The present research studied biochemical responses and expression of two important genes in the biosynthetic pathway of steviol glycosides (SGs) of stevia at various levels of salicylic acid (SA) (0, 25, 50, 75 and 100 mM) and of yeast extract (YE) (0, 1, 2, 3 and 5 g/L) under different tissue culture conditions using a completely randomized design with three replications. After 4 weeks of culture, biochemical properties including H₂O₂, soluble carbohydrates, DPPH, total phenol and total protein contents and expression levels of the DXS and CPPS genes were measured. The results of ANOVA showed that both SA and YE had significant effects on all the studied biochemical traits. There was a linear relationship between DPPH and total phenol contents so that their highest amounts were recorded at 100 mM SA and 5 g/L YE. The highest contents of soluble protein and soluble carbohydrates were recorded at 75 mM and 3 g/L concentrations of the two elicitors. The results of gene expression studies indicated that the elicitors had positive effects on expression levels of the genes. Their highest expression levels were recorded at 50 mM SA and 2 g/L YE. We can conclude from these results that the use of SA and YE is a suitable method for increasing biosynthesis of the bioactive compounds in stevia.

Keywords: Elicitor, Gene expression, In vitro culture, Phenolic components, Soluble carbohydrate, Stevia

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