Reduction in heavy metal Cd accumulation by exogenous proline in Alternanthera philoxeroides

A perennial herb from the Amaranthaceae family, Alternanthera philoxeroides is a hyperaccumulator of the heavy metal cadmium (Cd). It possesses high medicinal value and demonstrates exceptional resistance. As such, it stands as a promising candidate for the remediation of cadmium-contaminated soil. To investigate the effects of heavy metal cadmium (Cd) on the morphology, physiological index, and antioxidant system of A. philoxeroides, we conducted a series of physiological and biochemical experiments using this plant species within the same watershed with proline added exogenously. This study aimed to unravel the mechanisms by which externally applied proline influences A. philoxeroides under Cd toxicity. The results revealed that Cd inhibits A. philoxeroides roots, stems, and leaves. However, when external proline was applied, it mitigated the damage caused by Cd, alleviating the toxic effects of Cd on A. philoxeroides. Concerning physiological indices, the levels of malondialdehyde (MDA), hydrogen peroxide (H₂O₂), free proline (Pro), and soluble sugar (SS) of A. philoxeroides were significantly increased under Cd-induced toxicity. Meanwhile, there were no significant differences in soluble protein (SP) levels among treatments. Regarding antioxidant system indices, Cd toxicity significantly increased the contents of Glutathione peroxidase (GPX), peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) contents were significantly increased by in A. philoxeroides. but the differences were not significant between treatments for SOD contents in the stem. In summary, the addition of exogenous proline to A. philoxeroides proved effective in mitigating the toxic effects of Cd. In order to provide a scientific theoretical basis and reference basis for the future development and utilization of A. philoxeroides in the remediation of Cd-contaminated soil.