The wild resource of Dendrobium candidum, a well-known epiphytic orchid, is limited. Plant cell culture technology is a promising alternative for production of high-value secondary metabolites .In this research, factors affecting the induction, maintenance, and multiplication of callus from protocorm-like bodies (PLBs) of D. candidum were systematically studied, and a technical callus inducing system with 100% rate was established which higher than previously reported values. The result showed that 2,4-dichlorophenoxy acetic acid(2,4-D) and 1-naphthalene acetic acid (NAA) could of benefit to the callus induction. The optimized medium for callus induction was MS medium containing 0.5 mg/L 2,4-D and 0.25 NAA or 0.5 mg/L kinetin (KT). The callus clump enrichment method was used for directional screening and cell adaptation on MS medium supplied with plant growth regulators (PGR) such as 5 mg/L NAA and 0.5 mg/L 6-benzyladenine (6-BA) or KT for 30 days per cycle. After 6 to 9 months, D. candidum cell lines were obtained and the histological analysis showed that the main differences between callus and PLBs were meristematic cell content and internal cell differentiation degree, and the meristematic cells distributed in the external strip were contributed to the formation of callus. At last, the amount of polysaccharides and total amino acids were compared between the obtained cell lines, tissue culture seedlings and PLBs. The results showed that polysaccharides was 24.67% in callus and higher than that in tissue culture seedlings and PLBs. The amount of total amino acids was 5.94% in callus and higher than that in tissue culture seedlings. So the callus is considered a good choice for the expanding of D. candidum medicine sources.
Key words: Dendrobium candidum, Callus induction, tissue culture, natural products, plant growth regulators
6-BA, 6-benzyladenine,2,4-D 2,4-dichlorophenoxyacetic acid; Kin, kinetin; MS, Murashige and Skoog (1962) medium; NAA, Naphthaleneacetic acid; PLBs, Protocorm-like bodies; TDZ, thidiazuron; PIC, picloram.
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