Abstract:
Genus Rheum is known for its abundant and therapeutically important phytoconstituents across traditional medicine systems. Their synthesis and accumulation are highly complex, influenced by environmental factors and developmental genetic circuits. This study aimed to identify and quantify specialized metabolites (SMs), assess the impact of altitude and environmental stress, and evaluate total antioxidant potential in five Rheum species from different ecological niches of the NW Indian Himalayas. Among seven extraction solvents tested by HPLC-ESI-MS/MS, ethyl acetate provided the highest yield and was used for all subsequent extractions. LC-QTOF-MS analyses revealed R. spiciforme as the richest in metabolite content, followed by R. australe, R. tibeticum, R. webbianum, and R. moorcroftianum. Intra-specific chemical variability identified elite chemotypes within species. Altitude positively correlated with metabolite accumulation and enhanced antioxidant components, including photopigments, flavonoids, and phenolics. Higher altitudes were associated with increased oxidative stress, reflected by elevated levels of ascorbate peroxidase, catalase, superoxide dismutase, and proline. Five non-enzymatic assays confirmed R. tibeticum and R. spiciforme as having the highest antioxidant potential. Overall, these findings provide novel insights into the interactions between species, environmental factors, and bioactive metabolite synthesis, enhancing our understanding of plant adaptive responses to diverse stress stimuli.