High-frequency direct shoot regeneration from Drymaria cordata Willd. leaves

An efficient and reproducible procedure is described for direct shoot regeneration in Drymaria cordata Willd. using leaf explants cultured on Murashige and Skoog (MS) medium supplemented with α-naphthalene acetic acid (NAA) and 6-benzyladenine. The regeneration frequency varied with the plant growth regulator concentrations, orientation of the explants, and the carbon source and basal salts present in the regeneration medium. The highest mean number of shoots per explant (10.65 ± 1.03) was recorded on MS plates containing 3% sucrose and 0.8% agar supplemented with 0.1 mg/l NAA and 1.0 mg/l BAP. Shoot buds were induced in the basal parts of the leaf explants. Concentrations of NAA exceeding 1 mg/l suppressed shoot regeneration. Explants bearing the entire lamina and petiole were much more responsive than those having only the lamina. The plantlets that regenerated from the leaf explants were rooted successively on MS medium alone or in combination with indole butyric acid (IBA). The highest mean number of root organogenesis, with 25.67 ± 3.68 roots per leaf segment, was obtained in the presence of 1 mg/l IBA. Histological investigations of the regenerating shoots showed that the shoot buds had emerged from epidermal cells without callus formation. More than 90% of the in vitro-propagated plants survived when transferred to a greenhouse for acclimatization. Thus, this optimized regeneration system may be used for rapid shoot proliferation and genetic transformation.