Metabolic Noise and Distinct Subpopulations Observed by Single Cell LAESI Mass Spectrometry of Plant Cells in situ

• Published in: Frontiers in plant science Vol. 9; p. 1646
• Main Authors: Stopka, Sylwia A, Khattar, Rikkita, Agtuca, Beverly J, Anderton, Christopher R, Paša-Tolić, Ljiljana, Stacey, Gary, Vertes, Akos
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Research Foundation 15.11.2018; Frontiers Media S.A
• Subjects: BASIC BIOLOGICAL SCIENCES; ENVIRONMENTAL SCIENCES; heterogeneity; in situ; mass spectrometry; metabolic noise; plant cells; Plant Science; single cell analysis; plant cells; single cell analysis; mass spectrometry; laser ablation electrospray ionization; metabolites; heterogeneity; in situ; metabolic noise
• ISSN: 1664-462X; 1664-462X
• DOI: 10.3389/fpls.2018.01646

Phenotypic variations and stochastic expression of transcripts, proteins, and metabolites in biological tissues lead to cellular heterogeneity. As a result, distinct cellular subpopulations emerge. They are characterized by different metabolite expression levels and by associated metabolic noise distributions. To capture these biological variations unperturbed, highly sensitive analytical techniques are needed that can sample tissue embedded single cells with minimum sample preparation. Optical fiber-based laser ablation electrospray ionization mass spectrometry (f-LAESI-MS) is a promising tool for metabolic profiling of single cells under ambient conditions. Integration of this MS-based platform with fluorescence and brightfield microscopy provides the ability to target single cells of specific type and allows for the selection of rare cells, e.g., excretory idioblasts. Analysis of individual leaf blade cells ( = 103) by f-LAESI-MS revealed significant differences between the prespecified subpopulations of epidermal cells ( = 97) and excretory idioblasts ( = 6) that otherwise would have been masked by the population average. Primary metabolites, e.g., malate, aspartate, and ascorbate, as well as several glucosides were detected in higher abundance in the epidermal cells. The idioblasts contained lipids, e.g., PG(16:0/18:2), and triterpene saponins, e.g., medicoside I and azukisaponin I, and their isomers. Metabolic noise for the epidermal cells were compared to results for soybean ( ) root nodule cells ( = 60) infected by rhizobia ( ). Whereas some primary metabolites showed lower noise in the latter, both cell types exhibited higher noise for secondary metabolites. grouping of epidermal and root nodule cells, based on the abundance distributions for certain metabolites (e.g., malate), enabled the discovery of cellular subpopulations characterized by different mean abundance values, and the magnitudes of the corresponding metabolic noise. Comparison of prespecified populations from epidermal cells of the closely related ( = 20) and ( = 20) revealed significant differences, e.g., higher sugar content in the former and higher levels of ascorbate in the latter, and the presence of species-specific metabolites. These results demonstrate that the f-LAESI-MS single cell analysis platform has the potential to explore cellular heterogeneity and metabolic noise for hundreds of tissue-embedded cells.