Distribution of metabolites in germinating sorghum seeds. Cross sections of germinating sorghum seed were analyzed by timsTOF fleX MALDI-2 in positive ion mode at 10 µm lateral resolution to obtain images of molecular distributions across the samples. All images A–H are displayed with scale bars for size. A, Fluorescence image of cross section for reference. B, [C₄₄H₈₄NO₈P+K]⁺, sum formula corresponding to a putative phospholipid, 1,2-dioleoyl-sn-glycero-3-phosphocholine, or 1-linoleoyl-2-stearoyl-sn-glycero-3-phosphocholine. C–E, Dhurrin and two derivatives previously demonstrated to accumulate in scutellum and/or embryonic axis (radicle + coleoptile) (Montini et al., 2020). C, Dhurrin, detected as [M+K]⁺, only in the embryonic axis. D, Dhurrin acid, detected as [M+Na]⁺, in scutellum and embryonic axis. E, Glutathione derivative of dhurrin, GS-p-hydroxyphenylacetic acid, detected as [M+Na]⁺, in scutellum and embryonic axis. F–H, Phenolic compounds potentially containing caffeic acid moieties, accumulated in scutellum and other tissues. Sum formulae deduced from m/z values, but absolute structures not confirmed. F, [C₂₅H₂₄O₁₂+H]⁺, sum formula corresponding to 3,4-dicaffeoylquinic acid, apparently more highly accumulated in scutellum than in embryonic axis. G, [C₁₈H₁₆O₈+Na]⁺, sum formula corresponding to rosmarinic acid, but most likely an isomer as this compound is not known to accumulate in Poaceae. Detected in all living tissues. H, [C₁₇H₁₄O₇+H]⁺. Dhurrin and dhurrin acid can be found conjugated with caffeic acid in sorghum. This deduced sum formula corresponds to a hypothetical caffeic acid conjugated p-hydroxymandelic acid (dhurrin acid aglycone), but may more likely be a flavanone or flavone such as dimethylquercetin. Detected in scutellum and embryonic axis. All MS images: For increased clarity, low- and high-end intensity thresholds have been adjusted. The corresponding color-coded scale bars are displayed under each mass spectrometry image.