Distribution and roles of chemical components in the phellem cell walls of Cerasus jamasakura (Siebold ex Koidz.) H. Ohba

Abstract

Abstract Bark, the outermost tissue covering the stem, plays an important role in protecting trees from damage induced by living organisms and the surrounding environment. Bark differs from the xylem mainly by the presence of suberin in phellem cell walls. However, to date few studies have examined the role of suberin and its interactions with other chemical components in the phellem. Consequently, this study aimed to understand the distribution of chemical components, including suberin and lignin, and their respective roles in phellem cell walls, using Cerasus jamasakura (Siebold ex Koidz.) H. Ohba. Suberin and lignin were selectively removed from thin strip specimens that were intermittently collected from the branches of a living tree. Fourier transform infrared (FTIR) spectroscopy suggested that desuberinization sufficiently removed both suberin and other matrix substances within a few minutes of treatment, whereas delignification exclusively removed lignin. Further microscopic observation revealed that the most suberin present was distributed in the secondary wall of phellem cells, whereas lignin was present in both the tertiary wall and compound middle lamella. In addition, the cell wall collapse of the phellem was only found in desuberinized specimens, whereas delignified specimens only showed monotonic contraction. Taken together, these results suggest that the presence of suberin in the phellem contributes to the shape stability of phellem cell walls.