Tricky treats: Why pumpkins accumulate pollutants

Pumpkins, squash, zucchini and their relatives accumulate soil pollutants in their edible parts. A Kobe University team has now identified the cause, making it possible to both make the produce safer and create plants that clean contaminated soil.

The gourd family of plants comprising pumpkins, zucchini, melons, cucumbers and more are known to accumulate high levels of pollutants in their edible parts. Kobe University agricultural scientist INUI Hideyuki says: “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 previous studies, the Kobe University researcher and his team identified a class of proteins from across the gourd family that bind to the pollutants, thus enabling them to be transported through the plant. Earlier this year they published that the shape of the proteins and their binding affinity to the pollutants influence the accumulation in the aboveground plant parts. “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. Thus, his team turned their attention to the secretion of the pollutant-transporting protein into the plant sap.

In the journal Plant Physiology and Biochemistry, the Kobe University team now publish that they could show that the protein variants from the highly accumulating plants are indeed exported into the sap, whereas other variants are retained in the cells. They could also pinpoint that this is likely due to a small difference in the protein’s amino acid sequence that acts as a tag that tells the cell which proteins to retain within. The team proved their point by showing that unrelated tobacco plants in which they introduced the highly accumulating protein versions also exported the protein into the plant sap. Inui explains: “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.”

Understanding the mechanism behind pollutant accumulation is crucial to creating safer produce. “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.

But the Kobe University researcher has a broader vision. He explains: “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.”

This research was funded by the Japan Society for the Promotion of Science (grant 23241028) and the Murao Educational Foundation.

Kobe University is a national university with roots dating back to the Kobe Higher Commercial School founded in 1902. It is now one of Japan’s leading comprehensive research universities with over 16,000 students and over 1,700 faculty in 11 faculties and schools and 15 graduate schools. Combining the social and natural sciences to cultivate leaders with an interdisciplinary perspective, Kobe University creates knowledge and fosters innovation to address society’s challenges.