Spatial Mapping of Lipids at Cellular Resolution in Embryos of Cotton

Abstract

Advances in mass spectrometry (MS) have made comprehensive lipidomics analysis of complex tissues relatively commonplace. These compositional analyses, although able to resolve hundreds of molecular species of lipids in single extracts, lose the original cellular context from which these lipids are derived. Recently, high-resolution MS of individual lipid droplets from seed tissues indicated organelle-to-organelle variation in lipid composition, suggesting that heterogeneity of lipid distributions at the cellular level may be prevalent. Here, we employed matrix-assisted laser desorption/ ionization-MS imaging (MALDI-MSI) approaches to visualize lipid species directly in seed tissues of upland cotton (Gossypium hirsutum). MS imaging of cryosections of mature cotton embryos revealed a distinct, heterogeneous distribution of molecular species of triacylglycerols and phosphatidylcholines, the major storage and membrane lipid classes in cotton embryos. Other lipids were imaged, including phosphatidylethanolamines, phosphatidic acids, sterols, and gossypol, indicating the broad range of metabolites and applications for this chemical visualization approach. We conclude that comprehensive lipidomics images generated by MALDI-MSI report accurate, relative amounts of lipid species in plant tissues and reveal previously unseen differences in spatial distributions providing for a new level of understanding in cellular biochemistry.

Spatial Mapping and Profiling of Metabolite Distributions during Germination

“…These results suggest that the heterogeneous distribution of fatty acids dictates the fatty acyl chain-dependent differential localization of lipids. Such nonuniform distribution has been observed previously in cotton (Gossypium hirsutum; Horn et al, 2012) and Camelina spp. seeds (Horn et al, 2013); thus, this is not unique to maize but, apparently, is a more general phenomenon.…”

Two Acyltransferases Contribute Differently to Linolenic Acid Levels in Seed Oil

“…Recently, MALDI-MS imaging made it possible to study lipid spatial distributions in situ directly from tissue sections (Sturtevant et al, 2016). Previous studies utilizing MALDI-MS imaging in oilseeds of cotton, C. sativa, and Arabidopsis demonstrated that lipid molecular species are not distributed equally between different seed tissues (Horn et al, 2012Sturtevant et al, 2017). The previous study on C. sativa seeds, as well as this one, shows that there are large differences between the embryonic axis, the cotyledon, and the peripheral endosperm of the seed.…”

Matrix assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) for direct visualization of plant metabolites in situ

“…A number of years ago, the Caprioli group pioneered the development of mass spectrometry imaging for localizing molecules of interest directly on the sections of mammalian tissues [2,3]. This methodology, termed matrix assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI, also referred to as imaging mass spectrometry (IMS)), has since been expanded to visualize molecules directly in plant tissues and surfaces for the localization of lipids [4,5,6,7], proteins [8], secondary metabolites [9,10,11,12,13], and various small molecules [14,15,16,17] at unprecedented spatial and chemical resolution.…”