# Responses of Medicinal and Aromatic Plants to Engineered Nanoparticles +
## 4 Effect of Metal-Based NPs on Medicinal and Aromatic Plants
### TiO\({}_{2}\)-Based NPs
#### 4.5.3 Attenuation of Abiotic Stress  
Treatment of _Verbuscum sinuatum_ plants exposed to artificial drought conditions (\(-0.6\) MPa) with 20 ppm TiO\({}_{2}\) was found to mitigate negative impact of water deficit on growth characteristics and contents of assimilation pigments by stimulation of antioxidant defense systems, resulting in improved drought tolerance [260]. Foliar application of 10 ppm TiO\({}_{2}\) NPs increased shoot dry mass and EO content of _Dracocephalus moladavica_ L. plants and in plants exposed to drought stress. Plants grown under water deficit, which were treated with 10 ppm TiO\({}_{2}\) NPs, had more proline and considerably lower content of H\({}_{2}\)O\({}_{2}\) and MDA compared to untreated plants, suggesting that TiO\({}_{2}\) NPs can mitigate water deficit-induced oxidative damages. On the other hand, assimilation pigments in leaves were pronouncedly reduced in _Dracocephalus moladavica_ plants treated with 10 ppm TiO\({}_{2}\) NPs [261]. Whereas spraying with TiO\({}_{2}\) NPs positively affected growth of _Thymus vulgaris_ cultivated under drought stress, it did not affect the components of EO [262].  
TiO\({}_{2}\) NPs (2 and 5 ppm) increased tolerance of _Glycyrrhizza glabra_ L. plants to cold stress, reduced MDA and H\({}_{2}\)O\({}_{2}\) levels in cold-stressed (4 \({}^{\circ}\)C) plants, resulting in lesser oxidative damage, and increased the contents of phenolics, total protein, and osmolytes [263]. Treatments of sensitive and tolerant chickpea genotypes with TiO\({}_{2}\) NPs did not induce oxidative damage in plans, which were able to mitigate membrane damage and electrolyte leaching, and pronouncedly reduce MDA content also under cold stress conditions via improved redox status of the genotypes, with a concentration of 5 ppm TiO\({}_{2}\) NPs being the most effective [264].  
Everyday spraying with TiO\({}_{2}\) NPs at doses 25 and 50 mg/L was found to prevent _Crocus sativus_ L. plants cultivated hydroponically against harmful effects on morphological characteristics of plants caused by UV irradiation (30 and 45 min daily for one month). Combined treatment reduction of dissolved sugars, increased levels of total anthocyanins and MDA in leaves, as well as higher radical scavenging activity were observed; a raise in TPC and TFC in saffron stigmas was estimated as well, which could contribute to enhanced nutritive value of saffron [265].  
TiO\({}_{2}\) NPs (anatase; 10-25 nm) were able to increase concentrations of assimilation pigment in leaves of flax under normal and water deficit conditions, reduce the levels of H\({}_{2}\)O\({}_{2}\) and MDA, resulting in lower degree of lipid peroxidation, particularly at a dose of 10 mg/L, and enhance seed oil and protein contents in treated plants [266]. In cell suspension cultures of flax exposed to 50, 100, and 150 mg/L TiO\({}_{2}\) NPs, increased activity of cinnyl alcohol dehydrogenase and maximum TPC content was observed at application of 150 mg/L TiO\({}_{2}\) NPs; TiO\({}_{2}\) NPs at tested concentrations increased the total lignin content as well [140].