Abstract
Considering titanium dioxide nanoparticles (TiO2 NPs) role in plant growth and especially in plant tolerance against abiotic stress, a greenhouse experiment was carried out to evaluate TiO2 NPs effects (0, 50, 100 and 200 mg L−1) on agronomic traits of Moldavian balm (Dracocephalum moldavica L.) plants grown under different salinity levels (0, 50 and 100 mM NaCl). Results demonstrated that all agronomic traits were negatively affected under all salinity levels but application of 100 mg L−1 TiO2 NPs mitigated these negative effects. TiO2 NPs application on Moldavian balm grown under salt stress conditions improved all agronomic traits and increased antioxidant enzyme activity compared with plants grown under salinity without TiO2 NP treatment. The application of TiO2 NPs significantly lowered H2O2 concentration. In addition, highest essential oil content (1.19%) was obtained in 100 mg L−1 TiO2 NP-treated plants under control conditions. Comprehensive GC/MS analysis of essential oils showed that geranial, z-citral, geranyl acetate and geraniol were the dominant essential oil components. The highest amounts for geranial, geraniol and z-citral were obtained in 100 mg L−1 TiO2 NP-treated plants under control conditions. In conclusion, application of 100 mg L−1 TiO2 NPs could significantly ameliorate the salinity effects in Moldavian balm.
Highlights
Moldavian balm (Dracocephalum moldavica L.), a perennial herb of the Lamiaceae family and native to central Asia, naturalized in central and eastern Europe and is cultivated around the world as a medicinal plant
The tolerance mechanisms of plants to salinity stress are different in terms of osmotic regulation, CO2 assimilation, toxic ion uptake, ion compartmentation and/or exclusion, chlorophyll content, chlorophyll fluorescence, reactive oxygen species (ROS) generation, antioxidant defenses and photosynthetic electron transport[4,7]
Several reports have presented the negative and toxic effects of high concentration of TiO2 in plants that varied between plant tissues, growth stages and plant species based on concentrations and properties of nanoparticles[14,16]
Summary
Moldavian balm (Dracocephalum moldavica L.), a perennial herb of the Lamiaceae family and native to central Asia, naturalized in central and eastern Europe and is cultivated around the world as a medicinal plant. Salinity stress causes major problems regarding plant growth, development and productivity, especially in arid and semi-arid regions of the world[5] manifested as changes in morphological, physiological and biochemical characteristics of plants, ion toxicity (Na+ and Cl−), nutritional disorders and osmotic stress These negative impacts significantly decrease plant www.nature.com/scientificreports yield under salinity stress conditions[6]. TiO2 could be considered as a stimulant for plants that activates different defense mechanisms involved in plant tolerance against various abiotic stress factors[11] These effects might vary under different environmental conditions or in diverse plant species and based on the applied concentrations[14,15]. The present study tried to investigate beneficial and toxicological impacts of different concentrations of TiO2 NPs in nutrient solution on key morphophysiological and biochemical characteristics as well as essential oil profile in Moldavian balm, an aromatic and medicinal plant, grown under salinity stress conditions. The uptake and aggregation of TiO2 NPs in the plant root was investigated by epifluorescence microscopy
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