Variability in growth and biosynthetic activity of Calendula officinalis hairy roots

Calendula officinalis is a widespread medicinal plant with a sufficiently well-studied chemical composition. Secondary metabolites synthesized by C.officinalis plants have pharmacological value for treating numerous diseases, and various types of aseptic in vitro cultures can be used as a source of these compounds. From this perspective, hairy roots attract considerable attention for the production of bioactive chemicals, including flavonoids with antioxidant activity. This paper shows the possibility of C.officinalis hairy roots obtaining with 100% frequency by Agrobacterium rhizogenes genetic transformation. Hairy root lines differed in growth rate and flavonoid content. In particular, flavonoids were accumulated in the amount of up to 6.68 ± 0.28 mg/g of wet weight. Methyl jasmonate in the concentration of 10 µM inhibited root growth to a small extent but stimulated the synthesis of flavonoids. The antioxidant activity and the reducing power increased in the roots grown in the medium with methyl jasmonate. The strong correlation of antioxidant activity and reducing power with flavonoid content was detected. The influence of extraction conditions on the content of flavonoids in the extracts and their bioactivity was determined. The potent reducing activity of extracts from hairy roots allowed the production of silver nanoparticles, which was confirmed by transmission electron microscopy.