Effects of methyl jasmonate, on stevioside and rebaudioside A content and expression of the ent-Kaurenoic acid 13-hydroxylase gene in Stevia rebaudiana Bert. in vitro

Glycosides are a form of secondary metabolites that consist variety compounds and in some cases can play a role in primary metabolism. Steviol is lipophilic skeleton of Stevioside and Rebaudioside A، two main glycosides of Stevia rebuadiana. Steviol glycosides which are synthesized in S. rebaudiana have important medical and nutritional values as high intensity natural sweeteners. Steviol is synthesized from Kaurenoic acid in chloroplastic Terpenoid pathway that mediated by Kaurenoic acid 13-hydroxylase. In this study، HPLC method and RT-PCR were performed for quantification of glycosides and gene expression (ent-Kaurenoic acid 13-hydroxylase) respectively. Methyl jasmonate treatment (at 20 micromolar) in vitro induced glycoside biosynthesis significantly (P≤0. 05) whereas higher concentration of Methyl jasmonate (100 µM) caused a decrease in glycoside production and growth. The most glycoside content of the plant was three days after treatment. Also Methyl jasmonate treatment caused an increase in ent-Kaurenoic 13-hydroxylase gene expression from 6 hours to 48 hours (after treatment) Results showed that biosynthesis of Stevia glycosides was probably a defense mechanism against pathogens and herbivore insects. Also we found that different concentrations of Methyl jasmonate، alter the ratio between glycosides rather than the increase in glycoside contents.