Effect of Methyl Jasmonate and Salicylic Acid on In Vitro Growth, Stevioside Production, and Oxidative Defense System in Stevia rebaudiana

To examine whether secondary metabolites in micro-propagated Stevia rebaudiana plants are enhanced, explants were cultured on the woody plant medium (WPM) supplemented separately with methyl jasmonate (MeJA) and salicylic acid (SA). Maximal shoot growth, root regeneration, and fresh and dry biomass accumulation were obtained on WPM containing 50 μM SA. Electrophoretic analysis of superoxide dismutase (SOD), peroxidase (POX), and catalase (CAT) in S. rebaudiana showed that three, two, and one isoforms were observed for SOD, POX, and CAT, respectively. The WPM containing MeJA and SA increased SOD and POX activities, especially those of SOD2 and POX1 isoforms, total phenolics and total antioxidant activity (DPPH; 1-1-diphenyl 2-picryl hydrazyl), and decreased CAT activity. The highest activities/levels of enzymatic and non-enzymatic antioxidants were observed in the WPM containing 100 μM SA. The high-performance liquid chromatography (HPLC) analyses showed that 50 μM MeJA and 100 μM SA supplementation enhanced stevioside production. The stevioside yield increased from 4.1 mg/g dry weight to 18.7 and 19.4 mg/g dry weight in in vitro plantlets exposed to 50 μM MeJA and 100 μM SA, respectively. The results showed that SA could regulate oxidative defense system and secondary metabolite production in micro-propagated S. rebaudiana.