De novo in vitro shoot morphogenesis from shoot tip-induced callus cultures of Gymnema sylvestre (Retz.) R. Br. ex Sm

BACKGROUND: Gymnema sylvestre is a medicinal woody perennial vine known for its sweetening properties and antidiabetic therapeutic uses in the modern and traditional medicines. Its over-exploitation for the therapeutic uses and to meet the demand of pharmaceutical industry in raw materials supply for the production of anti-diabetic drugs has led to considerable decline in its natural population. RESULTS: An efficient system of shoot bud sprouting from nodal segment explants and indirect plant regeneration from apical meristem-induced callus cultures of G. sylvestre have been developed on Murashige and Skoog (MS) medium amended with concentrations of cytokinins. Of the three growth regulators tested, N6-benzylaminopurine (BAP) was the most efficient and 2.0 mg L-1 gave the best shoot formation efficiency. This was followed by thidiazuron (TDZ) and kinetin (Kin) but, most of the TDZ-induced micro shoots showed stunted growth. Multiple shoot formation was observed on medium amended with BAP or TDZ at higher concentrations. The produced micro shoots were rooted on half strength MS medium amended with auxins and rooted plantlets acclimatized with 87% survival of the regenerates. CONCLUSIONS: The developed regeneration system can be exploited for genetic transformation studies, particularly when aimed at producing its high yielding cell lines for the anti-diabetic phytochemicals. It also offers opportunities for exploring the expression of totipotency in the anti-diabetic perennial vine.

Stress and defense responses in plant secondary metabolites production

In the growth condition(s) of plants, numerous secondary metabolites (SMs) are produced by them to serve variety of cellular functions essential for physiological processes, and recent increasing evidences have implicated stress and defense response signaling in their production. The type and concentration(s) of secondary molecule(s) produced by a plant are determined by the species, genotype, physiology, developmental stage and environmental factors during growth. This suggests the physiological adaptive responses employed by various plant taxonomic groups in coping with the stress and defensive stimuli. The past recent decades had witnessed renewed interest to study abiotic factors that influence secondary metabolism during in vitro and in vivo growth of plants. Application of molecular biology tools and techniques are facilitating understanding the signaling processes and pathways involved in the SMs production at subcellular, cellular, organ and whole plant systems during in vivo and in vitro growth, with application in metabolic engineering of biosynthetic pathways intermediates.

Enhanced in vitro Seedling Recovery in Nothapodytes nimmoniana (J. Graham) Mabberly.

Nothapodytes nimmoniana is an endangered medicinal tree and regarded most convenient natural source for large scale isolation of anticancer alkaloid camptothecin. In order to meet pharmaceutical market demand for camptothecin and conserve natural population of the species, in vitro culture techniques can be employed for mass propagation and production of the alkaloid. Seed germination is one of the difficult challenges in the establishment of the aseptic in vitro cultures. Pre-germination treatments of soaking in water, GA3 solution and aseptic excision of the embryo axis were employed to enhance seed germination and seedling recovery respectively for further in vitro studies. Seed soaking in water or GA3 solution for 24 hours enhanced the germination capacity with better response obtained when seeds were soaked in GA3 (2.6 μM) solution and germinated on half strength MS medium supplemented with the GA3. Removal of the outer, inner seed coat and inoculation of the embryo axis on medium amended with or without GA3 reduced seedling recovery time to 3-4 weeks. Seedlings obtained on medium fortified with GA3 showed vigorous growth with complete plantlet development than on PGR-free medium. The strategy can be employed to reduce seedling recovery time to within 3-4 weeks compared to 7-10 weeks required for germinating the seeds in vitro.