Carrier-Mediated Uptake and Phloem Systemy of a 350-Dalton Chlorinated Xenobiotic with an α-Amino Acid Function

• Published in: Plant physiology (Bethesda) Vol. 125; no. 4; pp. 1620 - 1632
• Main Authors: Céline Delétage-Grandon, Jean-François Chollet, Faucher, Mireille, Francoise Rocher, Komor, Ewald, Bonnemain, Jean-Louis
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01.04.2001
• Subjects: 4-Chloromercuribenzenesulfonate - pharmacology; Acidic amino acids; Amino acids; Autoradiography; Basic amino acids; Biological and medical sciences; Biological Transport - drug effects; Carbonyl Cyanide m-Chlorophenyl Hydrazone - pharmacology; Cell Biology and Signal Transduction; Chemical control; Fabaceae - physiology; Fundamental and applied biological sciences. Psychology; Kinetics; Leaves; Lysine - analogs & derivatives; Lysine - chemical synthesis; Lysine - chemistry; Lysine - pharmacokinetics; Models, Molecular; Molecular Conformation; Molecules; Parasitic plants. Weeds; Phloem; Phytopathology. Animal pests. Plant and forest protection; Plant Leaves - drug effects; Plant Leaves - physiology; Plant physiology and development; Plants; Plants, Medicinal; Potassium Chloride - pharmacology; Protoplasts; Tritium; Water and solutes. Absorption, translocation and permeability; Weeds; Xenobiotics; Xenobiotics - chemical synthesis; Xenobiotics - chemistry; Xenobiotics - pharmacokinetics; Translocation; Active transport; 2,4-D; Biological transport; Pesticides; Mobility; Herbicide; Specificity; Absorption; Phloem; Lysine; Aminoacid; Phytohormone; Aryloxyacetic acids; Conjugated compound; Conductive tissue; Xenobiotic; Carrier protein
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.125.4.1620

In a previous paper we have shown that ε-(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 ε-(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 ($K_{\text{m}}1$ = 0.2 mM; $V_{\text{max}}1$ = 2.4 nmol cm-2 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.