Daminozide Enhances Vigor and Steviol Glycoside Yield of Stevia (Stevia rebaudiana Bert.) Propagated in the Temporary Immersion Bioreactor

Stevia (Stevia rebaudiana Bertoni) contains sweet compound widely used as natural sweetener, steviol glycoside (SG). SG is a diterpenoid secondary metabolite synthesized from ent-kaurenoic acid, the same precursor of Gibberellin (GA). Therefore, in this study, a GA inhibitor, Daminozide (0, 10, 20 ppm) was used to block ent-kaurenoic acid conversion towards GA synthesis in attempt to increase SG content of stevia propagated in Temporary Immersion Bioreactor (TIB). Daminozide in 10 mg/L was observed to be the optimum concentration which increased biomass weight and SG content (stevioside and rebaudioside A) up to 40%. The treatment also increased transcripts accumulation of genes enrolled in SG biosynthesis, such as SrKA13H, SrUGT85C2, and SrUGT76G1, indicating SG pathway become more active due to the inhibition of GA pathway. Furthermore, the inhibition of GA was also indicated by the upregulated expression of GA biosynthesis gene (GA3ox) as the result of feedback regulation, and the downregulated expression of GA catabolism gene (GA2ox2) as the result of feed-forward regulation caused by inhibitor treatment.