Carrier-mediated uptake and phloem systemy of a 350-dalton chlorinated xenobiotic with an alpha-amino acid function

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Delétage-Grandon, Céline ; Chollet, Jean-François ; Faucher, Mireille ; Rocher, Françoise ; Komor, Ewald ; Bonnemain, Jean-Louis:
Carrier-mediated uptake and phloem systemy of a 350-dalton chlorinated xenobiotic with an alpha-amino acid function.
In: Plant Physiology. Bd. 125 (2001) Heft 4 . - S. 1620-1632.
ISSN 1532-2548

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Abstract

"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. Deletage, 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 (K(m)1 = 0.2 mM; V(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 highperformance 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."