Microwave Radiation as an Inducer of Secondary Metabolite Production in Drosera rotundifolia In Vitro Plantlets

In this study, low-intensity microwave irradiation (frequency of 2.45 GHz; 26.3 kW m^-3 power density) for 0, 5, and 30 s was tested for the first time on Drosera rotundifolia in vitro plantlets to explore its effect on the production of highly valued phenolic compounds. Analysis of the extracts obtained from irradiated plantlets revealed time-dependent increases in the levels of photosynthetic pigments, particularly the carotenoids, whereas symptoms of growth decline were not observed. Similarly, the highest total antioxidant capacity and total phenolic and flavonoid contents were detected in 30-s-irradiated plantlets. High-performance liquid chromatography analysis revealed that the content of the bioactive phenolics 5-hydroxy-7-methylnaphthalene-1,4-dione (1), 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxychromen-4-one (2), and 2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-3-[(3R,4S,5R,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxychromen-4-one (3), which are considered to be responsible for the pharmacological properties of this species, was around twofold higher in 30-s-irradiated plantlets than in controls. Nevertheless, the accumulation of 5-hydroxy-2-methylnaphthalene-1,4-dione (4), which was present only in trace amounts in the plant roots, decreased by 30% upon microwave irradiation. The results indicate that microwave treatment acts as an effective inducer of the production of phenylpropanoid compounds, which opens up new opportunities for its use in biotechnological applications.