Physiological and transcriptomic responses of pumpkin to lead and ozone stress

The co-pollution of ozone (O₃) and lead (Pb) poses significant threats to crop growth and human health, thus attracted serious concern. This study examined the individual and combined effects of Pb and O₃ treatment on the growth, photosynthesis, antioxidant enzyme activity, gene expression, and the ascorbate-glutathione (ASA-GSH) cycle in pumpkin seedlings. The results revealed that Pb and O₃ treatments, both individually and in combination, significantly inhibited the growth of pumpkin seedlings, as evidenced by reductions in leaf area, stem diameter, dry weight, and fresh weight. Remarkably, the combined Pb and O₃ treatment exhibited more pronounced negative effects on plant growth than the individual stressor. This phenomenon could be attributed to two key factors. First, the co-exposure of Pb and O₃ disrupted chlorophyll synthesis and reduced the activity of key photosynthetic enzymes (Rubisco and FBPase) by downregulating the expression of photosynthesis-related genes (RCA, RBCS, and FBPase), thereby impairing photosynthesis and hindering pumpkin growth. Second, the combined treatment reduced antioxidant enzyme (SOD, POD, CAT, and GR) activity, disrupted the ASA-GSH cycle, and triggered the malondialdehyde (MDA) accumulation, thus exacerbating oxidative damage. This study provides new insights into the broader impacts of atmospheric and soil pollution on crop health, resilience and safety.