| Experiments were conducted to investigate role of plants in fate of xenobiotics in aquatic ecosystems with L. minor. Experimental xenobiotics, 2,4-dichlorophenyl (DCP) and 2,4,5-trichlorophenol (TCP), were selected as representative xenobiotics of an important class of contaminants with historical uses in wood treatment and agriculture. Systems were operated in manner allowing microbial interactions with xenobiotics so that plant processes could be investigated in natural contexts.; Xenobiotic removal was rapid with active plant populations. No transformation products were found in media of any experimental system, nor were any observed transformations consistent with microbial processes. In active plants, tissue concentrations of contaminants reached rapid, transient maxima and approached zero at times corresponding to complete removal of contaminant from media.; Two metabolites of DCP, 2,4-dichlorophenyl-β-D-glucopyranoside (DCPG) and 2,4-dichlorophenyl-(6-O-malonyl)-β-D-glucopyranoside (DCPMG), were identified by comparison of chromatographic retention, ESI-MS and 1H-NMR to synthesized reference materials. A third metabolite, 2,4-dichlorophenyl-β-D-glucopyranosyl-β-apiofuranoside, was identified by wet chemical methods and analysis of ESI-MS and 1H-NMR spectra. Similarities in ESI-MS spectra of compounds derived from 2,4,5-trichlorophenol supported identification of TCP metabolites (TCPAG, TCPG, and TCPMG).; Quantitative procedures were developed for DCPG, TCPG, DCPMG, and TCPMG. DCPAG and TCPAG concentrations were estimated from response functions of parent glycosides. Kinetic behavior of identified components, e.g., media DCP, tissue DCP, DCPG, DCPMG and DCPAG, from multiple experiments was analyzed over short (<24 hr) and long (<120hr) time scales and with respect to aqueous removal (conversion). These results were combined with structural characteristics of metabolites to delineate the sequence of assimilation.; Assimilation was initiated by diffusive mass transfer of xenobiotic into plant tissues and subsequent formation of DCPG. DCPG served as the precursor for DCPMG and DCPAG in parallel processes. DCPMG formation was consistent with direct esterification of DCPG and associated with compartmentalization in vacuoles. DCPAG was previously unreported in the literature and formation was shown to be associated with cell-wall polysaccharides of plants.; Identified metabolites represented at least ∼50% of DCP and ∼80% of TCP introduced into systems at times corresponding to complete conversion. Thus, the pathway delineated here had a significant role in environmental fate of xenobiotics. |
