Lignification of ray parenchyma cells in the xylem of Pinus densiflora. Part I: Microscopic investigation by POM, UV microscopy, and TOF-SIMS

Abstract

Abstract The lignification process from sapwood (sW) to heartwood (hW) in ray parenchyma cells (Pray) of Pinus densiflora has been analyzed by means of ultraviolet (UV) microscopy, acetyl bromide (CH3COBr) lignin determination, and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The cell wall layers were localized by polarized optical microscopy (POM). POM revealed that Pray have almost no secondary wall in sW and have only the outer layer of secondary wall (S1) in the transition zone (TZ) and hW. UV microscopic observations indicated that the secondary wall of Pray, which is in contact with ray tracheids (Trray), begins to lignify in sW, while the secondary wall of Pray, which is not in contact with Trray, is partially lignified in the TZ. The secondary wall of both types of Pray is completely lignified in hW. The CH3COBr lignin content in sW is slightly lower than that in hW. In the TOF-SIMS measurements, the relative intensities of the secondary ions of guaiacyl-lignin (G-lignin) in the rays in sW are significantly lower than those in hW.