Shoot proliferation and rooting treatments influence secondary metabolite production and antioxidant activity in tissue culture-derived Aloe arborescens grown ex vitro

Aloe species are valuable plants with great ornamental and medicinal value. Although micropropagation protocols have been developed to meet the increasing global demand, the effects of the series of events during micropropagation on the phytochemical and pharmacological efficacy of ex-vitro plants remains poorly understood. Thus, we evaluated the effects of cytokinin and rooting compounds used during the shoot regeneration and rooting phases respectively, on secondary metabolite production in greenhouse-grown in vitro-derived Aloe arborescens. Shoots derived from meta-methoxytopolin (MemT)-containing medium and rooted with either smoke-water (SW) or indole butyric acid (IBA) had higher levels of total phenolics and flavonoids than those rooted on plant growth regulator (PGR)-free medium. Iridoid content was significantly reduced in cytokinin-regenerated shoots rooted with IBA in comparison to PGR-free regenerated shoots rooted with IBA. Conversely, the use of SW for rooting in cytokinin-regenerated shoots significantly increased iridoid content when compared to PGR-free regenerated shoots rooted with SW. These findings suggest an antagonistic interaction between cytokinins used in this study and IBA as well as a possible synergistic or additive interaction of the cytokinins with SW on iridoid production. Significantly higher antioxidant activity was recorded in shoots regenerated from meta-topolin riboside (mTR) and MemT and rooted with IBA or SW when compared to those rooted without PGR. Overall, the type of cytokinin and rooting treatments individually and interactively had a significant carry-over effect on secondary metabolite production and antioxidant potential of tissue culture-derived A. arborescens. Therefore, when micropropagating plants for medicinal uses, it is prudent to select the right cytokinin and rooting compound for optimal production of secondary metabolites and ultimately the pharmacological efficacy of acclimatized plants.