Tissue culture mediated biotechnological interventions in medicinal trees: recent progress

Many tree species are an excellent source of a wide range of bioactive compounds of pharmaceutical importance. However, overexploitation of medicinal trees to fulfil the demand for plant-based herbal drugs puts pressure on its natural population. Therefore, many tree species are declining continuously, particularly those used in pharmaceutical industries. In addition, limited production of secondary metabolites from a specific part and only at a particular developmental stage and sometimes very-low yield are some major bottlenecks when secondary metabolites are isolated directly from a tree species. Tissue culture-based biotechnological interventions for propagation, in vitro conservation and secondary metabolite production in medicinally important tree species have been practiced during the last two-three decades. Many medicinally important trees successfully propagated in vitro through different modes of regeneration i.e., axillary shoot proliferation, adventitious organogenesis and somatic embryogenesis. Success in in vitro propagation of most of the medicinal trees has been achieved through axillary shoot proliferation. Recent studies on medicinal trees showed that ex vitro rooting is an ideal method of rooting of microshoots. Gene targeted molecular markers have now been preferred for genetic fidelity of tissue culture-raised plants of medicinal trees. In recent years, newly developed droplet-vitrification and cryo-plate methods increased the applicability of cryopreservation for the long-term conservation of many medicinal trees. Several bioactive compounds of pharmaceutical importance are produced from trees via in vitro culture technique. There are a few success stories of producing secondary metabolites at a commercial scale from medicinal trees i.e., taxol, camptothecin and azadirachtin. This review paper presents the recent progress on plant tissue culture-mediated biotechnological advances in medicinal trees, emphasizing different aspects of in vitro propagation, conservation, and production of bioactive compounds of pharmaceutical importance.