SiO 2 nanoparticles as elicitor for increased rebaudioside-A in Stevia rebaudiana micropropagated in solid and liquid cultures: a comparative study

The present study is aimed to study the effect of SiO 2 nanoparticles on in vitro morphogenesis and secondary metabolite biosynthesis potential of Stevia rebaudiana in solid and liquid culture media. Significant variations were recorded (in all the parameters) between plants regenerated on solid and liquid media, while no uniform pattern was obtained in the variations among different treatments. Morphological properties including shoot number (1.4 × to 1.8 × ), shoot length (1.7 × to 2 × ), node count (1.5 × to 1.8 × ), leaf area (2.6 × to 2.75 × ) and fresh weight (10.6 × to 14 × ) were higher in liquid cultures than solid cultures, irrespective of the SiO 2 NP treatment. However, some concentrations of SiO 2 NPs had positive impact on shoot morphology in both types of cultures increasing the parameters up to 2.4 folds in solid and 1.3 folds in liquid cultures. In case of biochemical parameters, inverse pattern was recorded such that chlorophyll and carotenoid contents were respectively 6 × to 10.6 × and 10 × to 12.5 × higher in solid cultures than in liquid cultures. Antioxidant activities also exhibited similar pattern which indicated higher stress in shoots regenerated on solid medium than on liquid medium. Further, content of reb-A was significantly higher in plants grown on solid medium than in liquid medium. In fact, the content increased up to 1.7 folds in the presence of SiO 2 NPs in solid medium, wherein the content decreased in presence of SiO 2 NPs in liquid medium. These findings provide first report which indicates that liquid cultures have growth promoting effect while in solid cultures the plants are comparatively under more stress even without any external stimuli and thus produce higher reb-A content. Moreover, SiO 2 NPs are likely to have different uptake and action mechanism in solid and liquid medium which needs further investigation to gain a deeper insight into the mechanisms responsible for these effects.