Drought stress and TiO2 nanoparticles affect the composition of different active compounds in the Moldavian dragonhead plant

Abstract

The effects of three levels of drought stress [100%, 75% and 50% field capacity (FC)] and different concentrations of TiO2 nanoparticles (0, 5, 10, 20, 30, 50, 100, and 150 ppm) were assessed on the different metabolites of Moldavian dragonhead plant, an important ornamental, medicinal and aromatic herb. Results of high-performance liquid chromatography analysis of Moldavian dragonhead extract showed that among 14 detected compounds in the chromatogram, rosmarinic acid was the most frequent and followed by chlorogenic acid, acacetin-7-O-glucoside and apigenin-7-O-glucoside. Drought stress affected some of the metabolites and the highest values of rosmarinic, chlorogenic and p-cumaric acids were recorded in the moderate drought stress (75% FC), while in the higher drought stress (50% FC) some compounds such as caffeic acid and apigenin were increased and some other including ellagitannin and gentisic were decreased. Plant dry weight was also decreased under drought stress while essential oil content was increased. Production of studied metabolites was also influenced by application of TiO2 nanoparticles. Among different concentrations of TiO2 nanoparticles, 30, 50 and 100 ppm showed to be the most effective concentrations. Although TiO2 treatment did not significantly affect plant dry weight, the essential oil content was increased by this treatment and the highest value was obtained after treatment with 30 ppm of TiO2. According to our results, both drought stress and TiO2 nanoparticle treatments are able to increase some valuable phenolic substances including rosmarinic acid and chlorogenic acid in Moldavian dragonhead plant. Altogether, drought stress at 75% FC and TiO2 nanoparticles at concentrations of 30–50 ppm can increase phenolic bioactive compounds of Moldavian balm. New findings possibly would suggest a practical application of controlled drought stress and TiO2 nanoparticles in the culture of Moldavian balm with the purpose of increasing phenolic compounds.