Effect of different concentrations of KH2PO4 on the expression of UGT85C2 and KO genes and some biochemical traits of Stevia Rebaudiana bertoni

Stevia rebaudiana bertoni is a natural sweetener that is sweeter than sugar; however it does not have any calorie and can be used for diabetic patients. The sweet taste of stevia is because of the steviol glycosides (SGs) accumulated in the leaves. Rebaudioside A-F and Stevioside are the main compounds of stevia. KO and UGT85C2 genes are two important genes involved in biosynthesis pathway of steviol and steviolmonoside that are precursors of other SGs. Due to the very low germination rate of stevia seeds, tissue culture is the fastest way for propagation of it. Therefore, optimizing the composition of the culture medium is necessary to increase of pharmaceutical ingredients in stevia. This experiment was conducted to study the effect of different concentrations of KH2PO4 (0, 4.25, 8.5, 17, 34 µM) on the expression of KO and UGT85C2 genes using semi- quantitative RT-PCR technique as well as soluble sugar content and antioxidant activity of stevia. Analysis of variance showed a significant difference between the treatments (p≤0.01) for all measured parameters. Mean comparison using LSD (p≤0.05) showed that UGT85C2 and KO genes possessed the highest expression level in 4.25 and 17 µM KH2PO4respectively. Also, the stevia showed the highest content of soluble sugars and antioxidant activity in 34 µM KH2PO4. According to our results it seems that total steviol glycosides increased after adding KH2PO4into the culture medium, but its effect on different glycosides was not the same and probably changed the ratio of different SGs in this plant.