Regeneration in Rheum emodi Wall.: A step towards conservation of an endangered medicinal plant species

Shoot buds emerged from intact leaves while still attached to plants after 60 days, without subculturing, on Murashige and Skoog (MS) medium containing 10.0 mu M 6-benzylaminopurine and 5.0 mu M indole-3-butyric acid. Histological studies revealed the emergence of shoot buds directly from the leaf Surface without an intervening callus phase. Regenerated plantlets were successfully transferred to the greenhouse after rooting in plant growth regulator-free MS medium. The survival percentage of transferred plants was very low. However, pretreatment of the plants at low temperature (15 +/- 2 degrees C) for 10 days before transfer to greenhouse conditions increased the survival percentage. The increased survival was supported by an increased number of vascular bundles, leaf thickness, net rate of photosynthesis (P-N), stomatal conductance (g(s)) and density (SD). The direct regeneration method from intact leaves of R. emodi will reduce the cost, time and labor required and hence can be successfully employed for faster in vitro multiplication and conservation of this endangered and medicinally important plant species.