LC-MS/MS versus TLC plus GC methods: Consistency of glycerolipid and fatty acid profiles in microalgae and higher plant cells and effect of a nitrogen starvation
Résumé
Methods to analyze lipidomes have considerably evolved, more and more based on mass
spectrometry technics (LC-MS/MS). However, accurate quantifications using these methods
require 13C-labeled standards for each lipid, which is not feasible because of the very
large number of molecules. Thus, quantifications rely on standard molecules representative
of a whole class of lipids, which might lead to false estimations of some molecular species.
Here, we determined and compared glycerolipid distributions from three different types of
cells, two microalgae (Phaeodactylum tricornutum, Nannochloropsis gaditana) and one
higher plant (Arabidopsis thaliana), using either LC-MS/MS or Thin Layer Chromatography
coupled with Gas Chromatography (TLC-GC), this last approach relying on the precise
quantification of the fatty acids present in each glycerolipid class. Our results showed that
the glycerolipid distribution was significantly different depending on the method used. How
can one reconcile these two analytical methods? Here we propose that the possible bias
with MS data can be circumvented by systematically running in tandem with the sample to
be analyzed a lipid extract from a qualified control (QC) of each type of cells, previously analyzed
by TLC-GC, and used as an external standard to quantify the MS results. As a case
study, we applied this method to compare the impact of a nitrogen deficiency on the three
types of cells.
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