Presence, in the Rhizosphere and Leaf Extracts of Zucchini (Cucurbita pepo L.) and Melon (Cucumis melo L.), of Molecules Capable of Increasing the Apparent Aqueous Solubility of Hydrophobic Pollutants

In the wake of the observation made by Hulster and Neumann that zucchini absorbs large quantities of dioxins and furans through its roots, our research is aimed at contributing to the description of the mechanism involved. According to the current hypothesis, a molecule produced by the plant and released into its root exudates binds to the pollutant. These complexes are more hydrophilic than the pollutant itself. These are more mobile in the soil solution, are absorbed by the roots, and translocated into all plant parts. We first attempted to isolate a molecule that is capable of binding 2,3,7,8-TCDD in Cucurbita pepo L., Cucurbita maxima Duchesne ex Poiret, Cucumis sativus L., Cucumis melo L., Daucus carota L. and Lycopersicon esculentum L. These trials showed that such a molecule is present in the tissues and the rhizosphere of melon. Therefore, we focused our research on this species, using zucchini as a reference. Later tests on solubility and precipitation characteristics showed that the binding molecules found in both species had identical properties in many respects. It appears that zucchini and melon contain several binding molecules, and results suggest that at least one of these would be of a proteinic nature. A fundamental study of the binding substance could lead to applications in the fields of soil remediation by phytoextraction.