Plant and Cell Physiology Advance Access originally published online on April 8, 2005
Plant and Cell Physiology 2005 46(6):892-901; doi:10.1093/pcp/pci094
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A Link Between Citrate and Proton Release by Proteoid Roots of White Lupin (Lupinus albus L.) Grown Under Phosphorus-deficient Conditions?
1 Institute of Plant Nutrition, Interdisciplinary Research Center, Justus Liebig University, Heinrich-Buff-Ring 26–32, D-35392 Giessen, Germany
2 Institute of Crop Science and Plant Breeding I, Justus Liebig University, Ludwigstrasse 23, D-35390 Giessen, Germany
4 Corresponding author: E-mail, feng.yan{at}agrar.uni-giessen.de; Fax, +49-641-99-37449.
White lupin (Lupinus albus L.) is able to acclimate to phosphorus deficiency by forming proteoid roots that release a large amount of citric acid, resulting in the mobilization of sparingly soluble soil phosphate in the rhizosphere. The mechanisms responsible for the release of organic acids have not been fully elucidated. In this study, we focused on the link between citrate and malate release and the release of H+ and other inorganic ions by proteoid roots of white lupin. The release of citrate was closely correlated with the release of H+, K+, Na+ and Mg2+, but not with that of Ca2+. The stoichiometric relationships between citrate release and the release of H+, K+, Na+ and Mg2+ were 1 : 1.3, 1 : 2.1, 1 : 1.5 and 1 : 0.47, respectively. Similar correlations were found between exudation of malate and cations. During 30 min incubation, fusicoccin addition stimulated H+ and malate release, but not citrate release. A concomitant stimulation of H+, malate and citrate release was measured after 60 min incubation. Vanadate inhibited the release of H+ and malate, but not that of citrate. Anthracene-9-carboxylic acid, an anion channel blocker, caused a concomitant decrease in release of citrate, malate and H+. We conclude that for export of citrate across the plasma membrane of proteoid root cells, H+ release is not strictly related to citrate release. Other cations such as K+ and Na+ can also serve as counterions for citrate release. In contrast, malate release shows a strong H+ release dependency.
3 Present address: College of Resources and Environment Sciences, Nanjing Agricultural University, Weigang 1, 210095 Nanjing, P.R. China.
(Received February 4, 2005; Accepted March 21, 2005)
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  H. LAMBERS, M. W. SHANE, M. D. CRAMER, S. J. PEARSE, and E. J. VENEKLAAS Root Structure and Functioning for Efficient Acquisition of Phosphorus: Matching Morphological and Physiological Traits Ann. Bot., October 1, 2006; 98(4): 693 - 713. [Abstract] [Full Text] [PDF]
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