Glycosidation of chlorophenols by Lemna minor



Metabolic fate of xenobiotics in plant tissues has an important role in the ultimate fate of these compounds in natural and engineered systems. Chlorophenols are an important class of xenobiotics used in a variety of biocides and have been shown to be resistant to microbial degradation. Three chlorophenyl glycosides were extracted from tissues of Lemna minor exposed to 2,4-dichlorophenol (DCP). The products were identified as 2,4-dichlorophenyl-β-D-glucopyranoside (DCPG), 2,4-dichlorophenyl-β-D-(6-O-malonyl)-glucopyranoside (DCPMG) and 2,4-dichlorophenyl-β-D-glucopyranosyl-(6→1)-β-D-apiofuranoside (DCPAG). Identification was based on reverse phase retention (C18), electrospray mass spectra collected in negative and positive mode (ESI-NEG and ESI-POS, respectively), and nuclear magnetic resonance (NMR) spectra comparisons to reference materials synthesized in the laboratory. Liquid chromatography-mass spectrometry (LC-MS) analysis of plants exposed to 2,4,5-trichlorophenol (TCP) formed analogous compounds: 2,4,5-trichlorophenyl-β-D-glucopyranoside (TCPG), 2,4,5-trichlorophenyl-β-D-(6-O-malonyl)-glucopyranoside (TCPMG) and 2,4,5-trichlorophenyl-β-D-glucopyranosyl-(6→1)-β-D-apiofuranoside (TCPAG). Enzyme catalyzed hydrolysis with β-glucosidase was ineffective in releasing the β-glucosides with chemical modifications at C6. Presence of these glucoconjugates confirmed that L. minor was capable of xenobiotic uptake and transformation. Identification of these products suggested that chlorophenols were incorporated into vacuoles and cell walls of L. minor.