Identification of Metabolites in Basil Leaves by Desorption Electrospray Ionization Mass Spectrometry Imaging after Cd Contamination

Abstract

In this study, basil (Ocimum basilicum L.) seedlings were intoxicated with Cd2+ and cultivated using a 5% v v–1 Hoagland nutrient solution. Desorption electrospray ionization mass spectrometry imaging (DESI-MSI) was used to identify different compounds on basil leaves (without and with 10 μmol L–1 Cd2+). DESI-MSI analysis identified 28 images of ions with high accuracy (mass deviation < 1.8 ppm) in contaminated and uncontaminated leaves. The biomarkers formed due to Cd external stress under controlled laboratory experiments were putatively identified in contaminated leaves as jasmone, hexose sugars, salvigenin, flavonoids (C18H14O7 and C21H22O10), and fatty acyl glycosides (C18H28O9). The accumulation of Cd occurred preferentially in the roots but also on the stems and leaves. The methodology to quantify Cd in basil organs was optimized and validated using an ultrasound-assisted micro-extraction procedure. Limits of detection and quantification were 6 and 17 μg L–1, respectively, with a precision better than 7.5 %, obtained by fast sequential flame atomic absorption spectrometry (FS FAAS). The standard reference material of spinach leaf (SRM NIST 1570a) presented a recovery of 101 ± 8 %. DESI-MSI was for the first time employed to examine the behavior of metabolites in plants maintained under stress conditions by the exposure to high levels of cadmium.