Physiological and biochemical adaptations of Plectranthus amboinicus under severe cadmium and lead contamination

Pollution from heavy metals, particularly cadmium (Cd) and lead (Pb), poses a significant threat to ecosystem stability and agricultural productivity. This study examines the physiological and biochemical responses of Plectranthus amboinicus under Cd and Pb stress. Growth parameters, pigment content, antioxidant activity, and protein expression were evaluated. At the highest Cd and Pb concentrations (100 mg/kg and 1000 mg/kg, respectively), chlorophyll a decreased by 37.1 % and 33.3 %, while carotenoids increased by 128.8 % and 35 %, indicating protective stress responses. Enzymatic antioxidants including catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) were significantly upregulated. Non-enzymatic antioxidants also rose sharply, with ascorbic acid levels increasing by 326.4 % under Cd and 449.9 % under Pb stress. Metal accumulation was higher in roots than shoots, reflecting an adaptive root-retention strategy. Proteomic analysis further confirmed stress-induced changes in protein expression. These findings enhance understanding of how P. amboinicus responds to heavy metal toxicity and may support future studies on plant tolerance mechanisms in contaminated environments.