Differential effects of plant growth regulators on physiology, steviol glycosides content, and antioxidant capacity in micropropagated tissues of Stevia rebaudiana

Plants naturally produce secondary metabolites on exposure to abiotic/biotic stress. Production of secondary metabolites, like phenols or Flavonoids, is a defence mechanism against different stresses. This study explores the influence of plant growth regulators (PGRs) on the growth and secondary metabolites of in vitro grown tissues of zero calorie sweetener, Stevia rebaudiana. An efficient regeneration of this valuable plant under the influence of PGRs was conducted, and quantification of physiology parameters, steviol glycosides (SGs) and various antioxidant activities in callus, shoots and regenerated plants was performed. Significantly highest expiant response was achieved by 2 mg/L of 6-benzyl aminopurine (BAP) and 0.5 mg/L of 2,4-dichlorophenoxy acetic acid (2,4-D) combination in case of callogenesis, while shoot and root organogenesis was best illustrated by control and 0.5 mg/L of indole acetic acid (IAA) treatment, respectively. Regarding SGs formation in leaves, significantly greater content (2.07% and 0.93%) was obtained by control in case of rebaudioside A (Reb A) and 2 mg/L of BAP in case of stevioside (ST). Leaves of rooted-shoots produced significantly highest Reb A (4.21%) and ST (2.22%) content in case of 1 mg/L of IAA and 0.25 mg/L of IAA inoculation in Murashige and Skoog growth medium, respectively. Similarly, differential effects of PGRs were elucidated in case of all in vitro grown tissues on antioxidant properties. The study concludes that secondary metabolites can be efficiently produced in in vitro culture so can be employed in bioreactors.