Why Do Pumpkins Accumulate Pollutants in Their Edible Flesh?
Knowing what causes the accumulation of pollutants in pumpkins and other gourds could help to make produce safer.
The Cucurbitaceae or gourd family of plants includes many popular fruits and vegetables, such as pumpkins, squash, watermelon, cucumbers and zucchini.
While these plants all make for tasty treats, scientists are aware of another commonality – they tend to take up pollutants from the soil they are planted in, which can accumulate in their edible parts and potentially pose a health risk.
Not all edible plants have this type of accumulation issue, which raises the question: why do gourds do this? With a new study published in the journal Plant Physiology and Biochemistry, scientists are one step closer to the answer.
Extracellular protein secretion could explain pollutant accumulation
Understanding the mechanism behind how these plants accumulate pollutants is crucial if scientists are to help farmers grow safer produce.
“The pollutants don’t easily break down and thus pose a health risk to people who eat the fruit. Interestingly, other plants don’t do this and so I became interested in why this happens in this group specifically,” said study author Hideyuki Inui, an associate professor at Kobe University’s Biosignal Research Center.
In previous research, Inui’s team found that plants in the gourd family contain a class of major latex-like proteins (MLPs) that exhibit a strong binding affinity to hydrophobic organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs).
Polycyclic aromatic hydrocarbons (PAHs)
PAHs are produced when wood, coal and garbage are burned, and as a component of automobile exhaust. Most human exposure to PAHs occurs through smoking or through eating smoked or grilled food.
“However, these proteins exist in many other plants, and even among the gourds, there are varieties that are more prone to accumulating pollutants than others. We then noticed that in the highly accumulating varieties, there are higher concentrations of the protein in the sap,” said Inui.
In the new study, Inui’s team took a closer look at the secretion of these pollutant-transporting proteins into the plant sap. They saw that MLPs in the highly accumulating plants are indeed exported into the sap, whereas other variants are retained in the cells.
The team found that this difference is likely due to a small variation in the MLP’s amino acid sequence. This variation acts as a tag that tells the cell which proteins it should retain and which should be excreted.
“Only secreted proteins can migrate inside the plant and be transported to the aboveground parts. Therefore, this seems to be the distinguishing factor between low-pollution and high-pollution plant varieties,” Inui explained.
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To test this further, the researchers introduced two versions of the MLP into unrelated tobacco plants. The plants that were given the highly accumulating version of the MLP promptly began to excrete the protein into the plant sap, while the plants given the other version continued to hold it intercellularly.
From cleaner produce, to cleaner soil
Through understanding the mechanisms behind these pollutant-transporting proteins, scientists hope they will be able to develop new approaches for growing safer crops that do not accumulate pollutants in their edible flesh, thus reducing human exposure to potentially harmful contaminants.
“By controlling the behavior of contaminant-transporting proteins, through genetic modification of their pollutant-binding ability or its excretion into the plant sap, we believe it will be possible to cultivate safe crops that do not accumulate harmful chemicals in their edible parts,” said Inui.
However, the Kobe University team does not want to stop there. If they can create plants that do not accumulate pollutants, they might also be able to create new gourd varieties that will act as super-accumulators. These plant varieties could then intentionally be planted in polluted soils, where they will draw up the contaminants through their roots, leaving cleaner soil behind.
“I started this research because I was looking for plants that can detect and digest pollutants effectively. Therefore, I also envision that we could use the knowledge gained through this work for creating plants that are more effective in absorbing soil pollutants. This could turn into a technology for cleaning contaminated soils,” Inui said.
Reference: Yoshida M, Suwa M, Eto D, et al. Extracellular secretion of major latex-like proteins related to the accumulation of the hydrophobic pollutants dieldrin and dioxins in Cucurbita pepo. Plant Physiol Biochem. 2025;229:110612. doi: 10.1016/j.plaphy.2025.110612
This article is a rework of a press release issued by Kobe University. Material has been edited for length and content.
