Variability in cadmium stress tolerance among four maize genotypes: Impacts on plant physiology, root morphology, and chloroplast microstructure

Cadmium (Cd) is detrimental to both plants and humans. Maize (Zea mays L.) genotypes exhibit variations in Cd accumulations. This study examined variations in Cd accumulation and tolerance among four maize genotypes with contrasting root morphology. The four maize genotypes were cultivated in a semi-hydroponic system with three Cd concentrations (0, 10, 20 mu mol L-1). The effects of Cd on plant growth and physiology were assessed 39 days after transplanting. Results showed that root characteristics were positively correlated with root Cd accu-mulation and the bioconcentration factor under Cd20 treatment. Genotypes Shengrui999 and Zhengdan958 exhibited higher total Cd content than Xundan29 and Zhongke11 under Cd20 conditions. Cd toxicity led to membrane degradation of chloroplast mesophyll cells, loosening and swelling of grana lamella, and reduced starch reserves. The greater tolerance of Shengrui999 and Zhengdan958 was contributed to factors such as root biomass, shallower root depth, higher Cd content, accumulation of osmolyte such as soluble protein, antioxidant activities such as catalase (CAT), and the presence of phytohormone gibberellic acid. The study establishes a link between root morphology, Cd accumulation, and tolerance in maize plants, as demonstrated by the higher Cd accumulation and shallower root system in Cd-tolerant genotypes. This research provides a foundation for breeding maize cultivars better suited for adaptation to moderate Cd-contaminated environments.