Lignans in knotwood of Norway spruce: Localisation with soft X-ray microscopy and scanning transmission electron microscopy with energy dispersive X-ray spectroscopy

Tuomas Mansikkala, Minna Patanen, Anna Kärkönen, Risto Korpinen, Andrey Pranovich, Takuji Ohigashi, Sufal Swaraj, Jani Seitsonen, Janne Ruokolainen, Marko Huttula, Pekka Saranpää, Riikka Piispanen*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

Abstract

Lignans are bioactive compounds that are especially abundant in the Norway spruce (Picea abies L. Karst.) knotwood. By combining a variety of chromatographic, spectroscopic and imaging techniques, we were able to quantify, qualify and localise the easily extractable lignans in the xylem tissue. The knotwood samples contained 15 different lignans according to the gas chromatography-mass spectrometry analysis. They comprised 16% of the knotwood dry weight and 82% of the acetone extract. The main lignans were found to be hydroxymatairesinols HMR1 and HMR2. Cryosectioned and resin-embedded ultrathin sections of the knotwood were analysed with scanning transmission X-ray microscopy (STXM). Cryosectioning was found to retain only lignan residues inside the cell lumina. In the resin-embedded samples, lignan was interpreted to be unevenly distributed inside the cell lumina, and partially confined in deposits which were either readily present in the lumina or formed when OsO4 used in staining reacted with the lignans. Furthermore, the multi-technique characterisation enabled us to obtain information on the chemical composition of the structural components of knotwood. A simple spectral analysis of the STXM data gave consistent results with the gas chromatographic methods about the relative amounts of cell wall components (lignin and polysaccharides). The STXM analysis also indicated that a torus of a bordered pit contained aromatic compounds, possibly lignin.
Original languageEnglish
Article number2997
Number of pages22
JournalMolecules
Volume25
Issue number13
DOIs
Publication statusPublished - 30 Jun 2020
MoE publication typeA1 Journal article-refereed

Keywords

  • Picea abies
  • knotwood
  • extractives
  • hydroxymatairesinol
  • lignin
  • resin-embedding
  • cryosectioning
  • STXM
  • STEM-EDS
  • osmium tetroxide

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