Elicitation and Enhancement of Phenolics Synthesis with Zinc Oxide Nanoparticles and LED Light in Lilium candidum L. Cultures In Vitro

Abstract

In this study, we identified and determined the content of phenolic compounds in Lilium candidum adventitious bulbs formed in vitro. HPLC analysis revealed the presence of four phenolic acids: chlorogenic, caffeic, p-coumaric, and ferulic acid. Phenolic acid content was assessed in adventitious bulbs formed in vitro on media supplemented with zinc oxide nanoparticles (ZnO NPs at 25, 50, and 75 mg/L) under fluorescent light (FL) or in darkness (D). The second experiment analyzed the effects of light-emitting diodes (LEDs) of variable light spectra on the formation of adventitious bulbs and their contents of phenolic acids. Spectral compositions of red (R; 100%), blue (B; 100%), red and blue (RB; 70% and 30%, respectively), a mix of RB and green (RBG) in equal proportions (50%), and white light (WLED, 33.3% warm, neutral, and cool light, proportionately) were used in the study. FL and D conditions were used as controls for light spectra. Bulbs grown in soil served as control samples. The most abundant phenolic acid was p-coumaric acid. Treatment with LED light spectra, i.e., RB, RBG, WLED, and B, translated into the highest p-coumaric acid concentration as compared with other treatments. Moreover, all the bulbs formed in light, including those grown on the media supplemented with ZnO NPs and under FL light, contained more p-coumaric acid than the bulbscales of the control bulbs grown in soil. On the other hand, control bulbs grown in soil accumulated about two to three times higher amounts of chlorogenic acid than those formed in vitro. We also found that the levels of all examined phenolics decreased under FL, R, and D conditions, while the bulblets formed in vitro under RB light showed the highest phenolic content. The use of ZnO NPs increased the content of p-coumaric, chlorogenic, and caffeic acid in the bulblets formed under FL as compared with those grown in darkness.