Comprehensive metabolome characterization of leaves, internodes, and aerial roots of Vanilla planifolia by untargeted LC–MS and GC × GC–MS

Introduction: Untargeted metabolomics is a powerful tool that provides strategies
for gaining a systematic understanding of quantitative changes in the levels of metabolites,
especially when combining different metabolomic platforms. Vanilla is one of
the world's most popular flavors originating from cured pods of the orchid Vanilla planifolia.
However, only a few studies have investigated the metabolome of
V. planifolia, and no LC–MS or GC–MS metabolomics studies with respect to leaves
have been performed.
Objective: The aim of the study was to comprehensively characterize the metabolome
of different organs (leaves, internodes, and aerial roots) of V. planifolia.
Material and Methods: Characterization of the metabolome was achieved using two
complementary platforms (GC GC–MS, LC-QToF-MS), and metabolite identification
was based on a comparison with in-house databases or curated external spectral
libraries.
Results: In total, 127 metabolites could be identified with high certainty (confidence
level 1 or 2) including sugars, amino acids, fatty acids, organic acids, and amines/
amides but also secondary metabolites such as vanillin-related metabolites, flavonoids,
and terpenoids. Ninty-eight metabolites showed significantly different intensities
between the plant organs. Most strikingly, aglycons of flavonoids and vanillinrelated
metabolites were elevated in aerial roots, whereas its O-glycoside forms
tended to be higher in leaves and/or internodes. This suggests that the more bioactive
aglycones may accumulate where preferably needed, e.g. for defense against
pathogens.
Conclusion: The results derived from the study substantially expand the knowledge
regarding the vanilla metabolome forming a valuable basis for more targeted investigations
in future studies, e.g. towards an optimization of vanilla plant cultivation.