POORLY AND NON-LIGNIFIED REGIONS IN THE MIDDLE LAMELLA CELL CORNERS OF BIRCH (BETULA-VERRUCOSA) AND OTHER WOOD SPECIES

Middle lamella cell corners in birch wood frequency show a non-homogeneous structure and the existence of less dense (i.e. electron-lucent) regions. Using a variety of cytochemical, immunological and mercurisation techniques in conjunction with electron microscopy, the distribution of lignin within these regions was studied. Results showed the regions to have a variable lignin content consistent with intermediate and incomplete stages of lignification. Observations on corner regions partially degraded by decay fungi further showed the electron-lucent regions to possess an elevated level of non-lignified components (presumably carbohydrates) with a fibrillar type structure. Examination of a range of other wood species (including hard- and softwoods) by TEM showed similar structural variations in middle lamella cell corner homogeneity suggesting a common feature. It is considered that this natural variation in cell corner density and lignification may lead to errors when lignin concentrations of cell corners are used in ratio estimates of lignin in secondary cell wall layers.