Cistus monspeliensis extract as a prospective biostimulant in enhancing tolerance to cadmium in sorghum plant

Sorghum bicolor (sorghum) is a species known for accumulating high quantities of cadmium (Cd), which can damage physiological and metabolic functions, impede growth, and reduce yield. Maintaining sorghum’s production, therefore, requires enhancing its tolerance to the toxic effects of Cd. In this study, we investigate the effects of Cistus monspeliensis extract (CME) on Cd stress tolerance in sorghum. Sorghum plants exposed to Cd (200 μM) showed a decrease in their growth, biomass, and chlorophyll content compared to unstressed ones. However, CME supplementation (5 mg/l, 20 mg/l, and 60 mg/l) to the stressed plants reversed the detrimental effect of Cd and elevated biomass and pigment content. CME also reduced superoxide ions (O 2 − ) accumulation and boosted the activities of antioxidant system-related enzymes: superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione-S-transferase (GST). Moreover, through examining several carbon–nitrogen enzyme activities (phosphoenolpyruvate carboxylase (PEPC), malate dehydrogenase (NAD-MDH), glutamine synthase (GS), glutamate dehydrogenase (GDH), and aspartate aminotransferase (AAT)), we discovered that CME supplementation modulated the perturbations of carbon and nitrogen metabolism in sorghum plants under Cd stress. CME, therefore, appears to improve Cd stress tolerance by upregulating antioxidant defense enzymes, decreasing ROS production, and improving carbon metabolism and nitrogen assimilation, thus leading to a better growth rate. CME’s Cd stress alleviation effect was generally more prominent at 5 mg/L and 20 mg/L. Graphical Abstract