Naphthalene Acetic Acid as a Potent Elicitor of Coordinated Defense Responses and Terpenoid Metabolism Reprogramming in the Medicinal Succulent Euphorbia trigona Mill. (Euphorbiaceae)

Plant growth regulators (PGRs) are effective tools for enhancing phytochemical production in medicinal plants. This study investigated the elicitation efficacy of gibberellin (GA3) and auxins (IAA, IBA, NAA) at 250 mg/L on the medicinal succulent Euphorbia trigona Mill. (Euphorbiaceae). After seven months, NAA treatment significantly increased root biomass and uniquely triggered a coordinated defense response. This was evidenced by the significant upregulation of phenylalanine ammonia-lyase (PAL) and increased activities of the antioxidant enzymes peroxidase and superoxide dismutase. Consequently, NAA induced a substantial accumulation of defense-related metabolites, most strikingly a five-fold increase in terpenoids, along with elevated flavonoids and flavonols. GC-MS profiling suggested an NAA-induced reprogramming of the terpenoid profile. The results demonstrate that unlike GA3 or other auxins, NAA is the most effective elicitor for enhancing bioactive compounds in E. trigona through a coordinated defense network.