The metabolome of an oak tree root colonized by an ectomycorrhizal fungus by FT-ICR-MS analysis

The metabolome of mycorrhizal cork oak (Quercus suber L.) roots colonized by the ectomycorrhizal fungus Pisolithus tinctorius was analysed by Fourier Transform Ion Cyclotron Resonance mass spectrometry (FT-ICR-MS). Samples from mycorrhizal and non-mycorrhizal (control) roots were extracted using mixtures of water, methanol and chloroform. Before analysis, samples were diluted 1000-fold and leucine enkephalin was added to be use for internal calibration of each sample spectrum ([M+H]⁺ = 556.276575 Da or [M-H]^- = 554.260925 Da). Extracts from each sample were analysed by direct infusion in an Apex Qe 7-Tesla Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FTI-CR-MS, Brüker Daltonics). Spectra were acquired using electrospray ionization (ESI) in positive (ESI⁺) and negative (ESI^-) modes. Mass spectra were recorded with an acquisition size of 512k, in the 100 to 1000 m/z mass range. Mass spectra were analysed using the software package Data Analysis 5.0 (Brüker Daltonics, Bremen, Germany). Single point calibration was performed with the leucine enkephalin standard, both in positive and negative ionization modes. Mass peak lists (m/z and intensities) were exported at a signal-to-noise ratio of 4.