Identifying phytoremediation potential of ten tobacco varieties: Cadmium-induced hormesis, bioaccumulation and...

Cadmium (Cd) is a worldwide emerging pollutant that affects crop production and environmental safety. Tobacco, a strong Cd-hyperaccumulator, has significant economic value in China. Tobacco varieties cultivated in Shaanxi Province have not yet been documented for their Cd tolerance and sensitivity. In this study, we evaluated the morphophysiological responses of ten tobacco varieties under Cd stress (10 mg kg^-1). Among the tested varieties, group-1 (G1) varieties exhibited the Cd-induced hormesis phenomenon with enhancement in morphophysiological development. In contrast, group-2 (G2) and group-3 (G3) varieties showed significant inhibition of 6-49%, 12-42%, and 5-34% in growth, chlorophyll content, and photosynthetic efficiency, respectively. Meanwhile, ROS visualization and quantification confirmed the H₂O₂ and O₂^•‒ accumulation in all tested varieties. This upsurge in oxidative stress caused by Cd accumulation, as CX2-2022 from G3-varieties showed the maximum (13.01) Cd bioaccumulation factor (BAF), while G1-varieties showed lowest values of 5 to 7 for BAF and the highest (2.38) for translocation factor (TF). Moreover, transmission electron microscopic analysis of G2 and G3 varieties showed fewer plastoglobules, starch granules, chloroplasts, and mitochondria, as well as massive black dense Cd-inclusions over the entire cell, while G1-varieties showed Cd mainly in the cell wall and vacuole. Based on morphophysiological responses, Cd BAF, and TF, we identified G1 (Haiyan201, QX106, and QX200) as Cd-tolerant, G2 (Chuanxue3, Haiyan204, and QX110) as moderately-sensitive, and G3 (Haiyan302, QX104, QX100, and CX2-2022) as highly-sensitive varieties. These findings provide valuable insights for the establishment of Cd-tolerance breeding, and maintaining sustainable cultivation in Cd-contaminated soils.