Physical-chemical properties of Betula pendula Roth trunk tissue cell walls

The physical-chemical parameters of the cell walls in the trunk conducting tissues (polymer matrix swelling index, ion exchange capacity, ionization constant of active groups) were studied during active growth in two forms of silver birch differing in wood texture - common silver birch (Betula pendula var. pendula) and Karelian birch (B. pendula var. carelica). By determining these parameters, we assessed the rigidity of studied cell walls, the qualitative and quantitative composition of active groups in the ion exchange processes, i.e. the structural and functional dimensions of the cell wall. The cell wall swelling index in Karelian birch was much lower both in phloem and in xylem tissues. The reasons behind the lower swelling of the cell walls in Karelian birch differed depending on the types of tissue. We assumed that the rigidity of the cell wall structure in xylem tissues was higher in B. pendula var. carelica in comparison with B. pendula var. pendula. Higher rigidity of the xylem structure is due to an increased proportion of phenolic compounds, both within lignin and in the form of diferulic cross-bridges. The reason for lower cell wall swelling in the phloem tissues of Karelian birch was the lower number of functional groups in the apoplast, which was in turn conditioned by carboxyl groups of hydroxycinnamic acids and phenolic -OH groups. The distinctions between Karelian birch and common silver birch in the composition and properties of trunk tissue cell walls are assumed to be related to the conditions under which cell wall components are synthesized. The high content of carbohydrates recorded in Karelian birch trunk tissues in the period preceding intensive growth may be a factor promoting rapid development of the secondary wall, its greater lignification, and structural rigidity.