In vitro propagation, proscillaridin A production and antibacterial activity in Drimia robusta

Drimia robusta is a threatened traditional medicinal plant extensively used in South Africa. Rapid in vitro mass propagation of the species was developed for commercial cultivation from leaf explants using various concentrations and combinations of plant growth regulators and organic elicitors. The highest number of regenerated shoots per explant (14.6 +/- A 0.54) was obtained on Murashige and Skoog (MS) medium supplemented with a combination of 2.27 mu M thidiazuron (TDZ), 2.22 mu M benzyladenine (BA) and 20 mu M glutamine. Adventitious shoots were rooted and the plantlets were successfully acclimatized (100 %) in a vermiculite-soil mixture (1:1 v/v) in the greenhouse. Proscillaridin A (PsA) content and the antibacterial activity of in vitro and ex vitro regenerated plants were evaluated in different tissues in comparison to naturally-grown plants. The highest content of PsA (19.68 mu g mg(-1) DW) was recorded in roots of ex vitro plants which were grown on MS medium containing 2.27 mu M TDZ, 2.22 mu M BA and 100 mg l(-1) casein hydrolysate. In vitro regenerated plants grown on MS medium containing 2.27 mu M TDZ, 2.22 mu M BA and 50.8 mu M MBZ gave high antibacterial activity (MIC of 0.156 mg ml(-1)) against both Gram-positive and Gram-negative bacteria. Using this protocol the regenerated plants can be used in traditional medicine as an alternative to naturally collected plants.