Lignification is an important differentiation process in plant cell walls in which lignin is deposited in the polysaccharide matrix. The regulating mechanism of lignin biosynthesis is still controversial. In this study, cryo-time-of-flight secondary ion mass spectrometry (cryo-TOF-SIMS) was used to investigate the tissue and cellular distribution of chemicals relating to the lignification process. The major targets are monolignol glucosides, coniferin (coniferyl alcohol glucoside) and syringin (sinapyl alcohol glucoside). Monolignol glucosides are the promising candidates of a lignin precursor but their actual distribution in living plants were unclear because of their water-solubility. The samples were quick-frozen and the freeze-fixed distributions of the target chemicals were visualized by cryo-TOF-SIMS analyses. Target chemicals were quantified by HPLC measurements. The lignification stage of the cells was confirmed by microscopic observations using visible, polarized, and UV light. Cryo-TOF-SIMS images were obtained for the transverse and radial surface of freeze-fixed stem of Ginkgo biloba. G. biloba is an old gymnosperm having guaiacyl lignin. Coniferin distribution visualized at the transverse and radial surfaces of freeze-fixed stem of G. biloba suggested that coniferin was stored in the vacuoles, and showed good agreement with the assimilation timing of coniferin to lignin in differentiating xylem. Consequently, it is suggested that coniferin is stored in the tracheid cells of differentiating xylem and is a lignin precursor. Syringa vulgaris is an angiosperm. The lignin structure consists of guaiacyl and syringyl units. A series of measurements using cryo-TOF-SIMS/SEM, HPLC, microscopy was conducted for the freeze-fixed stem of S. vulgaris. Syringin was detected in bark strongly and also distributed at the differentiating xylem region. As a conclusion, syringin in S. vulgaris should have several uses and one of them should be a lignin precursor.

Visualization of freeze-fixed distribution of monolignol glucosides in plants

255th National Meeting (2018)

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