Titanium dioxide nanoparticles improve element uptake, antioxidant properties, and essential oil productivity of Melissa officinalis L. seedlings under in vitro drought stress

In vitro drought stress has a considerable impact on the mass production of active compounds in medicinal plants. Nevertheless, photosynthesis, nutrient uptake, and protein synthesis may be negatively affected by drought, which results in poor growth. Titanium dioxide nanoparticles (TiO2 NPs) have recently been shown to play an important role in increasing nutrient uptake, resistance to various environmental stresses, and better plant growth. Regarding the importance of pharmaceutical metabolites of Melissa officinalis L., this experiment aimed to assess the role of TiO2 NPs in improving physiological responses and phytochemical properties in M. officinalis under in vitro drought stress. For this, two-week-old seedlings were cultured on Murashige and Skoog (MS) medium supplemented with 0, 50, and 100 mg L-1 TiO2 NPs and 0, 3, and 6% (w/v) polyethylene glycol (PEG). Two weeks after treatments, a reduction of chlorophyll, protein content, essential elements, and enhancement of H2O2 and malondialdehyde (MDA) levels were seen as a result of drought stress. It was observed that M. officinalis partially responded to the drought by increasing non-enzymatic antioxidants, including phenolics, flavonoids, and anthocyanin and ascorbate peroxidase activity. Moreover, PEG-induced drought stress increased some important essential oil content such as limonene, alpha-pinene, myrcene, γ-3-carene, citral, and carvacrol; however, the results showed that TiO2 NPs not only increased the quantity of essential oils but also led to tolerance to the drought stress by increasing photosynthetic pigments, antioxidant systems, absorption of essential nutrients, and decreasing H2O2 and MDA levels.

Synthesis of magnetic nanoparticles and their effects on growth and physiological parameters of Calotropis procera seedlings

The present study was carried out to elucidate effects of synthesized magnetic nanoparticles (MNPs) on morphological and physiological parameters and main essential oil components of Calotropis procera seedlings. For this purpose, 21-day-old seedlings grown under hydroponic conditions were treated by the different MNP concentrations (0, 50, 100, 150, and 200 mg L^-1). The results showed that the growth parameters, chlorophyll pigments, soluble sugars, and total proteins significantly increased in leaf under MNP treatment, except for the root length. As compared to the control, MNPs induced a substantial change in the activities of antioxidant enzymes, H₂O₂, and malondialdehyde contents. Ascorbate peroxidase activity showed a meaningful increase in leaf treated with 200 mg L^-1 MNPs, while superoxide dismutase activity and concentration of H₂O₂ conspicuously decreased relative to the control. Moreover, MNPs enhanced geranial, 1,8-cineol, a-phellandrene, citronellal, camphor, and terpinen-4-ol contents as major components. These results suggest that MNPs could be a promising method of iron application in agricultural systems. Regarding the effects of MNPs, 200-mg L^-1 MNPs were most effective on the production of main essential oils and plant growth that could serve as a favorable elicitor for plant improvement.