Scientists Finally Discover Why Pumpkins Absorb Pollution

The proteins help transport toxins through the plant’s sap. By modifying this process, researchers hope to grow vegetables that resist contamination—or use plants to cleanse toxic soils. The finding could make future harvests both safer and more sustainable, the journal Plant Physiology and Biochemistry reported.

Plants in the gourd family, which includes pumpkins, zucchini, cucumbers, and melons, have an unusual tendency to take up pollutants from the soil and store them in their edible parts. Kobe University agricultural scientist Hideyuki Inui explains, “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.”

In earlier studies, Inui and his team identified a group of proteins found in gourds that bind to pollutants, allowing them to move through the plant. Earlier this year, they reported that both the shape of these proteins and how tightly they attach to pollutants determine how much contamination reaches the aboveground portions of the plant.

“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,” says Inui. This observation led the researchers to focus on how the pollutant-binding proteins are secreted into the plant sap.

In a new paper, the Kobe University group demonstrated that in plants prone to high pollutant accumulation, the protein variants are released into the sap, while other forms of the protein stay inside the cells. They found that a tiny difference in the protein’s amino acid sequence acts like a signal tag, directing the cell to either retain or release it.

To confirm this mechanism, the researchers introduced the high-accumulation protein variants into tobacco plants, which then also exported the protein into their sap. “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 explains.

Understanding how pollutants are transported inside plants could help scientists breed safer crops. “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,” says Inui.

Inui also hopes this research can contribute to environmental cleanup. “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,” he says.

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