Exposure to TiO2 nanoparticles (NPs) and zeolite stimulates growth, physiology, and phytochemical characteristics and elevates Mentha piperita L. tolerance to salinity stress.

Soil salinity is a major environmental problem that affects plant growth and production. Peppermint, a member of the Lamiaceae family, is a widely used medicinal plant that has many applications in the food, cosmetic, and pharmaceutical industries. Therefore, it is important to identify new ways to improve the growth and production of secondary metabolites in mint plants. The current study was performed on peppermint plant to assess the impacts of zeolite (0, 2, and 4 g kg−1) and titanium dioxide nanoparticles (Nano TiO 2 , 0 and 100 mg L−1) in NaCl salinity (0, 100, and 200 mM NaCl) conditions in a factorial arrangement on the basis of a randomized complete block design (RCBD) three times. According to the results, salinity stress decreased root and shoot dry weight, relative water content (RWC), photosynthetic pigment contents, root and shoot K content, K/Na ratio of root and shoot, ion selectivity of K over Na, and increased Na ion content, H 2 O 2, and Malondialdehyde (MDA) contents. Also, salinity stress at the level of 100 mM increased proline, total phenol, flavonoid content, Phenylalanine ammonia-lyase (PAL) enzyme activity, and essential oil yield, but increasing the salinity level to 200 mM led to a decrease in morpho-physiological parameters. Nano TiO 2 and zeolite improved the shoot and root dry weight, root and RWC, shoot potassium content, K/Na ratio of shoot and root, Ion Selectivity (S K, Na), total phenol, flavonoid content, PAL enzyme activity, and essential oil yield, and decreased root and shoot sodium content, Na/Ca, H 2 O 2, and MDA content under salinity stress conditions. Salinity caused a significant (p ˂ 0.01) decrease in oxygenated monoterpenes, especially menthol, but led to an increase in menthone, menthofuran, and pulegone content. On the other hand, exposure to Nano TiO 2 and zeolite could increase the menthol content and decrease the menthone, menthofuran, and pulegone content under salinity stress. Thus, moderate salinity stress, zeolite, and 100 mg L−1 Nano TiO 2 foliar spray are suggested to get a greater yield and high-quality products in mint plants. According to the results of this experiment, the positive impacts of zeolite and Nano TiO 2 enhance both the quantity and quality output of essential oil, photosynthetic pigments, phenolic compounds as defense compounds, and potassium content as an osmotic regulator. [Display omitted] • The effect of zeolite and Nano TiO 2 under salinity stress was studied on the Mentha piperita L. plant's performance. • Zeolite and Nano TiO 2 application led to enhancement in the growth and photosynthetic pigments under 100 mM salt stress. • Zeolite and Nano TiO 2 resulted in an increase in the K/Na ratio, total phenol, and PAL enzyme activity under salt stress. • Nano TiO 2 and zeolite under salt stress augmented the essential oils content and main components of EO especially menthol. [ABSTRACT FROM AUTHOR]