How cadmium and copper affect pumpkin seed development and energy use

Greg Howard
1st February, 2026

How cadmium and copper affect pumpkin seed development and energy use

Cadmium and copper exposure caused visible stunting and reduced biomass in Cucurbita pepo seedlings, with cadmium producing more severe growth inhibition consistent with its greater disruption of reserve mobilization and seedling establishment.

Image adapted from: Acila et al. / CC BY (Source)

Key Findings

  • In zucchini seeds, cadmium and copper contamination at higher levels (200 µM) disrupted early growth stages, though germination rates were not significantly affected
  • Cadmium was more toxic than copper, significantly reducing seedling length and weight by over 60% compared to copper’s 40% reduction
  • Heavy metals, especially cadmium, hindered the breakdown of stored seed sugars, effectively limiting energy access for the seedlings
Heavy metal contamination in soil is a growing problem for agriculture worldwide, reducing crop yields and potentially introducing harmful substances into the food chain. Cadmium (Cd) and copper (Cu) are two particularly problematic heavy metals, as they are commonly found in polluted areas and can be readily absorbed by plants. A recent study by researchers at University of El Oued and Graphic Era University[1] investigated how these metals affect the very first stages of plant life – seed germination and seedling development – in summer squash (Cucurbita pepo). The research focused on the period of germination, examining what happens when seeds are exposed to different concentrations of Cd and Cu (100–200 µM). Surprisingly, the germination rate – the percentage of seeds that successfully sprout – wasn’t significantly affected by either metal. However, this doesn’t mean the metals were harmless; the study found substantial impacts on the vigour of the seedlings, meaning their overall strength and ability to grow. Seed vigour indices, which combine measurements like seedling length and weight, were significantly reduced. The findings revealed that Cd was more toxic than Cu. Cadmium at 200 µM reduced total seedling length by over 63%, while Cu primarily affected the accumulation of biomass, reducing the seedling weight-based vigour index by around 40%. This difference in toxicity aligns with observations in other plant species, where Cd is generally considered more harmful to plant growth than Cu[2]. A key aspect of the study was examining how the metals disrupted plant development at a biochemical level. Seedlings rely on stored reserves – sugars and proteins – to fuel their initial growth. The researchers found that Cd exposure decreased soluble sugars in the cotyledons (the seed leaves) by 16%, while protein content remained stable, even slightly increased. This suggests Cd hinders the breakdown of proteins for energy, effectively starving the seedling by preventing it from accessing its own food stores. In contrast, Cu at lower concentrations (100 µM) actually increased sugar levels in the cotyledons, indicating a more complex role for Cu, potentially acting as a micronutrient at lower doses. These findings build on earlier research demonstrating that both Cu and Zn, while essential for plant growth, can be toxic at higher concentrations[2]. That study showed that excess Cu disrupts various metabolic processes, leading to reduced growth and yield in summer squash. The current study expands on this by pinpointing a specific mechanism – the disruption of reserve mobilization – that contributes to Cd toxicity. To further understand the overall impact of the metals, the researchers used a technique called principal component analysis. This method identifies the main factors driving differences between the treatment groups. The analysis confirmed that Cd had a much greater effect on metabolic disruption, explaining nearly 80% of the variation observed. This reinforces the conclusion that Cd is the more potent inhibitor of seedling establishment. Interestingly, the effects of Cu are concentration-dependent. The study showed that while higher concentrations of Cu were detrimental, lower levels might even be beneficial, potentially due to Cu’s role as an essential micronutrient. This is consistent with findings in cucumber plants, where low doses of Cu still induced metabolic changes, even without visible effects on growth[3]. The research also highlights the importance of considering the combined effects of multiple stressors. While this study focused on Cd and Cu individually, it's common for plants to be exposed to a mixture of heavy metals in contaminated environments. Previous research on Gyanura procumbens showed that combining Cd and Cu can exacerbate toxicity, reducing growth, metabolite production, and even the medicinal properties of the plant[4]. This suggests that the interaction between different metals can be more harmful than exposure to a single metal alone. The findings from the University of El Oued and Graphic Era University research provide crucial insights into the phytotoxicity mechanisms of heavy metals, particularly Cd and Cu. By understanding how these metals disrupt nutrient mobilization pathways, researchers can develop strategies to enhance crop resilience in contaminated environments.

AgricultureEnvironmentPlant Science

References

Main Study

1) Physiological responses of Cucurbita pepo seeds to cadmium and copper stress: Differential impacts on reserve mobilization, metabolic efficiency, and growth

Published 30th January, 2026

https://doi.org/10.1371/journal.pone.0341814

Related Studies

2) Zinc Application Mitigates Copper Toxicity by Regulating Cu Uptake, Activity of Antioxidant Enzymes, and Improving Physiological Characteristics in Summer Squash.

https://doi.org/10.3390/antiox11091688

3) Metabolomics Reveals the Molecular Mechanisms of Copper Induced Cucumber Leaf ( Cucumis sativus) Senescence.

https://doi.org/10.1021/acs.est.8b00742

4) Effect of Cadmium and Copper Exposure on Growth, Secondary Metabolites and Antioxidant Activity in the Medicinal Plant Sambung Nyawa (Gynura procumbens (Lour.) Merr).

https://doi.org/10.3390/molecules22101623


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