The thesis was divided into parts; first part consisted of plant cell and tissue culture studies, while second part constituted biotransformation studies using Labiates cell culture and genetic modification effect on biotransformed products. PART A In first part, in vitro protocol for direct regeneration of Lamiaceae plants were established for biotransformation and other modification studies. For this, three Labiates (Ocimum basilicum, Ocimum sanctum and Agastache anisata) were studied. In O. basilicum, the best response for direct plant regeneration was observed in Murashige and Skoog (MS) culture medium containing IAA 0.025 mg/L + BAP 0.1 mg/L, producing 16.4 shoots having a shoot length of 5.33 cm, and 6.86 roots having a root length of 5.36 cm. The plants were best acclimated in sand: farm yard manure (50:50 w/w) and sand (100 %). In O. sanctum, direct plant regeneration was observed in MS medium containing IAA 0.025 mg/L + BAP 0.1 mg/L, producing 12.4 shoots with a shoot length of 5.94 cm, and inducing 15.0 roots having a root length of 6.05 cm. The plants were best acclimated in sand: farm yard manure (50:50) and sand (100 %). Till date, this is the first report of in vitro propagation of O. basilicum using nodal segment as explants. In Agastache anisata, plant regeneration was observed in MS medium containing IAA 0.05 mg/L + BAP 0.1 mg/L, producing 7.93 shoots with a shoot length of 6.0 cm, and inducing 5.96 roots having a root length of 4.01 cm. The plants were best acclimated in sand: farm yard manure (50:50) and sand (100 %). Till date, this is the first report of in vitro propagation of A. anisata using tissue culture technology. The plant was tested for its bioactivity, and it exhibited potent cytotoxic activity. In order to establish and optimize callus induction protocol, required for the biotransformational studies, different combinations of plant growth regulators (PGR) with MS medium were tested. Out of 60 different combinations, best combination for O. sanctum was DN6 (MS + NAA 2 mg/L + 2,4- D 0.25 mg/L) that produced friable callus. When this callus was transferred into the liquid medium, it started dispersing easily making good suspension culture for biotransformation studies. In O. basilicum, yellow friable granular callus was induced in DN9 (MS + NAA 2 mg/L + 2,4-D 0.5 mg/L), and this was further used for the establishment of cell suspension culture for the biotransformational studies. PART B For the biotransformational studies, six substrates were used in which five were terpenes and one steroid. In total, fifteen compounds were isolated for the first time via this route (plants), but twelve (2, 3, 6, 8-11, 13, 16, 18, 19 and 21) are known and three are new (4, 5 and 14) metabolites. Known compounds were mostly synthetically produced compounds or/and some of them bioconverted from fungus but not through plant cell suspension cultures. These compounds have not been acquired this way by any plant cell culture. In order to seek different derivatives of a given compound; various cell suspension cultures were used against several kind of compounds to get more valuable metabolites. In this connection, podocarpic acid (1) was subjected to biotransformation process employing cell suspension culture of Ocimum species. Both cell culture (Ocimum) and substrate (1) were used for the first with each other. Biotransformation of podocarpic acid (1) by cell suspension culture of Ocimum yielded compounds Methyl podocarpate (2), Podocarpic acid acetate (3), 6α, 7α-epoxy podocarpic acid (4), 6β, 7β-epoxy podocarpic acid (5) and 7-keto podocarpic acid (6). Metabolites 4 and 5 were found to be new metabolites, as deduced on the basis of spectroscopic techniques. Ethynodiol diacetate (7), a steroidal compound has not previously been used for the biotransformation employing the cell suspension culture of Ocimum basilicum. Biotransformation of ethynodiol diacetate (6) by culture of Ocimum basilicum yielded compounds 8-11. 17α-Ethynyl-17β- acetoxyestr-4-en-3-one (8), 17α-Ethynyl-17β-hydroxyestr-4-en-3-one (9), 17α-Ethynyl-3β-hydroxy- 17β-acetoxyestr-4-ene (10) and 17α-Ethynyl-5α,17β-dihydroxyestr-3-ene (11). When totarol (12) was incubated with the cell suspension culture of O. sanctum for 20 days, two metabolites totarol acetate (13) and 6-dehydrototarol (14) were obtained. The metabolite 14 was found to be new as deduced on the basis of spectroscopic techniques. This compound (12) has not been used before for the biotransformation using the plant cultures. It was observed that when artesunate (15) was incubated with O. sanctum cell suspension culture for 10 days, it produced metabolite artemisinin (16). When Sclareol (17, diterpene) was incubated with rapidly growing cell suspension cultures of O. sanctum, it afforded two known compounds 3-keto sclareol (18) and 3β, 3-hyrdroxy sclareol (19), but this is a new route for these biotransformed products. When humulene (sesquiterpene) was incubated with rapidly growing cell suspension cultures of O. basilicum, it afforded a known compound 2,6-diepoxy humulene (22), but this is a new route for this biotransformed product. Bioassay studies were also performed for transformed products obtained through biotransformation. The activities employed were anticancer, antioxidant and enzyme inhibition studies. Transformed compounds did not exhibit any remarkable activity as compared to substrates. To evaluate the diversity of plant cell cultures for biotranformation studies, protoplast isolation and fusion method was tested. For protoplast isolation, in vitro developed leaves and callus of O. sanctum and O. basilicum were used as source tissue. The crucial factors were yield (per ml) and viability of protoplasts for successful protoplast isolation. So, at the optimized enzyme concentration of 0.5 % each of Cellulase R-10 and Macerozyme R-10, the 12 hour incubation is sufficient for optimum protoplast yield (5 x 105 cells/ml) and viability (85%). These isolated protoplasts were then cultured on BH3 + KL medium containing 2,4-D (0.5 mg/L) and NAA (2 mg/L). The further subculturing initially on solid MS medium supplemented with 2,4-D with Kinetin for four weeks, and then BAP 0.1 mg/L and IAA 0.05 mg/L for four more weeks resulted in plantlet formation in O. sanctum only. O. basilicum protoplast did not regenerate into plantlet. The fusion of Ocimum spp. was also performed using PEG and electrofusion method. In electrofusion, the protoplasts of Ocimums did fuse to become a putative hybrid, but they did not survive in culture medium after two weeks of culture. As for PEG fusion method, protoplast did not successfully hybridize and eventually died. The hairy root culture was then established to evaluate their potential for biotransformation and comparison studies were conducted. Hairy root culture was developed by co-cultivating Agastache anisata leaf and stem with root inducing bacterium, Agrobacterium rhizogenes. The induced hairy roots and normal roots were cultured in liquid medium and compound (17) was incubated that yielded biotransformed product (19). However, hairy root culture produce high yield (almost twice) and utilized the substrate (17) completely in 20 days as compared to normal root suspension culture. Finally, tomato (Lycopersicon esculantum) transgenic (expressing Hepatitis B surface antigen) and non-transgenic callus, and suspension culture were employed for biotransformation for comparison studies. Both cultures transformed the substrate (17) yielding metabolite 19. There was no significant difference in biotransformation ability.