Single-Cell Metabolite Profiling of Stalk and Glandular Cells of Intact Trichomes with Internal Electrode Capillary Pressure Probe Electrospray Ionization Mass Spectrometry

In
this report, we developed the pressure probe electrospray ionization-mass
spectrometry with internal electrode capillary (IEC-PPESI-MS) which
enables high spatial-resolution cell sampling, precise postsampling
manipulation, and high detection sensitivity. Using this technique,
a comparative in situ single-cell metabolite profiling
of stalk and glandular cells, the two adjacent cell types comprising
a trichome unit in tomato plants (Solanum lycopersicum L.), were performed to clarify the extent of metabolic differentiation
between two cell types as well as among different types of trichomes.
Owing to high sensitivity of the system, less than a picoliter cell
sap from a single stalk cell sufficiently yielded a number of peaks
of amino acids, organic acids, carbohydrates, and flavonoids. The
minimal cell sap removal from a stalk cell without severe disturbance
of trichome structure enabled sequential analysis of adjacent glandular
cell on the same trichome, which showed the presence of striking differences
in metabolite compositions between two adjacent cell types. Comparison
among different types of trichome also revealed significant variations
in metabolite profiles, particularly in flavonoids and acyl sugars
compositions. Some metabolites were found only in specific cell types
or particular trichome types. Although extensive metabolomics analysis
of glandular cells of tomato trichomes has been previously documented,
this is the first report describing cell-to-cell variations in metabolite
compositions of stalk and glandular cells as well as in different
trichome types. Further application of this technique may provide
new insights into distinct metabolism in plant cells displaying variations
in shape, size, function and physicochemical properties.