Quantification of sterol lipids in plants by quadrupole time-of-flight mass spectrometry

Vera Wewer,Isabel Dombrink,Katharina Vom Dorp,Peter Dörmann

doi:10.1194/jlr.d013987

Abstract

Glycerolipids, sphingolipids, and sterol lipids constitute the major lipid classes in plants. Sterol lipids are composed of free and conjugated sterols, i.e., sterol esters, sterol glycosides, and acylated sterol glycosides. Sterol lipids play crucial roles during adaption to abiotic stresses and plant-pathogen interactions. Presently, no comprehensive method for sterol lipid quantification in plants is available. We used nanospray ionization quadrupole-time-of-flight mass spectrometry (Q-TOF MS) to resolve and identify the molecular species of all four sterol lipid classes from Arabidopsis thaliana. Free sterols were derivatized with chlorobetainyl chloride. Sterol esters, sterol glycosides, and acylated sterol glycosides were ionized as ammonium adducts. Quantification of molecular species was achieved in the positive mode after fragmentation in the presence of internal standards. The amounts of sterol lipids quantified by Q-TOF MS/MS were validated by comparison with results obtained with TLC/GC. Quantification of sterol lipids from leaves and roots of phosphate-deprived A. thaliana plants revealed changes in the amounts and molecular species composition. The Q-TOF method is far more sensitive than GC or HPLC. Therefore, Q-TOF MS/MS provides a comprehensive strategy for sterol lipid quantification that can be adapted to other tandem mass spectrometers.

Highlights

Glycerolipids, sphingolipids, and sterol lipids constitute the major lipid classes in plants
To study the influence of ion suppression, a dilution series was generated from a crude Arabidopsis leaf lipid extract, and peak signals for sterol lipids were observed in the mass spectrometry (MS) and tandem mass spectrometry (MS/MS) modes of the nanospray quadrupole time-of flight (Q-TOF) mass spectrometer
In contrast to GC-based methods, which usually depend on hydrolyzation and derivatization of complex lipids, nondestructive methods are required for the direct measurements of membrane and storage lipids

Summary

Introduction

Glycerolipids, sphingolipids, and sterol lipids constitute the major lipid classes in plants. Sterol lipids are composed of free and conjugated sterols, i.e., sterol esters, sterol glycosides, and acylated sterol glycosides. Sterol lipids play crucial roles during adaption to abiotic stresses and plant-pathogen interactions. No comprehensive method for sterol lipid quantification in plants is available. Q1 mass spectrometry (Q-TOF MS) to resolve and identify the molecular species of all four sterol lipid classes from Arabidopsis thaliana. The amounts of sterol lipids quantified by Q-TOF MS/MS were validated by comparison with results obtained with TLC/GC. Quantification of sterol lipids from leaves and roots of phosphate-deprived A. thaliana plants revealed changes in the amounts and molecular species composition. Q-TOF MS/MS provides a comprehensive strategy for sterol lipid quantification that can be adapted to other tandem mass spectrometers.—Wewer, V., I. Quantification of sterol lipids in plants by quadrupole time-of-flight mass spectrometry.

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