Researchers from Kobe University have identified a molecular mechanism by which gourds such as pumpkins, squash and zucchini absorb stubborn soil pollutants and concentrate them in their edible parts. The team has discovered that a particular class of proteins acts as a conduit for hydrophobic compounds like dieldrin and dioxins, enabling their movement via plant sap from roots to fruit.
The study revealed that these proteins vary in their amino-acid sequences in different varieties of the gourd family. In high-accumulating plants the proteins are secreted into the sap, while in those that accumulate less pollution the same proteins remain inside cells. According to associate professor Hideyuki Inui, “Only secreted proteins can migrate inside the plant and be transported to the above-ground parts. Therefore, this seems to be the distinguishing factor between low-pollution and high-pollution plant varieties.” This finding was confirmed by inserting the high-accumulation protein into unrelated tobacco plants, which then began exporting it into sap and showed increased pollutant movement.
The implications of this work extend to both food safety and environmental remediation. On the one hand, varieties of gourds that naturally channel pollutants into fruit pose a risk to consumers in areas with contaminated soils. On the other hand, by manipulating these transport proteins through genetic or selective breeding, the researchers believe it is possible to develop cultivars that either minimise pollutant uptake into edible parts or maximise uptake into aerial biomass for use in phytoremediation of polluted land. The research paper published in Plant Physiology and Biochemistry details these findings and underscores the potential to breed “safe crops that do not accumulate harmful chemicals in their edible parts”.
Soil pollutants such as persistent organic pollutants like dieldrin and dioxins are characterised by resistance to degradation and a tendency to accumulate in biological systems. In the gourd family, high accumulation of these compounds in fruit has been observed but until now lacked a clear mechanistic explanation. The Kobe University team pinpointed that the difference arises from the extracellular secretion of major-latex-like proteins that bind these hydrophobic pollutants and move them through plant vascular structures. They attribute the difference between high- and low-accumulation varieties to a small molecular “tag” in the protein that signals whether the cell should release it into the sap or retain it.
Critically, this mechanism does not appear unique to gourds from a phylogenetic standpoint; rather, the protein class is found in many plants. What makes the difference is the secretion behaviour. In practical terms, this means that gourds grown in contaminated soils may act as silent conduits, concentrating toxins where people expect nutritious products. For example, mixing melon or pumpkin fruit with lower-risk vegetables may inadvertently increase exposure to POPs. Agricultural scientist Inui emphasises that awareness of this uptake mechanism is “crucial to creating safer produce.”
Nevertheless, the prospect of turning this mechanism into an advantage has drawn interest. By selecting varieties with reduced secretion of the transport protein, breeders could produce gourds that store fewer pollutants in fruit. Conversely, the same mechanism could be harnessed for phytoremediation: plants could be engineered to become “bio-cleaners,” absorbing pollutants into biomass that is then harvested and disposed of safely. The research team acknowledges that further work is needed on field trials, regulatory pathways, and consumer acceptance of modified crops.