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Plant Physiology Preview Published on November 6, 2003; 10.1104/pp.103.029215
Received June 26, 2003 Effect of Manganese Toxicity on the Proteome of the Leaf Apoplast in Cowpea
Institute of Plant Nutrition, University of Hannover, Herrenhäuser Strasse 2, 30419 Hannover, Germany (M.M.F.-C., W.J.H.); Department of Applied Genetics, University of Hannover, Herrenhäuser Strasse, 30419 Hannover, Germany (H.-P.B.); and Laboratoire de Spectrométrie de Masse Bioorganique, Unité Mixte de Recherche 7509, 25 rue Becquerel, F-67087 Strasbourg cedex 2, France (C.L.-G., A.V.) * Corresponding author; email: horst{at}pflern.uni-hannover.de.
Excess manganese (Mn) supply causes formation of visible brown depositions in the cell walls of leaves of cowpea (Vigna unguiculata), which consist of oxidized Mn and oxidized phenols. Because oxidation of Mn and phenolic compounds in the leaf apoplast was proposed to be catalyzed by apoplastic peroxidases (PODs), induction of these enzymes by Mn excess was investigated. POD activity increased upon prolonged Mn treatment in the leaf tissue. Simultaneously, a significant increase in the concentration of soluble apoplastic proteins in "apoplastic washing fluid" was observed. The identity of the released proteins was systematically characterized by analysis of the apoplast proteome using two-dimensional gel electrophoresis and liquid chromatography-tandem mass spectrometry. Some of the identified proteins exhibit sequence identity to acidic PODs from other plants. Several other proteins show homologies to pathogenesis-related proteins, e.g. glucanase, chitinase, and thaumatin-like proteins. Because pathogenesis-related-like proteins are known to be induced by various other abiotic and biotic stresses, a specific physiological role of these proteins in response to excess Mn supply remains to be established. The specific role of apoplastic PODs in the response of plants to Mn stress is discussed.
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