Influence of Exogenous Melatonin and UV-C Exposure on the Biomass Accumulation and Phytochemistry of Alcea rosea Callus Cultures

Abstract

Alcea rosea, commonly known as Hollyhock, is prized for its wide applications as antioxidant, antibacterial, and anticancer agent. Literature states that a number of biotechnological approaches are needed for the viable production of plant biomass and bioactive compounds. Elicitation has established itself as a highly efficient method for enhancing the secondary metabolites production in in-vitro cultures. The current study involved the exposure of callus cultures of Alcea rosea to various treatments of UV-C exposure and melatonin as elicitors. Enhanced biomass accumulation with higher production of phytochemical content were the main goals of this study. UV-C exposure resulted in maximum biomass accumulation (FW: 359.13 g/L, DW: 12.99 g/L) at UV-C exposure of 30 (mins). In contrast, maximum biomass accumulated (FW: 226.43 g/L, DW: 10.20 g/L). This trend was also followed in antioxidant activities with maximum ORAC (960.57 µM TEAC) and CUPRAC (556.23 µM TEAC) at UV-C 30 (mins); only the control showed highest activity for CAA (78.18 % ROS/RNS) which was followed by Callus extract at UV-C 30 (mins) with a percent inhibition (78.08) of CAA assay. The phytochemical profile through HPLC revealed 9 anthocyanins, which are responsible for imparting color to the Alcea rosea nigra flowers. Malvidin 3-O-malonylglucoside was the anthocyanins produced in the highest content. Maximum accumulation of phytochemicals (7.47 µg/g DW) was detected in Alcea rosea callus cultures under melatonin (25 mg/L) stress, which was more than 2 folds increase than the control (7.47 µg/g DW). Melatonin (3 mg/L) showed maximum tyrosinase inhibition (53.18 %) and pentosidine-like AGEs (70.3%). Whereas the maximum elastase inhibition (73.70%) and vesperlysine-like AGEs (36.8%) was exhibited by callus extracts at melatonin (25 mg/L). These higher inhibition percentages suggest role of Alcea rosea extract in alleviating compounds which cause age-related diseases and issues such as hyperpigmentation and elastosis, suggesting it’s potential use in the cosmetics industry. Further study is needed to relate genes involved in the expression and regulation of anthocyanins involved to better incorporate Alcea rosea into the cosmetics industry.