Recently, Professor Pan Yang's team from the National Synchrotron Radiation Laboratory of the University of Science and Technology of China used the self-developed desorption electrospray ionization/secondary photoionization (DESI/PI) mass spectrometry imaging platform (Analytical Chemistry, 2019, 91, 6616-6623) combined with porous PTFE blotting technology to achieve spatial imaging of metabolites in a variety of plant leaves. The research results were published in the international journal "Analytical" in the form of frontcover with the title of "Enhanced Coverage and Sensitivity of ImprintDESI Mass Spectrometry Imagingfor Plant Leaf Metabolites by Post-Photoionization". Chemistry (doi.org/10.1021/acs.analchem.2c03329).
The chemical structures of about 200,000 plant metabolites have been identified in known plant populations. Compositional analysis and spatial imaging of plant metabolites are of great significance for exploring the biosynthesis, transport, physiological mechanism, self-regulation mechanism and interaction between plant and ecology. Mass spectrometry imaging is a molecular imaging technique that has emerged in recent years, which has the advantages of no fluorescent labeling and no need for complex sample preparation. However, due to the presence of plant cuticle and epidermal wax, it is difficult for conventional soft ionization techniques such as MALDI and DESI to penetrate the cuticle and act on mesophyll tissue, thus making it impossible to directly image metabolites in plant leaves.
Figure 1.Cover of the journal
Figure 2.Flow chart of blot DESI/PI mass spectrometry imaging
The research group transferred the plant metabolites in the leaves to the porous PTFE materials by blotting method, and imaged the imprinted materials, which could realize the indirect imaging of plant metabolites in the leaves. Due to the use of DESI/PI technology, compared with the traditional DESI method, up to 100 secondary metabolites such as terpenoids, flavonoids, amino acids and glycosides can be newly detected in the positive ion mode. The overall metabolite signal intensity can be enhanced by an order of magnitude in negative ion mode.
Figure 3.Ginkgo biloba leaf imprint mass spectrometry imaging
The research group further used this technology to study tea, and found that caffeine was enriched in the leaf midrib, and theanine was enriched in the petiole and extended to the midrib and leaf tail, which provided strong evidence for the biosynthesis site and transport path of caffeine mainly in the midrib of tea and the synthesis of theanine in the root of tea and transport to the leaf. The important flavonoid metabolites in the biosynthesis network of catechins (EC/C, EGC/GC, ECG/CG, EGCG/GCG) in tea were also detected and spatially distributed in the form of mass spectrometry imaging, indicating that imprinted DESI/PI imaging technology has great potential in exploring plant metabolic transformation sites and pathways.
Figure 4.Tea blot imaging and catechin biosynthesis network