Identifizierung PCDD/PCDF-Mobilisierender Verbindungen in Wurzelexsudaten von Zucchini

Abstract

High affinity to the soil organic matter and extreme hydrophobicity (log Ko/w > 4) are the main physicochemical characteristics of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) limiting their mobility in soils, and the translocation within plants. As an exception, uptake of PCDD/PCDF via the roots and subsequent translocation to the shoots was demonstrated for zucchini (Cucurbita pepo L.). Root exudates of zucchini are able to mobilize PCDD/PCDF from contaminated soils. Probably, certain compounds in the root exudates attach to PCDD/PCDF, forming polar adducts, thus facilating root uptake as well as transport within the plant of the per se extremely hydrophobic PCDD/PCDF. A chemical characterization of these compounds was achieved by differential fractionation of root exudates, xylem sap and plant extracts, using 14C-tetrachlorodibenzo-p-dioxin (TCDD) as a probe to detect the PCDD/PCDF-binding fractions. Insolubility in methanol and in dilute trichloroacetic acid (TCA) as well as UV absorption at 280 nm suggest that PCDD/PCDF binding compounds in root exudates of zucchini are polypeptides. Corresponding electrophoretic polypeptide patterns in the TCDD-binding fractions of root exudates and xylem sap separated by gel permeation chromatography, suggest that roots of zucchini release TCDD-binding polypeptides into the rhizosphere which are subsequently taken up by the roots and translocated to the shoot via xylem transport.