Direct Depolymerization Coupled to Liquid Extraction Surface Analysis-High-Resolution Mass Spectrometry for the Characterization of the Surface of Plant Tissues

Direct surface analysis mass spectrometry uncovers the vertical distribution of cuticle-associated metabolites in plants

The plant cuticle covers the plant's entire aerial surface and acts as the outermost protective layer. Despite being crucial for the survival of plants, surprisingly little is known about its biosynthesis. Conventional analytical techniques are limited to the isolation and depolymerization of the polyester cutin, which forms the cuticular scaffold. Although this approach allows the elucidation of incorporated cutin monomers, it neglects unincorporated metabolites participating in cutin polymerization. The feasibility of a novel approach is tested for in situ analysis of unpolymerized cuticular metabolites to enhance the understanding of cuticle biology. Intact cotyledons of Brassica napus and Arabidopsis thaliana seedlings are immersed in organic solvents for 60 seconds. Extracts are analyzed using high-resolution direct infusion mass spectrometry. A variety of different diffusion routes of plant metabolites across the cuticle are discussed. The results reveal different feasibilities depending on the research question and cuticle permeabilities in combination with the analyte's polarity. Especially hydrophilic analytes are expected to be co-located in the cell wall beneath the cuticle causing systematic interferences when comparing plants with different cuticle permeabilities. These interferences limit data interpretation to qualitative rather than quantitative comparison. In contrast, quantitative data evaluation is facilitated when analyzing cuticle-specific metabolites or plants with similar cuticle permeabilities.

Sculpting the surface: Structural patterning of plant epidermis

Plant epidermis are multifunctional surfaces that directly affect how plants interact with animals or microorganisms and influence their ability to harvest or protect from abiotic factors. To do this, plants rely on minuscule structures that confer remarkable properties to their outer layer. These microscopic features emerge from the hierarchical organization of epidermal cells with various shapes and dimensions combined with different elaborations of the cuticle, a protective film that covers plant surfaces. Understanding the properties and functions of those tridimensional elements as well as disentangling the mechanisms that control their formation and spatial distribution warrant a multidisciplinary approach. Here we show how interdisciplinary efforts of coupling modern tools of experimental biology, physics, and chemistry with advanced computational modeling and state-of-the art microscopy are yielding broad new insights into the seemingly arcane patterning processes that sculpt the outer layer of plants.

Induced Self-aspiration Electrospray Ionization Mass Spectrometry for Flexible Sampling and Analysis

Electrospray ionization (ESI) operating in pulse mode can enhance the utilization efficiency of the electrospray ions by a mass spectrometer. Herein, a novel ionization technique called induced self-aspiration-electrospray ionization (ISA-ESI) was developed based on self-aspiration sampling and capacitive induction. The sample solution polarized in a strong electric field was pulsed drawn into a capillary that was connected to a subambient chamber. The sample solution with polarized ions forms a charged liquid column, which can initiate an electrospray when reaching the capillary outlet. In addition to the self-aspiration ability, the use of a constant high voltage supply and no electrical contact with the solution can also simplify the sampling and ionization operation, enabling a convenient ESI mass spectrometry analysis. The developed ISA-ESI source has been used for multidimensional monitoring of chemical reactions as well as liquid extraction surface analysis of plant tissues. It was expected that this special ionization method could be extended to automated high-throughput ESI-MS analysis.