Plants are considered prospective sources of a wide range of pharmaceutical substances. Plant biomass can be applied to the secretion of desired secondary metabolites with biological activity. In nature, the amount of bioactive compounds received from plants is relatively low, and their extraction is problematic. To overcome all of these problems and increase biomass proliferation, as well the production of secondary metabolites, in vitro techniques could be applied. Furthermore, elicitation is a well-known method to stimulate the secretion of bioactive substances. Studies show that immobilization could also be beneficial for increasing plant growth and productivity. Elicitor-coated polymeric-based scaffolds are a combination of both of these methods. Such platforms could be used as easy and cheap bioengineering tools for increasing the production of secondary metabolites.

The scope of this study was to examinate the influence of the fungal chitosan's viscosity on the biomass growth and the secondary metabolite production in Rindera graeca hairy root cultures. The transgenic roots were immobilized on hybrid PLA–chitosan scaffolds. The surfaces of the scaffolds were modified using different chitosan viscosities, i.e., 10-120 cps, 100-300 cps, or 2000-3500 cps. The average concentration of elicitors in the platforms was 25% m/m. As a control culture, transgenic roots cultured on unmodified PLA scaffolds have been applied. The increase in the fresh biomass and the amount of naphthoquinones produced in the Rindera graeca hairy root cultures were determined quantitatively.

Increasing the viscosity of the fungal chitosan had a great impact on the plant biomass proliferation, as well as on the secretion of secondary metabolites. Increasing growth of the hairy roots was observed with increasing chitosan viscosity, while the effect on the production of the naphthoquinone derivatives was quite the opposite.

This research was funded by the National Science Centre (NCN), Poland, grant no. 2021/41/N/ST8/00958.