Precursor- induced bioaccumulation of secondary metabolites and antioxidant activity in suspension cultures of Dendrobium fimbriatum, an orchid of therapeutic importance

Orchids are important sources of various bioactive molecules of medicinal importance. Dendrobium fimbriatum figures prominently among the various medicinal orchids used on a global scale in herbal preparations. It is an important constituent of the “Herba Dendrobii” and is widely used in Traditional Chinese Medicine (TCM). Being a highly valued herb facing the risk of extinction, use of precursors in cell suspension cultures offers valuable alternative to cater to its large-scale demand. The present research focuses on a wide scale application of various precursor molecules to upscale the production of secondary metabolites under controlled in vitro conditions so as to minimize the pressures exerted on its natural populations for collection. The cultures of D. fimbriatum inoculated with caffeic acid (CA) in the medium exhibited the highest amount of total phenolic content (50.73 mg GAE/gm DW at 0.5 mM CA) and flavonoid content (5.73 mg QE/gm DW at 1.0 mM CA). However, highest amount of tannin content (14.77 mg TAE/gm DW) was recorded in the cultures treated with p-coumaric acid at 4.0 mM in the medium. Also, cultures treated with ferulic acid at 2.0 mM in the medium resulted in the accumulation of a higher content of total alkaloids (317.82 mg ATP/gm DW). Simultaneously, the antioxidant activity of the precursor - treated cultures of D. fimbriatum measured by DPPH and FRAP assay revealed that the antioxidant activity was highest in the cultures treated with 0.5 mM caffeic acid which could be attributed to the increased production of total phenolic contents. The present research is significant as it reveals baseline information which if exploited scientifically can cater to an enhanced regular supply of secondary metabolites throughout the year by the use of precursors in the cultures without affecting the natural orchid populations, wherein Dendrobium fimbriatum is used as a model plant taxon.