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Abstract
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Among the metals contaminants, cadmium (Cd) is one of the most toxic elements in cultivated soils,
causing loss of yield and productivity in plants. Recently, nanomaterials have been shown to mitigate
the negative consequences of environmental stresses in different plants. However, little is known
about foliar application of titanium dioxide nanoparticles (TiO 2 NPs) to alleviate Cd stress in medicinal
plants, and their dual interactions on essential oil production. The objective of this study was to
investigate the effects of foliar‑applied TiO 2 NPs on growth, Cd uptake, chlorophyll fluorescence,
photosynthetic pigments, malondialdehyde (MDA) and hydrogen peroxide (H 2 O 2 ) contents, total
phenols, anthocyanins, flavonoids, antioxidant enzymes (SOD, CAT and POD) activity and essential
oil content of Mentha piperita L. (peppermint) under Cd stress. For this purpose, plants were grown
in Cd‑contaminated (0, 20, 40, and 60 mg L −1 ) soil, and different concentrations of TiO 2 NPs (0, 75,
and 150 mg L −1 ) were foliar sprayed at three times after full establishment until the beginning of
flowering. Exposure to TiO 2 NPs significantly (P < 0.01) increased shoot dry weight (37.8%) and
the number of lateral branches (59.4%) and decreased Cd uptake in plant tissues as compared to
the control. Application of TiO 2 NPs increased the content of plastid pigments, and the ratio Fv/Fm
(13.4%) as compared to the control. Additionally, TiO 2 NPs reduced the stress markers, MDA and
H2 O 2 contents and enhanced the activity of the phenylalanine ammonia‑lyase (PAL) enzyme (60.5%),
total phenols (56.1%), anthocyanins (42.6%), flavonoids (25.5%), and essential oil content (52.3%)
in Cd‑stressed peppermint compared to the control. The results also demonstrated that foliar spray
of TiO 2 NPs effectively improved the growth and chlorophyll fluorescence parameters and reduced
Cd accumulation in peppermint, which was mainly attributed to the reduction of oxidative burst and
enhancement of
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