Exploitation of invitro cultures of Indian madder (Rubia cordifolia.Linn) for anticancerous compounds

Abstract

The present investigation on “Exploitation of in vitro cultures of Indian Madder (Rubia cordifolia L.) for anticancerous compounds” was carried out at the Plant Tissue Culture Laboratory of the Centre for Plant Biotechnology and Molecular Biology, College of Horticulture, Vellanikkara and Amala Cancer Research Centre, Thrissur during the period 2006-2008. The study was undertaken with the objective to standardize the in vitro techniques for initiation and proliferation of static and suspension cultures of Rubia cordifolia and to screen the in vitro cultures for synthesis of naphthoquinone and quantify it. It was also envisaged to enhance the level of product synthesis in in vitro cultures and to assess the anticancerous activity of in vitro and in vivo extracts in terms of cytotoxicity, antioxidant and prooxidant activities in vitro. Leaf, nodal and root derived callus cultures of Rubia cordifolia were established in vitro. Explants were pre treated with the fungicide, Bavistin 2.5 per cent for 15 minutes. Surface sterilization with mercuric chloride (HgCl2) at 0.1 per cent for 1 min and 30 sec was effective for yielding healthy, contamination free cultures from nodal segments and leaves, respectively. MS medium at full strength, supplemented with NAA at 2 mg l-1 along with BA at 0.5 mg l-1 was observed ideal for initiation and proliferation of calli. The auxin synergist phloroglucinol, when supplemented to the medium, did not not yield encouraging results, with respect to callusing in the experimental species. Root derived cultures were inferior with respect to callus initiation and proliferation, registering low values for all the parameters studied. Incubating in vitro cultures under illuminated condition at 26 ± 2 C was superior to dark incubation, with respect to callus initiation and proliferation. Chloroform – methanol at 8.5 :1.5 ratio was indentified as the appropriate solvent system for detection of naphthoquinone on thin layer chromatograms in the test extracts of the experimental species, with alcoholic KOH (10 per cent) as the spray reagent. Ms medium at full strength, fortified with NAA and BA at 2.0 mg l-1 and 0.5 mg l-1 respectively, which recorded maximum naphthoquinone synthesis, was standardized as the production medium. Enhancing concentration of sucrose to 5 per cent in the production medium, did not elicit a positive response on naphthoquinone production in vitro. Reducing nitrate concentration of the production medium, to half and one fourth the original concentration, resulted in enhanced in vitro synthesis of the target compound. Supplementing the production medium with yeast extract (1 per cent and 2 per cent) as well as precursor feeding with phenyl alanine and tyrosine each at levels of 50 mg l-1, 100 mg l-1 and 150 mg l-1 exerted a favourable influence on synthesis of naphthoquonines, in vitro. Incubation in dark resulted in marginal increase in in vitro production of naphthoquinones. Incorporation of autoclaved mycelia of Pythium aphanidermeatum at levels of 2.0 per cent and 5.0 per cent resulted in enhanced in vitro production of naphthoquinone. The abiotic elicitor, salicylic acid at concentration of 10 μM and 100 μM resulted in maximum synthesis of naphthoquinones in in vitro root cultures (8.76 units g -1 calli) of Rubia cordifolia. Immobilization of test calli with sodium alginate – calcium chloride complex as well as subjecting the in vitro cultures to stress conditions, as imposed by sorbitol failed to bring about an enhancement in the in vitro production of naphthoquinones. None of the explants employed in the study induced hairy roots, when co- cultured with the Agrobacterium rhizogenes strains, MTCC 2364 and MTCC 532. Based on cell count, subculturing intervals of leafs, nodal and root derived suspension were fixed as 24, 27 and 27 days respectively with the respective packed cell volume as 0.93 per cent, 0.83 per cent and 0.80 per cent. Naphthoquinone was detected, in ex vitro and in vitro test extracts at all levels of maturity tested. Both ex vitro and in vitro root extracts exihibited maximum cytotoxicity, as revealed by the percentage of cell death on DLA and EAC cell lines as well as their IC50 values. As compared to whole plant extract, in vitro systems of the experimental species exhibited least antioxidant action. Extent of pro-oxidant activity was higher in in vitro root extract of the experimental species.