Effects of cytokinins, gibberellic acid 3, and gibberellic acid 4/7 on in vitro growth, morphological traits, and content of steviol glycosides in Stevia rebaudiana

Steviol glycosides (SGs) and gibberellic acids share a part of their biosynthesis pathways. Despite the widespread studies on the effect of gibberellic acid 3 (GA ₃ ), the effect of gibberellic acid 4 and 7 (GA _4/7 ) on Stevia rebaudiana has never been studied. This study aimed at a comparative evaluation of different hormone effects, i.e., 1 mg L ⁻¹ GA _4/7 , 1 mg L ⁻¹ GA ₃ , or 0.5 mg L ⁻¹ kinetin and 0.5 mg L ⁻¹ 6-benzylaminopurine (BAP) (KB 0.5), on in vitro propagation, growth, morphological properties, and content of SGs in leaf samples of stevia. In comparison with the control group (hormone-free), the treatments of KB 0.5 or GA ₃ produced the highest biomasses and largest leaf areas. The three hormonal treatments produced a similar number of leaves, the ratio of fresh to dry weight, and leaf length. GA _4/7 -treated explants produced the highest ratio of leaf area to leaf length. The effect of GA _4/7 on shoot elongation was greater than that of the control or even GA ₃ . While the effect of GA ₃ on rebaudioside-A (Reb-A) production was similar to that of the control (16.2 and 18.04 mg g ⁻¹ , respectively), GA _4/7 resulted in a lower amount of it (13.31 mg g ⁻¹ ). Except for GA _4/7 , which induced more stevioside accumulation, the treatments’ effects were comparable to that of the control. The ratio of stevioside to Reb-A was the highest for GA _4/7 (2.62), followed by GA ₃ (1.93), and then the two others. Sum of Reb-A and stevioside content was not changed by the use of any of the treatments.