In vitro morphogenic response and metal accumulation in Albizia lebbeck (L.) cultures grown under metal stress

An efficient regeneration protocol for rapid mass propagation and uptake of heavy metals in Albizia lebbeck (L.), a fast growing, medicinally as well as economically important timber yielding tree was developed. Nodal segments derived from a 20-year-old tree were cultured on MS (Murashige and Skoog) medium supplemented with 10 mu M 6-Benzyladenine (BA) and 1 mu M alpha-Naphthalene acetic acid (NAA) showed optimum shoot regeneration frequency (76.6%), number of shoots (23.2 +/- A 0.28) per explant and shoot length (2.86 +/- A 0.08 cm) after 10 weeks of culture. After standardizing a reliable protocol for micropropagation, effects of ZnSO4 (0.06-0.48 mM), CuSO4 (0.02-0.2 mM) and CdCl2 (0.0001-0.001 mM) on shoot morphogenesis were also assessed. The regenerated shoots maintained on maintenance medium (MS + 10.0 mu M BA + 1.0 mu M NAA) containing ZnSO4 (0.06 mM) showed maximum response in terms of shoot number (24.5 +/- A 0.83) and length (5.9 +/- A 0.05 cm) after 10 weeks of culture. Proline content showed an increasing trend while chlorophyll (a and b) content exhibited decreasing trend with an increased metal concentrations compared to MM cultures, and maximum increase in proline and decrease in chlorophyll content was recorded in cultures grown on Cd-enriched medium. Best rooting was accomplished on half strength MS medium with 2.0 mu M IBA and ZnSO4 (0.06 mM). The plantlets thus obtained were successfully hardened and transferred to greenhouse with 75% survival rate and exhibited normal morphological characteristics compared to donor plant.