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. 2017 May 10;22(5):774.
doi: 10.3390/molecules22050774.

Direct Analyses of Secondary Metabolites by Mass Spectrometry Imaging (MSI) from Sunflower (Helianthus annuus L.) Trichomes

Denise Brentan Silva  1   2 , Anna-Katharina Aschenbrenner  3 , Norberto Peporine Lopes  4 , Otmar Spring  5
Affiliations

Direct Analyses of Secondary Metabolites by Mass Spectrometry Imaging (MSI) from Sunflower (Helianthus annuus L.) Trichomes

Denise Brentan Silva et al. Molecules. .

Abstract

Helianthus annuus (sunflower) displays non-glandular trichomes (NGT), capitate glandular trichomes (CGT), and linear glandular trichomes (LGT), which reveal different chemical compositions and locations in different plant tissues. With matrix-assisted laser desorption/ionization (MALDI) and laser desorption/ionization (LDI) mass spectrometry imaging (MSI) techniques, efficient methods were developed to analyze the tissue distribution of secondary metabolites (flavonoids and sesquiterpenes) and proteins inside of trichomes. Herein, we analyzed sesquiterpene lactones, present in CGT, from leaf transversal sections using the matrix 2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxycinnamic acid (CHCA) (mixture 1:1) with sodium ions added to increase the ionization in positive ion mode. The results observed for sesquiterpenes and polymethoxylated flavones from LGT were similar. However, upon desiccation, LGT changed their shape in the ionization source, complicating analyses by MSI mainly after matrix application. An alternative method could be applied to LGT regions by employing LDI (without matrix) in negative ion mode. The polymethoxylated flavones were easily ionized by LDI, producing images with higher resolution, but the sesquiterpenes were not observed in spectra. Thus, the application and viability of MALDI imaging for the analyses of protein and secondary metabolites inside trichomes were confirmed, highlighting the importance of optimization parameters.

Keywords: Helianthus; LDI; MALDI; imaging; mass spectrometry; polymethoxylated flavonoids; sesquiterpene lactones; sesquiterpenes; trichome.

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Conflict of interest statement

The authors have no conflict of interest to declare.

Figures

Figure 1
Figure 1
Sunflower leaf with non-glandular trichomes (NGT), capitate glandular trichomes (CGT) in intercostal areas, and linear glandular trichomes (LGT) along leaf veins.
Figure 2
Figure 2
Structure of polymethoxylated flavones and sesquiterpenes identified from LGT.
Figure 3
Figure 3
MALDI mass spectra (positive ion mode) of sesquiterpene lactone argophyllone B (MW: 378, A) and argophyllin B (MW: 380, B) with different matrix compositions and mass spectra of the matrices.
Figure 4
Figure 4
MALDI-MS/MS image reconstructed with the fragment ion m/z 371 obtained from sodiated ion m/z 401 (argophyllone B) (A) (the arrows indicate the region of capitate glandular trichomes, CGT), its fragmentation pathway (B), and the MS/MS spectrum of argophyllone B (m/z 401 [M + Na]+) (C).
Figure 5
Figure 5
MALDI mass spectra (positive ion mode) of the matrix and linear glandular trichome (LGT) extract (the ions of its constituents are highlighted in red).
Figure 6
Figure 6
LDI mass spectra (negative ion mode) of linear glandular trichome (LGT) extract (without a matrix).
Figure 7
Figure 7
LDI-MS image reconstructed from the ions m/z 329.06, 343.08, 359.08 and 373.09 [M − H]−, highlighting the linear glandular trichome (LGT) (A) and mass spectrum from LDI-MSI (B).
Figure 8
Figure 8
MALDI-MS image reconstructed with the ion m/z 66,500 (positive ion mode) from the central rib epidermis of H. annuus.
See this image and copyright information in PMC

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