Silver nanoparticles mitigated cadmium toxicity in tobacco by modulating biochemical, cellular and genetic responses

Abstract

Cadmium (Cd) contamination in soil poses hazardous impact on tobacco growth. The present study investigated the role of soil applied silver nanoparticles (Ag-NPs) to reduce Cd stress in tobacco by exploring morphological traits, photosynthetic efficiency, ROS (H₂O₂, O₂^·−) level, antioxidants as defense markers, cell death/viability, cellular and subcellular structural changes, and real-time qRT-PCR based gene expression analysis. The treatments comprised of a control (CK), 20 mg kg^-1 cadmium stress (Cd), 50 µM amino silver nanoparticles (Ag-NPs) suspension, and combined cadmium and silver nanoparticles application (Cd + Ag-NPs). Results indicated that tobacco leaves recorded the maximum Cd content (144.53 µg g^-1), followed by stem (70.96 µg g^-1) and then root (50.15 µg g^-1). The SEM and TEM analyses indicated Cd-induced stomatal injury and massive damage at subcellular level. Confocal microscopic visualization clarified the ROS accumulation and cell death by Cd-mediated redox imbalance. However, application of Ag-NPs effectively reduced Cd bioaccumulation (BCF) and root-to-shoot Cd translocation (TF) rate. Moreover, the Ag-NPs application (Cd + Ag-NPs) mitigated Cd-induced oxidative damage by improving the activities/levels of antioxidants such as APX, AsA, and SOD by 248.45%, 132.67% and 29.43%, respectively, compared with Cd only. The Ag-NPs also upregulated the expression of genes related to growth, chlorophyll, carotenoid biosynthesis, and antioxidative defense. Therefore, Ag-NPs can be employed as a sustainable approach to reduce environmental toxic impact of Cd and also to ensure food safety.