Reduced graphene oxide modulates antioxidant responses and specialized metabolism in the medicinal orchid Dendrobium chrysotoxum: an integrated transcriptomic and metabolomic perspective

Dendrobium chrysotoxum is an important medicinal orchid containing a wide range of bioactive compounds, including alkaloids, flavonoids, terpenoids, and bibenzyls. Despite its pharmacological importance, the physiological and molecular responses of this species to nanomaterial elicitation remain unclear. Reduced graphene oxide (rGO) has emerged as a potential nano-elicitor that can affect plant physiological status, antioxidant regulation, and specialized metabolism. To examine its effects on Dendrobium chrysotoxum , seedlings were grown under greenhouse conditions and exposed to a series of rGO concentrations. Changes in growth-related traits, antioxidant defense, polysaccharide accumulation, total flavonoid content, and transcriptomic and metabolomic profiles were assessed. The responses were strongly concentration- and time-dependent. At 21 d after treatment, 100 mg·L −1 rGO (T3) increased CAT, SOD, and POD activities by 225.2%, 387.8%, and 22.2%, respectively, compared with CK. Polysaccharide and soluble sugar contents were also increased by 206.7% and 35.0%, respectively. Leaf total flavonoid content showed a transient middle-stage increase, with T3 showing a 56.79% increase over CK at 14 d. Although MDA accumulation increased under rGO exposure, the MDA level in T3 at 21 d was 57.4% and 71.3% lower than those in T4 and T5, respectively, indicating lower membrane lipid peroxidation than under high-dose treatments. Multi-omics analysis further detected 1,804 DEGs and 1,005 differential metabolic features with putative annotations, with flavonoid and terpenoid-related metabolism emerging as two major pathways altered by rGO exposure. Within these pathways, candidate genes encoding glycosyltransferases, cytochrome P450s, and sesquiterpene synthases, along with regulatory factors such as DcMYB20 and DcbHLH130, were associated with treatment-related variation in flavonoid and terpenoid metabolism. These results clarify the response pattern of a medicinal orchid to rGO treatment and provide a basis for future studies on nano-elicitation responses and candidate metabolic regulation in Dendrobium .