Effects of TiO 2 Nanoparticles on Activity of Antioxidant Enzymes, the Expression of Genes Involved in Rosmarinic Acid Biosynthesis and Rosmarinic Acid Content in Dracocephalum kotschyi Boiss

Dracocephalum kotschyi Boiss has been known as a valuable source of rosmarinic acid (RA), a multifunctional phenolic bioactive compound. In this study, a greenhouse experiment was arranged to investigate the effect of nano-TiO2 on phenol and flavonoid contents, phenylalanine ammonia-lyase (PAL), superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activities and genes expression levels of phenylalanine ammonia-lyase (PAL), tyrosine aminotransferase (TAT), and rosmarinic acid synthase (RAS) which is involved in RA biosynthesis. The content of RA was also determined at plant leaves by high performance liquid chromatography (HPLC). Plants were exposed to nano-TiO2 with the concentrations of 0, 50, 300, 700 and 1000 mg/L. Data analysis revealed the highest activity of PAL and total phenol content at 700 mg/L nano-TiO2. The maximum activity of CAT and SOD enzymes was observed at 700 mg/L while the activity of APX reached the highest at 1000 mg/L. All applied concentrations of nano-TiO2 significantly decreased PAL expression except 700 mg/L, which did not change its expression. The highest expressions of TAT and RAS genes, compared to control plants, were observed at 700 mg/L concentration of nano-TiO2. The RA content also reached to maximum at this concentration of nano-TiO2. The observed congruence between PAL, TAT, and RAS expressions and RA content in D. kotschyi plants treated with nano-TiO2 suggested that the content of RA in D. kotschyi can be enhanced through up-regulation of the genes responsible for its biosynthesis by application of the TiO2 nanoparticles as robust inducers.