Enhanced Rhinacanthin Production in Rhinacanthus nasutus Roots Using a Hydroponics and Elicitation System

Background: A proficient hydroponic system for the cultivation of Rhinacanthus nasutus has been implemented with the aim of augmenting rhinacanthin production. Elicitation stands out as a viable technique for bolstering the yield of rhinacanthin. Materials and Methods: A hydroponics system of R. nasutus was treated with six elicitors, namely chitosan, Trichoderma harzianum extract, sodium alginate, lawsone, methyl jasmonate, and salicylic acid at three concentrations. A suitable elicitation period for the selected elicitor was also determined. The contents of rhinacanthin-C, -D, and -N accumulated were determined using an HPLC method. Results: Amongst these, chitosan (0.15 mg/mL) and T. harzianum extract (1.0 mg/mL) significantly enhanced rhinacanthin production and gave the highest total rhinacanthin content, up to 6.0-6.1% w/w, which was 2.2-fold higher than the untreated roots (2.7% w/w). In addition, lawsone (3.0 μM) and salicylic acid (100 μM) significantly increased rhinacanthin production up to 4.6% and 3.4% w/w, respectively, while neither methyl jasmonate nor sodium alginate increased rhinacanthin production. The suitable elicitor-contact periods for chitosan, T. harzianum extract, and lawsone were 48, 24, and 72 h, respectively. Moreover, the leaves harvested from these optimized conditions also contained markedly high contents of rhinacanthins, up to 5.4%, 6.7%, and 5.1% w/w, respectively. Conclusion: The present study established the optimized elicitation methods for the R. nasutus hydroponics system using chitosan, T. harzianum extract, and lawsone as elicitors to obtain the high-rhinacanthin-producing roots and leaves. These hydroponics and elicitation systems might be alternative sources of the high-quality R. nasutus roots and leaves.