Integrated ultrastructural, physiological and transcriptomic analyses uncover alterations in photosynthetic biomacromolecule structures by cadmium and cerium co-exposure and their regulation by hormone signaling and antioxidant pathways in maize

Co-contamination of soil by cadmium (Cd) and cerium (Ce) has become increasingly prevalent and poses a significant threat to agricultural productivity. To investigate the effects of this joint pollution on plant growth, we investigated the ultrastructural, transcriptomic, and molecular responses of maize seedlings to Cd, Ce, and their mixtures. The results indicated that Cd, Ce, and their mixtures had detrimental effects on maize growth by reducing biomass accumulation (shoot dry weight was decreased by 59.94 %, 37.94 %, and 54.10 %, respectively), disrupting photosynthesis and chlorophyll synthesis, and causing ROS imbalance. However, co-exposure to Cd and Ce resulted in a less severe impact on the maize photosynthetic system compared to Cd treatment alone, as it reduced the production of osmiophilic plastoglobuli. Transcriptomic and molecular docking analyses revealed that Ce enhanced the repair of photosystem II under Cd stress by upregulating chlorophyll-binding proteins and carbon assimilation proteins. SOT5 (Zm00001eb327110) is primarily involved in photosynthesis, ROS scavenging, and phytohormone signaling, which could be crucial for breeding stress-resilient crops. For the first time, we demonstrate that Cd and Ce interacted antagonistically in transcriptomic level. This study provides new insights into how maize responds to heavy metals and rare earth elements and highlights critical pathways for improving stress tolerance.