This work describes the tissue culture of Plectranthus ornatus Codd. (Lamiaceae) on Murashige and Skoog (MS) medium with naphthalene acetic acid (NAA) (1.0, 2.0 and 4.0 mg L-1) and 6-benzylaminopurine (BAP) (1.0, 2.0 and 4.0 mg L-1) as growth regulators to obtain the overproduction of rosmarinic acid. The content of rosmarinic acid and its biosynthetic precursors were determined by high performance liquid chromatography (HPLC). The antioxidant activities (AA) of the extracts were also evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. The best growing condition was observed with the addition of 1.0 mg L-1 of both NAA and BAP in the culture medium yielded an increase of 94 times of rosmarinic acid comparing with the wild plant. All extracts diplayed antioxidant activity, as evidenced by the DPPH free radical scavenging assay. However, those with 2.0 mg L-1 NAA and, 1.0 mg L-1 NAA and BAP in culture medium showed the lowest EC50 (26.0 and 29.8 µg mL-1, respectively). At concentration higher than 10 µg mL-1 of rosmarinic acid it was not observed the correlation with AA, suggesting some other anti-oxidant mechanism acting.
Keywords:
rosmarinic acid; Plectranthus ornatus; in vitro tissue culture; caffeic acid
