In vitro plant regeneration, secondary metabolite production and antioxidant activity of micropropagated Aloe arborescens Mill

Aloe species are highly-prized for their ornamental value and have been utilized for centuries in traditional medicine. Due to their habitat loss and exploitation for medicinal and ornamental plant trade, many species in this genus have become threatened. One of the most important globally rated medicinal species in Aloe genus is A. arborescens. The current study evaluated the roles of different aromatic cytokinin types and concentrations on direct organogenesis, in vitro bioactive secondary metabolite production and antioxidant activity of regenerated shoots of A. arborescens. There was an increase in the number of adventitious shoots produced per explant with an increase in concentration in cultures treated with meta-topolin (mT), meta-topolin riboside (mTR), meta-methoxytopolin (MemT) and benzyladenine riboside (BAR), reaching an optimum at either 5.0 or 7.5 mu M. Overall, the treatment with 5.0 mu M mT gave the largest number of transplantable shoots (regenerated shoots with length greater than 10 mm). Rooted shoots were successfully acclimatized after 8 weeks with a survival frequency above 90 % and no observable morphological abnormalities. Variable amounts of total iridoids, phenolics, flavonoids and condensed tannins were detected in regenerated shoots from all the cytokinin treatments. An increased free-radical scavenging activity with an increase in concentration was recorded in regenerated shoots from mT and mTR treatments, reaching an optimum at 7.5 mu M concentration. The present study shows that the choice of cytokinin type and concentration exogenously supplied during tissue culture markedly influences not only shoot proliferation but also the in vitro production of bioactive secondary metabolites.