Effect of Growth Regulators and Culture Conditions on Direct Root Induction of Rauwolfia serpentina L. (Apocynaceae) Benth by Leaf Explants

Purpose: Rauwolfia serpentina (L.) Benth, from the family, Apocynaceae, is an important medicinal plant due to the alkaloid content of its root. The purpose of this study was to obtain roots directly from leaf explant using growth regulators. Methods: The leaf explant was inoculated on MS (Murashige and Skoog) medium supplemented with single and combinations of growth regulators. Root growth was also observed on liquid MS medium and under dark conditions. The reserpine content of the roots obtained was determined by HPLC. Results: Two combinations of auxins namely, para-amino benzoic acid (PABA) + α-naphthalene acetic acid ( NAA), and 3-Indole butyric acid (IBA) + NAA, promoted better root growth compared to single auxin treatment. The highest number of roots and regeneration response was observed on leaf explant cultured on MS media supplemented with PABA (1 mg l -1 ) + NAA (4 mg l -1 ). Liquid MS media gave slower growth, reduced number of roots, shorter root length as well as absence of reserpine, using the same combination of growth regulators, compared to solid MS media. The culture incubated under dark conditions produced thin roots. HPLC analysis of the regenerated roots indicated low alkaloid (reserpine) content (0.01 – 0.03). However, higher alkaloid content (0.03%) was observed in cultures with fewer numbers of roots. Conclusion: A simple and reliable protocol for direct induction of roots from leaf explant of R. serpentina using plant growth regulators has been developed.