In vitro propagation and iridoid analysis of the medicinal species Harpagophytum procumbens and H. zeyheri
Extracts of the tubers of Harpagophytum procumbens DC (Devil's Claw) are used widely for the relief of arthritis, lumbago and muscular pain. The anti-inflammatory activity has been attributed to their iridoid components. A two-step protocol was established for the in vitro propagation of plants of Harpagophytum sp. by the regeneration of new plantlets from nodal cuttings and their acclimatisation to ex vitro conditions. Single node cuttings were submitted to a root induction treatment with β-indoleacetic acid (5 days at 2 mg l–1) followed by a transfer to a phytohormone-free medium to promote root elongation and support plantlet development. The new plantlets were weaned under autotrophic conditions and subsequently acclimatised in a glasshouse where they grew into fertile flowering plants that produced the characteristic Devil's Claw fruits as well as tuberised roots. Analysis of the tuber tissue of the micropropagated plants showed the presence of the iridoids harpagoside and harpagide at concentrations comparable with those found in the wild plant material (1% dry weight). The leaves were also found to contain these iridoids, and therefore could potentially provide an alternative and more sustainable source of therapeutically active compounds. The application of in vitro methods for the propagation of Devil's Claw would contribute to the conservation of this species.
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