The effect of titanium oxide nanoparticles on the gene expression involved in the secondary metabolite production of the medicinal plant periwinkle (Catharanthus roseus)

Medicinal plant periwinkle with the scientific name Catharanthus roseus is an important source of anticancer and antihypertensive alkaloids. Due to the high price of these metabolites and their small content in periwinkle plant, tissue culture techniques have been suggested to increase their production. Therefore, this study was carried out with the aim of evaluating the effect of titanium oxide nanoparticles (TiO2) on the expression of key genes of the biosynthetic pathway of important medicinal constituents in periwinkle.
 
Murashige and Skoog (MS) medium was used as the basic medium along with 2,4-D (1 mg/L) and BAP (0.5 mg/L) plant growth regulators for leaf cultivation, callus induction, and cell suspension production. Periwinkle suspension culture was treated with concentrations of 0, 50, and 100 mg/l TiO2 nanoparticles at the peak of cell growth. Then, the expression of STR, SGD, DAT, and PRX genes was measured 24, 48, and 72 h after the treatment by Real-Time PCR. Tetrazolium test was also used to measure cell viability.
 
Although there was no significant difference between the percentage of cell viability after 50 and 100 mg/L NP-TiO2 treatment; however, the passage of time (from 24/48 h to 72 h) caused a decrease in cell viability. The application of a higher concentration of nanoparticles increased the expression of the key genes involved in the biosynthetic pathway of indole alkaloids. This increase continued up to 48 h after treatment, but then reduced. The highest expressions of STR, SGD, DAT, and PRX genes were obtained by 290, 186, 193, and 287% increase, respectively, in 48 h after the treatment of 100 mg/l TiO2 nanoparticles (as the most effective treatment with the highest percentage of cell viability).
 
In the face of TiO2 nanoparticles, as an elicitor and stress-causing agent, the expression of the genes involved in the biosynthesis of indole alkaloids is induced to achieve defense against the stressful agent and then the expression of the genes decreases after the passage of time and reduction of stressful symptoms. In general, the concentration of 100 mg/l TiO2 and the extraction of metabolites in 48 h after the treatment can be introduced as a promising stimulus to increase the content of indole alkaloids. According to the results, it is suggested that the exact mechanism involved in this metabolite increase be further investigated.