Effect of plant growth regulators and explants on callus induction and study of antioxidant potentials and phenolic metabolites in Salvia tebesana Bunge

This study was undertaken to investigate the effect of different plant growth regulators (PGRs) on callus induction in Salvia tebesana explants grown in vitro and to evaluate the content of secondary phenolic compounds and their antioxidant potential. The explants (shoot apical meristem, leaf and petiole) were dissected from an 8-week-old plant of S. tebesana growing in vitro and cultured on MS media containing different concentrations of 2,4-D (0, 0.5, 1, 1.5 and 2 mg L-1), NAA (0, 0.5 and 1 mg L-1) and BAP (0, 0.5 and 1 mg L-1), either alone or in a blend with each other. Morphological characteristics of the callus (consistency and colour), biomass increase based on fresh and dry weight and the percentage of induction were recorded after 56 days. Levels of total phenols, ortho-diphenols, phenolic acids, flavonoids, proanthocyanidins and flavonols of callus, as well as antioxidant activities, were evaluated in vitro. The maximum callus formation (100%) was obtained from shoot apical meristem on MS medium supplemented with 0.5 and 1.5 mg L-1 2,4-D + 1 mg L-1 BAP and with 1 and 1.5 mg L-1 2,4-D + 0.5 mg L-1 BAP, whereas the highest fresh (15.06 +/- 0.88 g) and dry (0.33 +/- 0.02 g) weights of call were observed in a medium containing1.5 mg L-1 2,4-D + 0.5 mg L-1 NAA. It was noted that MS media augmented with combined PGRs had the highest accumulation of polyphenols, phenolic acids and flavonoid compounds, with levels of content varying in the following order: 2,4-D + BAP > NAA + BAP > 2,4-D + NAA. Strong linear correlations were established between total phenolic content of callus extracts and results of the DPPH and FRAP assays (r(2) = 0.896 and r(2) = 0.946, p < 0.01, respectively). The obtained results suggest that the described method could be utilised as a tool for large-scale Yproduction of medicinal metabolites of S. tebesana by tissue culture.