A Depth-Controlled Longitudinal Cutting Strategy Enhances MALDI-MSI of Entire Leaves

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) enables spatial analysis of endogenous metabolites in plant leaves, contributing to insights into the complex chemical, spatial, and temporal variations in plant metabolism. Longitudinal sectioning can offer rich information about tissue heterogeneity and molecular distribution within flat leaf tissues but is much more challenging. In this study, we developed a depth-controlled longitudinal cutting (DCLC) strategy for leaf processing. An in-house device was used to achieve longitudinal cutting of various leaves, which has an adjustable cutting range of up to 3 cm. Longitudinal sections as thin as 5 μm can be prepared, and a thickness of 30 μm was chosen in this work to balance the tissue integrity and MALDI-MSI performance. For leaves with a pronounced cuticle, DCLC facilitates exposure of internal tissues and reduces cuticle-related ion suppression in MALDI-MSI. By changing the blade-base gap and repeating the cutting procedure, multiple longitudinal sections can be obtained from a single leaf, allowing the "middle" part to be further resolved into multiple consecutive planes in future applications.