Fig. 2

Comparative AP-SMALDI mass spectrometry imaging of stem base sections obtained from FRR-infected and non-infected wheat seedlings. a–c RGB overlay of m/z images showing the spatio-temporal distribution of two constitutive wheat metabolites and two pathogen-derived metabolites. In both treatments the putative compound delphinidin sophoroside, [M + H]⁺, m/z 627.1532 (blue) was found to be located in stem and leaf sheath tissues at 10 and 14 days after root inoculation (dai) with F. graminearum, but was found absent from the stem at 21 dai (a, b). The triterpenoid quinquenoside, [M + Na]⁺, m/z 819.5117 (green) was found to be enriched in the vascular tissues of stem and leaf sheath at 10 and 14 dai, but was found more widespread distributed at 21 dai (a–c). In infected stem bases the fungal glycosphingolipid cerebroside C, [M + K]⁺, m/z 792.5391 (red) was detected in specific areas of the abaxial epidermis of leaf sheath at 10 dai (a). At 14 dai the mycotoxin enniatin B, [M + Na]^+, m/z 662.3987 (red) was found to be present in the entire abaxial epidermis of leaf sheath and at 21 dai additionally in the cortical parenchyma (b, c). All AP-SMALDI-MS images were obtained at 15 μm step size. Scale bars: 500 µm. d–f Optical images of F. graminearum-infected and non-infected stem base. Cross sections show leaf sheath (Ls) and stem tissues, each comprising epidermal layers (Ep) and vascular bundles (Vb) that are surrounded by cortex parenchyma,—as exemplary signified in d. Scale bars: 500 µm