Plant Growth Regulators as Potential Elicitors to Increase the Contents of Phenolic Compounds and Antioxidant Capacity in Stevia Plants

Stevia rebaudiana Bertoni is mainly used as a sweetener in many countries without any reported negative effects on health. This species is also abundant in phenolic compounds, which makes this plant a good candidate to satisfy the growing demand of natural sources for sweeteners and antioxidant compounds. Exogenously applied plant growth regulators (PGRs), acting as elicitors, influence the biosynthetic pathways of secondary metabolites. In this context, methyl jasmonate (MeJa), spermidine (SPD), salicylic acid (SA), and paclobutrazol (PBZ) (100 µM) were applied to stevia plants growing in a hydroponic system to assess their effects on temporary changes (at 24, 48, and 96 h) of antioxidant capacity and phenolic compounds (total soluble phenols, flavonoids, and hydroxycinnamic acids) levels. Overall, it was observed that MeJa increased total soluble phenolic content and antioxidant activity in extracts from Stevia leaves. By contrast, the addition of SPD, SA, and PBZ did not show a significant increase in any of the evaluated parameters. The results also showed a positive and strong correlation between phenolic compounds contents and antioxidant capacity. In short, results suggest that the application of MeJa could be a feasible way to enhance the biosynthesis of high added value phytochemicals that have notable antioxidant properties, and consequently potential health benefits, in stevia plants.