# Responses of Medicinal and Aromatic Plants to Engineered Nanoparticles +
## 4 Effect of Metal-Based NPs on Medicinal and Aromatic Plants
### Zinc-Based NPs  
#### 4.4.1 Impact on Germination and Plant Growth  
ZnO nanorods with a mean aspect ratio of 7, coated in gel and mixed with the seeds of _Solanum melongena_ L. and _Capsicum annum_ L., applied at doses 50, 100, and 150 mg/L, accelerated germination, which was reflected in reduced germination time and improved mean germination rate compared to control plants; application of 100 mg/L ZnO NPs ensured maximal transplant length as well as fresh and dry weight [228]. Amelioration of the seed germination rate and seedling vigor of _Capsicum annumum_ L. was observed at treatment with ZnO NPs suspensions at 100, 200, and 500 ppm, respectively. On the other hand, application of these ZnO NPs concentrations resulted in the inhibition of radical growth and stimulated accumulation of phenolic compounds [229]. Spraying of _Capsicum chinese_ Jacq. plants during the main stages of phenological development with 1000 ZnO NPs stimulated plant height, stem diameter, and Chl content, and increased fruit yield and biomass accumulation in treated plants compared to control and treatment with ZnSO\({}_{4}\), whereas the double dose of ZnO NPs adversely affected plant growth [230]. Germination of seeds of _Abelmoschus esculentus_ (L.) [PERSON] was positively affected by treatment with ZnNPs (50-500 ppm), and in 30-day-old treated plants, an increase in Chl, protein, proline, and carbohydrate contents were observed, along with pronounced reduction of the carbohydrate content of leaves [231]. Spraying of leaves of 10-day old chickpea (_Cicer arietinum_ L. var. HC-1) seedlings, with solution containing 1.5 ppm ZnO NPs, stimulated shoot dry weight, but when a dose of 10 ppm was applied, root inhibition was observed. Positive impact of ZnO NPs on plant biomass related to reduced ROS generation caused less lipid peroxidation, which also resulted in lower activity of antioxidant enzymes, such as SOD and POD, compared to the control [232]. Phytotoxic effects of the ZnO NPs and Zn microparticles (MPs) (10-2000 mg/L) on _Fagopyrum esculent_ was reflected in biomass reduction, increased Zn bioaccumulation in plants, and higher translocation factor of Zn being observed for treatment with ZnO NPs. Moreover, reduced glutathione level and CAT estimated at application of ZnO NPs indicated oxidative stress due to ROS generation [233]. In 6-week-old callus produced from leaf explants of _S. rebuadiana_ Bertoni grown in MS medium supplemented with plant growth regulators addition of 0.1 mg/L ZnO NPs significantly enhanced fresh and dry weight of callus [117]. ZnO NPs (40 nm) positively affected growth of the _Echinacea leaf_ callus and showed beneficial impact on the anticancer activity of plant extracts, in contrast to the control treatment with ZnO MPs. Moreover, application of ZnO NPs increased flavonoid contents of _Echinacea purpurea_[234]. A dose of 2000 ppm ZnO NPs increased dry weight of _Tanactum parthenium_ (L.) Schultz [PERSON] plants from 28.09 g/day (control) to 32.54 g/day, while using 1000 ppm ZnO NPs, the EO content achieved 0.9% \(v/w\) compared to 0.56% \(v/w\) observed in the control plants; an increase in Zn absorption at application of ZnO NPs was observed as well, while Fe absorption was reduced [235]. ZnO NPs at doses 0.5-2.5 mg/L applied to hormone-free MS medium inhibited root growth of ginseng root culture, deceased the lateral root number, and decreased percentage of lateral root formation was observed at exposure to 2.5 mg/L ZnO NPs. In treated plants thinner vascular tissue or cortex area and more black points in root cap area were observed compared to control. On the other hand, exposure to ZnO NPs resulted in thicker endodermis [236]. Foliar application of ZnO NPs at doses 20, 60, and 100 ppm to _Monordica charantia_ L. plants grown in pots did not considerably affect shoot weight and anthocyanin content, but pronouncedly increased Chl\(\mu\) content, as well as contents of secondary metabolites (phenols, flavonoids, and carotenoids), along with carbohydrate and proline content in a dose-dependent manner [132].