Dose-dependent inhibition of photosynthesis and redox alterations in cymbopogon nardus exposed to cadmium and chromium: evidence through the activity of RUBISCO.

Abstract

This study comprehensively assessed the physiological adaptations of Cymbopogon nardus (citronella) exposed to varying concentrations (25-100 mg.kg^-1) of cadmium (Cd) and chromium (Cr). The phytoremediation potential was also evaluated over a 60d greenhouse experiment with triplicate replication, where Cd and Cr were introduced as cadmium chloride (CdCl₂) and potassium dichromate (K₂Cr₂O₇), respectively. While elevated metal concentrations adversely affected plant growth and chlorophyll content, C. nardus exhibited remarkable tolerance. This was evidenced by the upregulation of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidise (APX), alongside increases in reduced glutathione (GSH) and proline, effectively mitigating oxidative stress. However, high-intensity metal exposure eventually overwhelmed these systems, leading to reactive oxygen species (ROS) accumulation and oxidative damage. Notably, Western blot analysis revealed that Cr distinctly induced a greater reduction in ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity compared to Cd, highlighting nuanced physiological responses to different metals. The plant demonstrated substantial phytoremediation capacity, achieving bio-concentration factors (BCF) of 0.25 for Cd and 0.28 for Cr at 100 mg.kg^-1, and effectively removing 75.1% of Cd and 72.1% of Cr from contaminated soil. The novelty of this study lies in its comprehensive analysis of physiological adaptations and phytoremediation capabilities of C. nardus under both Cd and Cr stress, revealing its potential as a robust phytoremediator. The observed differential impact on Rubisco activity and efficient metal removal capacity underscore the plant's suitability for remediating soils contaminated with these prevalent heavy metals.