Genotype- and age-dependent patterns of lignin and cellulose in regenerants derived from 80-year-old trees of black mulberry (<Emphasis Type="Italic">Morus nigra</Emphasis> L.)

Proliferating shoot cultures of black mulberry (Morus nigra), derived from axillary buds of two donor trees designated as Mn1 and Mn2, more than 80 years of age, were established in vitro. Subsequently, shoot-tips were used to induce both axillary and adventitious shoot regeneration following incubation on Murashige and Skoog medium containing 14 different treatments of various concentrations of plant growth regulators, including 6-benzyladenine (BA), thidiazuron (TDZ), and combinations of BA with indole-3-butyric acid (IBA) and TDZ with BA. The highest shoot proliferation of 5.3 shoots per explant for the Mn1 tree and 6.9 shoots per explant for the Mn2 tree were obtained when explants were incubated on a medium containing 0.5 mg l⁻¹ BA and 0.1 mg l⁻¹ IBA. The maximum frequency of adventitious rooting was similar for both genotypes. Changes in lignin and cellulose content, macromolecular properties of dioxane and Klason lignins, lignin monomer composition, and macromolecular properties of cellulose were determined in 1-year-old and 3 year-old micropropagated plants, as well as in the donor trees. Lignin and cellulose properties were significantly dependent on the genotype, the age and the mutual interaction of both these factors. The syringyl to guaiacyl weight ratio in lignin rose with the age of the micropropagated plants. Moreover, the tensile strength of wood in 1-year-old plants was supported by a high cellulose degree of polymerization. The highest polydispersity index of cellulose was detected in 3-year-old plants.