The Response of Achyranthes bidentata Blume to Short-Term UV-B Exposure

Ultraviolet-B radiation (UV-B) can boost the accumulation of terpenoids in plants. Here, Ach-yranthes bidentata Blume plantlets were exposed to UV-B radiation for different durations (1, 2, 3 and 4 h) to understand its effect on the accumulation of the medicinally important secondary metabolites oleanolic acid and ecdysterone. Our results showed that UV-B radiation led to reduced chlorophyll a, chlorophyll b and carotenoid production. Additionally, enzymatic antioxidants accumulated in the plant to detoxify ROS under UV-B radiation. Nine known enzyme-encoding genes (HMGS, HMGR, PMK, FPS, SS, SE, GGPPS, β-AS and CAS) involved in secondary metabolism in A. bidentata were analyzed at the transcriptional levels post-UV-B treatment from 0 to 4 h. RT-qPCR analysis revealed an upregulation in the HMGS, HMGR, PMK, FPS, SS, SE, β-AS and CAS genes that are related to the production of oleanolic acid and ecdysterone. We observed a significant increase in oleanolic acid and ecdysterone content at 3 and 2 h UV-B radiation exposure, respectively. The present work provides evidence that UV-B radiation in mild doses can enhance the concentration of these secondary metabolites by upregulating the relative expression levels of key enzyme genes involved in oleanolic acid and ecdysterone biosynthesis. This study provides evidence that short-term UV-B treatments can increase A. bidentata secondary metabolite content and may be a safe approach for generating high oleanolic acid and ecdysterone producing plantlets.