TITLE:
Immunolocalization of a Normal Wood Specific Pectin Methylesterase (CoPME) and Quantification of PME Gene Expression in Differentiating Xylem of Chamaecyparis obtusa
AUTHORS:
Akinori Ota, Masato Yoshida, Saori Sato, Hideto Hiraide, Miyuki Matsuo-Ueda, Hiroyuki Yamamoto
KEYWORDS:
Reaction Wood, Wood Formation, Cell Differentiation, Immunohistochemistry, Quantitative Polymerase Chain Reaction, Monoclonal Antibody
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.10 No.11,
November
6,
2019
ABSTRACT: The transverse section of compression wood tracheids
has a circular shape and intercellular spaces. The cause has not been
determined yet; however, we hypothesized that peeling of the cell wall adhesion
would cause cellular intervals, resulting in circularity of the transverse
section of tracheids. Homogalacturonan, a type of pectin, functions in cell
wall adhesion. Further, pectin methylesterase (PME) is involved in
functionalization of homogalacturonan. We quantitated PME gene expression
levels in differentiating xylem cells using different degrees of compression
wood samples and examined the correlation with circularity of the transverse
section of tracheids in each sample. We found that lower gene expression level
of the sample corresponded with increasing circularity of the transverse
section of tracheids. It is considered that the transverse section of
compression wood tracheids becomes circular by suppression of PME gene
expression during differentiation. Further, we observed the normal wood specific
pectin methylesterase (CoPME) localization in differentiating xylem tracheids
by immunolabeling. Labels localized at the entire perimeter of the compound
middle lamella in normal wood, whereas sparse labeling was found in compression
wood. It suggests that cell walls adhere at sites of CoPME function in
differentiating xylem tracheids, but there is inadequate adhesion between cell
walls where CoPME does not function. At the end of the expansion zone, the
volume of the cell decreases due to a decrease in the turgor pressure of the tracheid.
Further, due to moisture shrinkage of the tracheid, the adhesion begins to peel
off in places of inadequate adhesion between cell walls, resulting in cell gaps
and, thereby, generating a circular cell shape of cell wall formation in
compression wood.