Subcellular-level resolution MALDI-MS imaging of maize leaf metabolites by MALDI-linear ion trap-Orbitrap mass spectrometer
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A significant limiting factor in achieving high spatial resolution for matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS) imaging is the size of the laser spot at the sample surface. Here, we present modifications to the beam-delivery optics of a commercial MALDI-linear ion trap-Orbitrap instrument, incorporating an external Nd:YAG laser, beam-shaping optics, and an aspheric focusing lens, to reduce the minimum laser spot size from ~50 μm for the commercial configuration down to ~9 μm for the modified configuration. This improved system was applied for MALDI-MS imaging of cross sections of juvenile maize leaves at 5-μm spatial resolution using an oversampling method. A variety of different metabolites including amino acids, glycerolipids, and defense-related compounds were imaged at a spatial resolution well below the size of a single cell. Such images provide unprecedented insights into the metabolism associated with the different tissue types of the maize leaf, which is known to asymmetrically distribute the reactions of C4 photosynthesis among the mesophyll and bundle sheath cell types. The metabolite ion images correlate with the optical images that reveal the structures of the different tissues, and previously known and newly revealed asymmetric metabolic features are observed.
KeywordsMass spectrometry imaging Metabolite Maize
This work was supported by the US Department of Energy (DOE), Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. MDY-N acknowledges the support of the National Science Foundation under Award No. EEC-0813570 and Award No. IOS-1354799, which co-sponsored the development of the genetic stocks imaged in this study. The Ames Laboratory is operated by Iowa State University under DOE Contract DE-AC02-07CH11358.
- 4.Chen Y, Allegood J, Liu Y, Wang E, Cachon-Gonzalez B, Cox TM, Merrill AH Jr, Sullards MC (2008) Imaging MALDI mass spectrometry using an oscillating capillary nebulizer matrix coating system and its application to analysis of lipids in brain from a mouse model of Tay-Sachs/Sandhoff disease. Anal Chem 80(8):2780–2788. doi: 10.1021/ac702350g CrossRefGoogle Scholar
- 10.Hoelscher D, Shroff R, Knop K, Gottschaldt M, Crecelius A, Schneider B, Heckel DG, Schubert US, Svatos A (2009) Matrix-free UV-laser desorption/ionization (LDI) mass spectrometric imaging at the single-cell level: distribution of secondary metabolites of Arabidopsis thaliana and Hypericum species. Plant J 60(5):907–918. doi: 10.1111/j.1365-313X.2009.04012.x CrossRefGoogle Scholar
- 13.Kettling H, Vens-Cappell S, Soltwisch J, Pirkl A, Haier J, Muething J, Dreisewerd K (2014) MALDI mass spectrometry imaging of bioactive lipids in mouse brain with a Synapt G2-S mass spectrometer operated at elevated pressure: improving the analytical sensitivity and the lateral resolution to ten micrometers. Anal Chem 86(15):7798–7805. doi: 10.1021/ac5017248 CrossRefGoogle Scholar
- 20.Korte A, Yagnik G, Feenstra A, Lee Y (2015) Multiplex MALDI-MS imaging of plant metabolites using a hybrid MS system. In: He L (ed) Mass spectrometry imaging of small molecules, vol 1203, Methods in Molecular Biology. Springer, New York, pp 49–62. doi: 10.1007/978-1-4939-1357-2_6 CrossRefGoogle Scholar
- 26.Vermerris W, Nicholson R (2006) Phenolic compound biochemistry. Springer, DordrechtGoogle Scholar
- 36.Meihls LN, Handrick V, Glauser G, Barbier H, Kaur H, Haribal MM, Lipka AE, Gershenzon J, Buckler ES, Erb M, Koellner TG, Jander G (2013) Natural variation in maize aphid resistance is associated with 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one glucoside methyltransferase activity. Plant Cell 25(6):2341–2355. doi: 10.1105/tpc.113.112409 CrossRefGoogle Scholar
- 37.Sicker D, Frey M, Schulz M, Gierl A (2000) Role of natural benzoxazinones in the survival strategy of plants. In: Kwang WJ (ed) International review of cytology, vol 198. Academic Press, p 319–346. doi: 10.1016/S0074-7696(00)98008-2