metabolites to increase their performance upon exposure to various kinds of elicitors. The present study was undertaken to evaluate the impacts of various concentrations of nano-titanium dioxide (TiO2) particles, viz., 0, 10, 50, 100, 200 and 1000 mg l-1 on growth, biosynthesis of secondary metabolites such as essential oils, total phenolics, flavonoids and antioxidant efficacy of the extracts obtained from the treated Salvia officinalis plants, assayed using DPPH free radical scavenging and b-carotene/linoleic acid bleaching test systems. The results showed that the highest and the lowest dry weights of root and shoot tissues were obtained from plants exposed to 100 and 1000 mg l-1 TiO2, respectively. The highest total phenolic (35.2 mg GAE g-1 dry wt.) and flavonoid (21.9 mgCE g-1 drywt.) contentswere obtained in plants exposed to 200 and 100 mg l-1 nano-TiO2, respectively. Gas chromatography and mass spectrometry analysis showed that the major components of essential oils were monoterpenes, including Camphene, p-Cymene, 1,8-Cineol, Cis-Thujene and Camphor. The highest value of Cis-Thujene (34.5 %) and 1,8-Cineol (21.2 %) were achieved in extracts obtained from plants exposed to 200 mg l-1 nano-TiO2. However, the maximal content of Camphene (12.1 %) was obtained from plants exposed to 1000 mg l-1 nano-TiO2 treatment. Although the extract from all treated plants improved antioxidant activity, it was highest for the extract obtained from plants treated with nano-TiO2 at 200 mg l-1 with an IC50 value of 2.44 lg g-1 dry wt. as compared to that of control plants (6.42 lg g-1 dry wt.) and butylated hydroxytoluene as positive probe (3.68 lg g-1 dry wt.). It was suggested for the first time that nano-TiO2 may act as an elicitor to improve secondary metabolism in S. officinalis plants for biosynthesis of natural antioxidants.
