# Responses of Medicinal and Aromatic Plants to Engineered Nanoparticles +
## 4 Effect of Metal-Based NPs on Medicinal and Aromatic Plants
### TiO\({}_{2}\)-Based NPs
#### 4.5.1 Impact on Germination, Plant Growth and Assimilation Pigments  
TiO\({}_{2}\) NPs (10-25 nm) applied at doses 20-40 mg/L were found to accelerate the germination characteristics of _Alyssum homolocarpum_, _Carum copictum_, and _Nigella sativa seeds_, and increase their vigor, while most effective stimulation of germination of _Salvia mirazyanti_ seeds was obtained with 80 mg/L TiO\({}_{2}\) NPs [247]. TiO\({}_{2}\) NPs (43 nm) coated in gel, which were mixed with the seeds of pepper using doses 50, 100, and 150 mg/L, accelerated germination and enhanced lengths, fresh and dry weights of seedlings compared to control, concentration of 100 mg/L TiO\({}_{2}\) NPs being the most effective [228]. Nanopriming of seeds with TiO\({}_{2}\) NPs (anatase) (10-40 mg/mL) considerably enhanced germination as well as morphological characteristics and Chl content of _Petroselinum crispum_ seedlings grown in vitro in MS medium, the dose of 30 mg/L being the most effective [248]. Exposure to 40 ppm TiO\({}_{2}\) NPs improved fennel seed germination time by 31.8% in comparison to the untreated control, while treatment with 40 ppm TiO\({}_{2}\) NPs improved dry weight compared to the untreated control [249]. On the other hand, [PERSON] and [PERSON] [250] reported that spraying of fennel plant with 6 ppm TiO\({}_{2}\) NPs enhanced Chl synthesis, which was reflected in improved photosynthesis. Foliar treatment of _Mentha piperita_ plants with TiO\({}_{2}\) NPs using a dose of 150 mg/L increased fresh and dry weights by 48% and 62.6%, and nitrate reductase and carbonic anhydrase activities 150 days after planting by 17.7% and 19.1%, respectively, compared to control plants; an increase of nitrogen content, stomatal conductance, and net photosynthetic rate by 12.6%, 8.5% and 23.8%, respectively, compared to the control plants, was observed as well. Diameter and density of peltate glandular trichomes, which are important from the aspect of EO production, were increase by 77.8% and 62.5%, respectively, at treatment with 100 mg/mL TiO\({}_{2}\) NPs [144]. _Mentha piperita_ L. and _Salvia officinalis_ L. plants exposed to TiO\({}_{2}\) NPs either via the leaves (using TiO\({}_{2}\) NPs suspension) or via the root system (in soil) resulted in reduced Chl contents in _M. piperita_ and _S. officinalis_ plants treated through root system, but not after application of NPs suspension on leaves of sag plants, likely due to the abundance of trichomes, providing a natural barrier for the NP accumulation to the symplast. In the soil-exposed plants translocation of uptaken TiO\({}_{2}\) NPs from roots to shoots resulted in reduced Chl levels. The reduction of Chl correlated mainly with the loss of Mg (sage) and Mn (peppermint) in treated plants [251]. Foliar application of 0.04% TiO\({}_{2}\) NPs improved the contents of total Chl, carotenoids, and soluble proteins, as well as grain yield of satfflower plants to greater extent than application of 0.02% TiO\({}_{2}\) NPs and bulk TiO\({}_{2}\)[252]. In contrast to smaller TiO\({}_{2}\) NPs of 50 nm, larger TiO\({}_{2}\) NPs of size 68 nm had beneficial effect on germination of _Ablomoschus esculentus_ seeds. However, the small-sized TiO\({}_{2}\) NPs applied at a dose of 200 mg/kg pronouncedly increased Chl\(a\) and total Chl content compared to the control; a dose of 800 mg/kg considerably increased fresh weight of plants compared to the control. On the other hand, both types of NPs reduced APX in roots and leaves, whereas GR activity in roots decreased, but increased in the leaves. A considerable raise of SOD activity in roots and leaves of plants exposed to TiO\({}_{2}\) NPs signalized their phytotoxic impact. Moreover, treatment with TiO\({}_{2}\) NPs caused a size-dependent and dose-dependent decrease in essential minerals Ca, Mg, and Fe contents in fruits, as well as adversely altered the proximate compositions (except carbohydrate) of fruits [253].