# Responses of Medicinal and Aromatic Plants to Engineered Nanoparticles +
## 4 Effect of Metal-Based NPs on Medicinal and Aromatic Plants
### Iron-Based NPs  
#### 4.3.1 Impact on Plant Growth and Assimilation Pigments  
Chitosan-coated Fe\({}_{3}\)O\({}_{4}\) NPs with sizes 3-22 nm applied at doses 200 and 400 mg/kg showed beneficial impacts on seed germination and growth of _Capsicum annuum_ L. seedlings, whereby their efficiency was better than that of bare Fe\({}_{3}\)O\({}_{4}\) NPs [214]. Priming of roots of 28-day-old chilli and marigold plants for 3 h in the suspension of FeS\({}_{2}\) NPs (100 ug/mL) prior to transplantation had beneficial impact on chilli yields and mean flower number of marigold, which was approximately doubled as compared to control (27 vs. 13) [215]. Introduction of 0.3 mg/L FeNPs (27.0 \(\pm\) 0.51 nm) instead of FeSO\({}_{4}\) into a MS nutrient medium increased root length, root activity (evaluated as the reduction of triphenyltetrazolzolium), and leaf Chl in _Capsicum annuum_ plants by 118, 58 and 5% related to control. A 10-fold higher FeNPs concentration increased Chl content even by 27% and beneficial impact on the above-mentioned characteristics were observed also at a combination of FeNPs with CuNPs or ZnNPs. It could be mentioned that the applied FeNPs concentration of 0.3 mg/L was 18.7-fold lower than that contained in standard MS medium [216].  
Treatment with Fe\({}_{2}\)O\({}_{3}\) NPs and a chelated Fe-EDTA fertilizer increased Fe content of _Arachis hypogaea_ plants cultivated in pots compared to control; Fe\({}_{2}\)O\({}_{3}\) NPs increased root length, plant height, and biomass of peanut plants. The Fe\({}_{2}\)O\({}_{3}\) NPs promoted the plant growth via regulating contents of phytohormones and antioxidant enzyme activities. Adsorption of Fe\({}_{2}\)O\({}_{3}\) NPs onto sandy soil improved availability of Fe to the plants suggesting that Fe\({}_{2}\)O\({}_{3}\) NPs can be used as fertilizer instead of traditional Fe fertilizers [91]. _Zingiber officinal_ Rosc. plants cultivated hydroponically in Hoagland solution containing 100 ppm Fe\({}_{2}\)O\({}_{3}\) NPs exhibited higher protein levels (1.699 \(\upmu\)g/mL) compared to plants treated with Fe-EDTA (1.108 \(\upmu\)g/mL) and plants cultivated without Fe\({}^{3+}\) addition to nutrient solution (0.208 \(\upmu\)g/mL). Similarly, in plants exposed to Fe\({}_{2}\)O\({}_{3}\) NPs, the total Chl and carotenoid content was 1.18- and 1.28-fold higher than in plants treated with Fe-EDTA, and 2.23- and 2.25-fold higher than in control plants. Fe content in rhizome of Fe\({}_{2}\)O\({}_{3}\) NPs-treated plants increased as well, suggesting that these NPs can be used to mitigate chlorosis [217].  
Comparison of yield, growth, and Fe uptake of _Cuminumuminum_ L. plants grown on the calcareous soils and sprayed twice during the season, before and after flowering (with a 10 day interval), using three various Fe-containing fertilizers, showed that the highest weight of 1000 grains and plant growth was observed at application of Fe-nano-chelate using a dose 1 g/L, while treatment with Fe-siderophore was found to be the most suitable for seed fortification with Fe [218].