MALDI and MALDI-2 mass spectrometry imaging contribute to revealing the alternations in lipid metabolism in germinating soybean seeds

Seed germination plays a pivotal role in plant growth and undergoes many intricate biochemical changes including lipid metabolism. Nevertheless, little is known about lipid changes and distributions in different structures of soybean seeds during germination. Here, we applied mass spectrometry imaging (MSI) in conjunction with MS-based lipidomics to examine the lipid alterations in the embryo and cotyledon of soybean seeds during germination. To expand the coverage of lipid detection in soybean seeds, we used the novel techniques of matrix-assisted laser desorption/ionization (MALDI) and MALDI coupled with laser-postionization (MALDI-2). The results revealed that compared to MALDI, MALDI-2 enhanced the detected numbers and intensities of lipid species in various lipid classes, except for a few classes (e.g., sphingomyelin and phosphatidylcholine). Lipidomic data showed that compared to the embryo, the cotyledon demonstrated slower but similar lipid changes during germination. These changes included the reduced levels of glycerolipids, phospholipids, and sterols, as well as the increased levels of lysophospholipids. Data from MALDI&MALDI-2 MSI supported and complemented these lipidomic findings. Our work highlights the significance of integrating lipid profiles and distributions to enhance our understanding of the metabolic pathways involved in seed germination.