Carrier-mediated uptake and phloem systemy of a 350-Dalton chlorinated xenobiotic with an alpha-amino acid function.
In a previous paper we have shown that epsilon-(phenoxyalkanecarboxylyl)-L-Lys conjugates are potent inhibitors of amino acid transport systems and that it is possible to modulate the uptake inhibition by hydrophobic or hydrophilic additions in the 4-position of the aromatic ring (J.F. Chollet, C. Delétage, M. Faucher, L. Miginiac, J.L. Bonnemain [1997] Biochem Biophys Acta 1336: 331-341). In this report we demonstrate that epsilon-(2,4-dichlorophenoxyacetyl)-L-Lys (2,4D-Lys), one of the largest molecules of the series and one of the most potent inhibitors, is a highly permeant conjugate. Uptake of 2,4D-Lys by broad bean (Vicia faba) leaf discs is mediated by an active carrier system (Km1 = 0.2 mM; Vmax1 = 2.4 nmol x cm(-2) x h(-1) at pH 5.0) complemented by an important diffusive component. Among the compounds tested (neutral, basic, and acidic amino acids, auxin, glutathione, and sugars), only the aromatic amino acids clearly compete with 2,4D-Lys. The conjugate accumulates in the vein network, is exported toward the growing organs, and exhibits a distribution pattern different from that of the herbicide moiety. However, over time 2,4D-Lys progressively splits into 2,4D and lysine. Analyses by high-performance liquid chromatography and liquid scintillation spectrometry of the phloem sap collected from the castor bean system, used as a systemy test, indicate decreasing capacities of 2,4D, 2,4D-Lys, and glyphosate, respectively, to move from the epidermis cell wall to the sieve element. Our results show that it is possible to design synthesis of large-size xenobiotics (approximately 350 D) with a lipophilic pole, exhibiting high mobility within the vascular system.
Delétage-Grandon
C
C
Laboratoire de Physiologie et Biochimie Végétales (Unité Mixte de Recherche 6161, Centre National de la Recherche Scientifique), Université de Poitiers, 25 rue du Faubourg, St. Cyprien, 86000 Poitiers, France.
Chollet
J F
JF
Faucher
M
M
Rocher
F
F
Komor
E
E
Bonnemain
J L
JL
D002731:4-Chloromercuribenzenesulfonate / Q000494:pharmacology; D001345:Autoradiography; D001692:Biological Transport / Q000187:drug effects; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D007887:Fabaceae / Q000502:physiology*; D007700:Kinetics; D008239:Lysine / Q000031:analogs & derivatives / Q000138:chemical synthesis / Q000737:chemistry / Q000493:pharmacokinetics*; D008958:Models, Molecular; D008968:Molecular Conformation; D018515:Plant Leaves / Q000187:drug effects / Q000502:physiology; D010946:Plants, Medicinal; D011189:Potassium Chloride / Q000494:pharmacology; D014316:Tritium; D015262:Xenobiotics / Q000138:chemical synthesis / Q000737:chemistry / Q000493:pharmacokinetics*
D015262:Xenobiotics; C431516:epsilon-(2,4-dichlorophenoxyacetyl)lysine; D014316:Tritium; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D002731:4-Chloromercuribenzenesulfonate; D011189:Potassium Chloride; D008239:Lysine