Advances in cellular and sub-cellular level localization of lipids and metabolites using two- and three dimensional high-spatial resolution MALDI mass spectrometry imaging

This thesis presents efforts in the advancement and application of high-spatial resolution matrix-assisted laser desorption ionization-mass spectrometry imaging (MALDI-MSI) for the mapping of small metabolites and lipids at the cellular and sub-cellular level. The following work presents a number of advances, using both 2and 3-dimensional MALDI-MSI to enable visualization at the sub-cellular level. The first chapter consists of a general introduction to the technique of MALDI-MSI, and the seventh and final chapter provides a brief summary of the presented work and possible future directions. The second chapter presents a technology development for the optimization and application of matrix recrystallization to improve lipid ion signals in maize embryos and leaves. Using the optimized recrystallization conditions, the ion signals were improved three times, enhancing the image quality of lipid species with no apparent changes in their localization. Additionally, when methanol was used as a recrystallization solvent, unexpected side reactions were observed between phosphatidic acid and methanol vapor, suggesting recrystallization solvent should be carefully selected to avoid side reactions. The third chapter presents an application using 5and 10-m high spatial resolution MALDI-MSI to explore quantitative fatty acyl distributions of two classes of thylakoid membrane lipids along the developmental gradient of maize leaves in two inbred lines, B73 and Mo17, and the reciprocal hybrid lines, B73xMo17 and Mo17xB73. This study demonstrated that high-resolution MALDI-MSI analysis can be directly applied to multicellular plant tissues to uncover cell-specific metabolic biology that has not been possible using traditional metabolomics methodologies. For example, certain thylakoid membrane lipids (e.g. phosphatidylglycerol (PG) 32:0) show genotype-specific differences in cellular distributions.