Induction of betacyanin synthesis and pigment accumulation in cell suspension cultures of portulaca

摘要

The establishment of betalain-producing cell suspension cultures in Portulaca is reported for the first time. Addition of ascorbic acid(AsA) and sufficient osmotica to the culture medium was critical to the success. Betacyanin production was best at 1 x 10~3 mg l~-1 AsA. Small cell aggregates, formed in MS-AsA medium supplemented with 150 mM mannitol and 150 mM sorbitol, accumulated the highest relative amounts of betacyanins. The growth rate of cell suspension cultures increased 3-to 4-fold within 14 days in modified MS-AsA medium supplemented with 5 #mu#M 2,4-D. The betalain content of suspended cells increased during the first 2 day in liquid culture, thereafter decreased slightly and increased again during the logarithmic phase of cellular growth. A lower concentration of 2,4-D inhibited the growth of cultures but did not significantly affect betacyanin accumulation. Addition of cytokinin inhibited growth and also resulted in decreased betacyanin accumulation. The pigmentation of cultured cells decolourized upon transfer to dark conditions but was regained in decolourized cells at 12 to 24 hours after light exposure. The levels of endogenous free tyrosine and DOPA, precursors of betalains, decreased in response to light and slightly increased again after 24 hours of light treatment. Betanin, the main pigment component, as well as other betacyanins present, dramatically increased after 24 hours under light conditions in our Portulaca cell suspension culture system.