant hormones using IMS, and demonstrates that DESI-IMS is a promising technique for future plant hormone research.
Highlights
Plant hormones comprise chemically diverse compounds that occur at low concentrations and regulate growth, development, and responses to external stimuli[1]
The present study describes and quantifies the distributions of abscisic acid (ABA) and oxo-phytodienoic acid (OPDA) in immature P. vulgaris L. seed sections using Desorption electrospray ionisation (DESI)-Imaging mass spectrometry (IMS) coupled to a Q-TOF mass spectrometer and LC-ESI-MS/MS analysis
The ABA and OPDA contents of immature seeds are thought to change during development[8,10,12]
Summary
Because efficient sectioning is crucial for successful DESI-IMS analysis[31], we compared a few preparation techniques. When frozen in liquid nitrogen and sectioned at 20-μm thickness, the external structures of immature seeds, such as the hilum and seed coat, were destroyed. Using the Q-TOF, we initially measured ABA and OPDA standards using DESI-MS in the negative ion mode at 30 000 full width at half maximum (FWHM) mass resolution. Both ABA and OPDA were detected as [M-H]− ions. This was followed by DESI-IMS analysis of immature seed sections (Fig. 2a). The ion images at m/z 263.128 (Fig. 2c) and m/z 291.196 (Fig. 2d), together with the merged image of these ions (Fig. 2e), indicated that ABA was mainly distributed in the embryo, including the radicle and cotyledon, whereas OPDA exclusively distributed in external structures, such as the hilum
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