The search towards cyto-embryological and physiological obstacles in sexual reproduction of Stevia rebaudiana Bertoni

Seed germination in Stevia rebaudiana is poor and seedlings are difficult to achieve, thus the generative reproduction of this plant is limited. The aim of our studies was to investigate the stages of female and male gametophyte development along with pollen viability and pollen germination. Although our results showed the proper way of stevia male and female gametophyte development and a high viability of mature pollen grains, the lack of pollen tube formation followed by difficulties in seed development were still observed. We hypothesize that trouble with propagation of S. rebaudiana by seed might be caused by the unsuitable level of gibberellins (GAs) that are commonly recognized as signaling factors during the transition from the vegetative to the generative developmental phase. We found the decrease in the concentration of some GAs during plants flowering and we concluded that this might cause the inability of pollen tube germination. Moreover, S. rebaudiana plants exhibit a high concentration of steviol glycosides (SGs) that are synthesized in the biosynthetic pathway sharing some steps with the GAs formation. Therefore, the redirection of the metabolic pathway into secondary metabolites biosynthesis might be a reason for the failure in stevia pollen grains proper function.

Automated summary

Seed germination in Stevia rebaudiana is poor, limiting generative reproduction. The study suggests that improper levels of gibberellins and redirection of metabolic pathways for secondary metabolites biosynthesis may cause difficulties in pollen tube germination, affecting seed development in the plant.