Mass Spectrometric Approaches to Study the Metabolism of Jasmonates: Biotransformation of Exogenously Supplemented Methyl Jasmonate by Cell Suspension Cultures of Moringa oleifera
Jasmonic acid (JA) and derivatives play a crucial role in plant adaptation to environmental stress. The exogenous application of methyl jasmonate (MeJA) results in activation of stress-related genes and subsequent production of secondary metabolites. This implies the biotransformation of the hormone into a more active form. In this study, Moringa oleifera cell suspension cultures were treated with 100 μM MeJA. Methanolic cell extracts were analyzed with reverse phase ultrahigh performance liquid chromatography (UHPLC) coupled to a quadrupole time-of-flight high definition mass spectrometer (QTOF–HDMS, with MSE data acquisition). Using a targeted approach for jasmonate profiling, extracted ion chromatograms were generated. MS fragmentation patterns were subsequently derived and molecular formulae calculated from the MS data of each ion. Furthermore, triple quadrupole (QqQ) MS, operated in selected reaction monitoring (SRM) mode, was employed to target masses of interest. In addition to MeJA and JA, three jasmonoyl-amino acids were annotated: jasmonoyl-valine (JA-Val), jasmonoyl-isoleucine/leucine (JA-Ile/Leu), and jasmonoyl-phenylalanine (JA-Phe), based on characteristic precursor and product ions. Furthermore, JA conjugated to a hexose was observed, as well as hydroxylated and carboxylated derivatives of JA-amino acid conjugates. The data point to active metabolism of the externally added MeJA by the M. oleifera cells through biotransformation and bioconversion reactions that can be investigated in depth using advanced mass spectrometric analyses.
Key wordsBioconversion Jasmonic acid Jasmonoyl-amino acids Mass spectrometry Methyl jasmonate Moringa oleifera
The University of Johannesburg and the South African National Research Foundation are acknowledged for fellowship support to CHD and grant support to IAD [grant number 95818]. Dr. PA Steenkamp is thanked for UHPLC–MS analyses, Ms. N Ndolvu for assistance with LC/MS/MS analyses, and Dr. F Tugizimana for assistance with data analysis.
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