Improvement of shoot morphogenesis in vitro and assessment of changes of the activity of antioxidant enzymes during acclimation of micropropagated plants of Desert Teak

The aim of the study was to develop an improved and rapid regeneration system via axillary shoot proliferation for Tecomella undulata, an important endangered medicinal tree in India. The Murashige and Skoog (MS) medium augmented with different concentrations (0.1, 0.3, 0.5, 0.7, 1.0, 2.5, 5.0, 7.5 and 10.0 mu M) of Thidiazuron (TDZ) was tested for the ability to induce axillary shoot development from cotyledonary node explants excised from 7-day-old sterile seedlings. Among the tried concentrations of TDZ, 0.7 mu M showed optimum response in inducing maximum number (25.00 +/- A 2.30) of shoots and shoot length (4.06 +/- A 0.58 cm) after 3 weeks of incubation. The regenerated shoots when subcultured on MS medium lacking TDZ gave twofold shoot multiplication rate with maximum number (43.00 +/- A 2.86) of shoots per explant and longer shoot length (7.40 +/- A 0.34 cm) during the fourth subculture passage. Attempts were also made to study the morphogenetic effect of medium pH and sucrose concentration on axillary shoot induction and proliferation. The highest efficiency of shoot regeneration was recorded in MS medium supplemented with 0.7 mu M TDZ and 3% sucrose at pH 5.8 after 3 weeks of culture. Different concentrations of Indole-3-butyric acid (IBA) were tested to determine the optimum conditions for ex vitro rooting of microshoots. The best result was accomplished with IBA (200 mu M) pulse treatment given to the basal end of the microshoots for 30 min followed by their transfer in plastic cups containing soilrite and eventually established in natural soil with 80% survival rate. During acclimatization of plants, catalase (CAT) activity increased reaching maximum at 28th day after transplantation, while superoxide dismutase (SOD) activity increased reaching a maximum in the 21 days. Likewise, changes in the glutathione reductase (GR) and Ascorbate peroxidase (APX) were also detected. The observed changes reflect the plant's capacity to develop antioxidant mechanisms during acclimatization which determine the ability to survive in oxidative stress. The standardized protocol for mass propagation of Tecomella undulata should eliminate the dependence on natural stands of plants for pharmaceutical purposes, and will also serve as a means of conservation as the species is highly overexploited.