Phenylethanoids, phenylpropanoids, and phenolic acids quantification vis-a-vis gene expression profiling in leaf and root derived callus lines of Rhodiola imbricata (Edgew.)

Salidroside and rosavins have been found as the most potent ingredients used in Rhodiola based herbal formulations. Rhodiola imbricata is a medicinal herb of the trans-Himalayan Ladakh region of India. Since, the natural supply of this herb is rapidly decreasing, due to its over-exploitation, high altitude region, and traditional usage in the Amchi system of medicine. In the present study, friable callus culture was developed for the first time from leaf and root explants of R. imbricata. Furthermore, callus cell lines were also evaluated for rapid growth rate and high metabolite accumulation. The results revealed that callus induction frequency observed in juvenile leaves (100 %) and roots (87.50 %) in MS medium enriched with 0.5 mg/L TDZ and 1 mg/L NAA. Scanning electron microscopy (SEM) analysis was done for histological observations of the callus surface. A selective and efficient ultra-performance liquid chromatography with PDA detector (UPLC-PDA) method was developed and validated for the quantification of phenylethanoids, phenylpropanoids, and phenolic acids. The maximum salidroside was detected in leaf derived friable green calli (3.59 mg/g DW) subsequently followed by leaf derived friable white calli (2.31 mg/g DW). While rosavin and rosarin were detected maximum in root derived compact green calli (0.15 mg/g DW) and root derived friable green calli (0.07 mg/g DW). Genes encoding enzymes involved in salidroside and rosavins biosynthesis were also investigated for transcript abundance in wild as well as in vitro cultures using the RT-qPCR approach. The present study explained the friable callus culture as a potential alternative approach to obtain higher metabolite yield in R. imbricata. Further, it can be used for sequential scale-up of metabolite at bioreactor level to meet the industrial demand.