Development of a high-coverage matrix-assisted laser desorption/ionization mass spectrometry imaging method for visualizing the spatial dynamics of functional metabolites in Salvia miltiorrhiza Bge.

Profiling the spatial distributions and dynamic changes of metabolites in plant tissue is critical to elucidate the complex metabolic regulation during plant growth, development, and responses to abiotic or biotic stresses. In this study, we developed a high-coverage MALDI-MS imaging method to visualize the spatial locations of a wide spectrum of metabolites in Salvia miltiorrhiza Bge. 1,5-Diaminonaphthalene (DAN) and 1,1'-binaphthyl-2,2'-diamine (BNDM) were optimized as MALDI matrices in positive and negative ion modes respectively, due to their low background interference and high sensitivity. Moreover, a simple organic washing protocol using acetone was shown to significantly improve the sensitivity of MALDI-MSI. Using this method, we successfully imaged the spatial locations of amino acids, phenolic acids, fatty acids, oligosaccharides, cholines, polyamines, tanshinones, and phospholipids in Salvia miltiorrhiza Bge. In addition, the distributions of some metabolites in Salvia miltiorrhiza Bge root and stem were found to exhibit good spatial match with plant tissue structure. Thus, our method provides a spatially-resolved way to map the plant metabolic networks and to understand the physiological roles of several plant metabolites.