Journal Article

Magnesium Ameliorates Aluminum Rhizotoxicity in Soybean by Increasing Citric Acid Production and Exudation by Roots

Ivo R. Silva, Thomas J. Smyth, Daniel W. Israel, Charles D. Raper and Thomas W. Rufty

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 42, issue 5, pages 546-554
Published in print May 2001 | ISSN: 0032-0781
Published online May 2001 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pce067
Magnesium Ameliorates Aluminum Rhizotoxicity in Soybean by
Increasing Citric Acid Production and Exudation by
Roots

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Superior effectiveness of Mg over Ca in alleviating Al rhizotoxicity cannot be accounted for by predicted changes in plasma membrane Al3+ activity. The influence of Ca and Mg on the production and secretion of citrate and malate, and on Al accumulation by roots was investigated with soybean genotypes Young and PI 416937 which differ in Al tolerance. In the presence of a solution Al3+ activity of 4.6 µM, citrate and malate concentrations of tap root tips of both genotypes increased with additions of either Ca up to 3 mM or Mg up to 50 µM. Citrate efflux rate from roots exposed to Al was only enhanced with Mg additions and exceeded malate efflux rates by as much as 50-fold. Maximum citrate release occurred within 12 h after adding Mg to solution treatments. Adding 50 µM Mg to 0.8 mM CaSO4 solutions containing Al3+ activities up to 4.6 µM increased citrate concentration of tap root tips by 3- to 5-fold and root exudation of citrate by 6- to 9-fold. Plants treated with either 50 µM Mg or 3 mM Ca had similar reductions in Al accumulation at tap root tips, which coincided with the respective ability of these ions to relieve Al rhizotoxicity. Amelioration of Al inhibition of soybean root elongation by low concentrations of Mg in solution involved Mg-stimulated production and efflux of citrate by roots.

Keywords: Key words: Aluminum tolerance — Calcium — Cation amelioration — Magnesium — Organic acids — Root exudates — Soybean.; Abbreviations: Al, aluminum; Ca, calcium; Mg, magnesium; Si, silicon.

Journal Article.  6246 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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