ToF-SIMS imaging reveals that p-hydroxybenzoate groups specifically decorate the lignin of fibres in the xylem of poplar and willow

  • 1 Department of Biochemistry, Chemistry and Physics, Niagara University, 5795 Lewiston Road, Lewiston, USA
  • 2 Department of Wood Science, University of British Columbia, 2424 Main Mall, Vancouver, Canada
Robyn E. GoacherORCID iD: https://orcid.org/0000-0001-7863-4888, Yaseen MottiarORCID iD: https://orcid.org/0000-0002-4106-6159 and Shawn D. MansfieldORCID iD: https://orcid.org/0000-0002-0175-554X

Abstract

Esterified phenolics occur as γ-linked lignin acylations in many plant taxa but little is known about the distribution or function of such groups. In the family Salicaceae, p-hydroxybenzoate groups are present in the lignin of poplars (Populus spp.) and willows (Salix spp.). In this study, the distribution of cell wall-bound p-hydroxybenzoate was examined in different tissue and cell types of poplar and willow trees. This analysis showed that p-hydroxybenzoate groups were most prevalent in juvenile stems, and were elevated in tension wood and following nitrogen fertilisation. Closer examination of stem cross-sections using time-of-flight secondary-ion mass spectrometry (ToF-SIMS) directly showed that p-hydroxybenzoate groups occur predominantly in the cell walls of fibres and are largely absent from vessel elements. These results point to a role for ester-linked groups in modifying the syringyl-rich lignin of fibres, perhaps to strengthen the cell walls of these structural elements or to increase lignification rates.

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