# Responses of Medicinal and Aromatic Plants to Engineered Nanoparticles +
## 4 Effect of Metal-Based NPs on Medicinal and Aromatic Plants
### Iron-Based NPs
#### 4.3.2 Elicitor Effect  
Treatment of cell suspension cultures of _Dracocephalum polychateum_ Bornm with 100 ppm Fe\({}_{2}\)O\({}_{3}\) NPs, static magnetic field (SMF) of 30 mT, as well as combined treatment with Fe\({}_{2}\)O\({}_{3}\) NPs and SMF pronouncedly increased intracellular content of secondary metabolites, such as RA, naringin, apigenin, thymol, carvacrol, quercetin, and rutin; secretion of these secondary metabolites from cells exposed to the double stress (SMF and NPs) to the culture media was observed as well. Moreover, the applied treatments resulted in increased TPC, TFC, anthocyanins, lignin, and MDA contents and increased activity of PPO and PAL [143]. Exposures of HRs derived from 4-week-old leaves of _Dracocephalum kotschyi_ Boiss and inoculated with _Agrobacteriumrium rhizogens_ strain ATCC15834 to 75 mg/L Fe\({}_{2}\)O\({}_{3}\) NPs for 24 h resulted in improved biomass accumulation and activities of antioxidant enzymes, enhanced TPC and TFC, and contents of some valuable secondary metabolites, such as RA and xanthomicrol, which reached 9.7- and 11.87-fold higher values than in the control [162]. Moreover, inoculation with _Agrobacteriumrium rhizogens_ of HRs derived from cotyled explants of _Hycosymus reticulatus_ L, which were elicited with 900 and 450 mg/L FeNPs using exposure time of 24 and 48 h, respectively, achieved approximately fivefold higher content of propane alkaloids, hysocyanine, and scopolamine, and considerably higher activities of antioxidant enzymes compared to control [64]. Fe\({}_{2}\)O\({}_{3}\) NPs acted as highly effective elicitor, increasing the growth and production of secondary metabolites of _Cichorium intybus_ L. in HR culture induced by _Agrobacteriumrium rhizogens_ strain 15834 [219]. Treatment of _S. rebaudiana_ cultivated in vitro with 45 \(\upmu\)g/L FeNPs resulted in beneficial impact on plant growth characteristics and production of stevioside, and rebaudioside A reached 4.2 \(\pm\) 0.058 and 4.9 \(\pm\) 0.068 mg/g (d.w.). At exposure to 135 \(\upmu\)g/L FeNPs, the levels of TPC and TFC reached 3.2 \(\pm\) 0.042 and 1.6 \(\pm\) 0.022 mg/g (d.w.), respectively, although adverse effect on growth characteristics was observed. Exposure to 90 \(\upmu\)g/L FeNPs resulted in increased activities of SOD, POD, CAT, and APX [220]. In cell suspension culture of _Hypericum perforatum_ L. elicited with 100 ppb Fe\({}_{2}\)O\({}_{3}\) NPs for 72 h, enhanced concentrations of hypericin (195.62 \(\pm\) 10.00 vs. 16.272 \(\pm\) 4.62 \(\upmu\)g/g (d.w.)) and hyperorin (11.181 \(\pm\) 0.17 vs. 2.072 \(\pm\) 0.77 \(\upmu\)g/g (d.w.)) compared to the control were observed, whereas the dry weight was comparable with control. It could be assumed that the Fe\({}_{2}\)O\({}_{3}\) NPs may induce jasmonate production, playing a role in hypericin and hyperorin production, or can be involved in signal transduction process regulating jasmonate production genes in cells [141]. Simultaneous foliar application of 0.01% MgO NPs and 0.03% Fe\({}_{2}\)O\({}_{3}\) NPs on _Hibiscus sabdariffa_ plants exhibited synergistic and beneficial impact on the activity of antioxidant enzymes and anthocyanin and flavonoids levels, and reduced H\({}_{2}\)O\({}_{2}\) concentration in plants. On the other hand, at combined application of 0.03% MgO NPs and 0.03% Fe\({}_{2}\)O\({}_{3}\), ROS production increased, and the antioxidant defense system was not able to attenuate toxic effects of produced H\({}_{2}\)O\({}_{2}\) and, therefore, the observed characteristics were comparable to those of control plants [221]. Foliar treatment of _Ocinum basililicum_ L plants grown in soil with Fe nanocomplexes Fe(His)\({}_{3}\) and Fe(Arg)\({}_{3}\) resulted in an increase of sesquiterpenes and a decrease of the content of oxygenated monoterpenes in the composition of secondary metabolites of EO, and enhanced antioxidant and antimicrobial activities of plants [222].