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United States Department of Agriculture

Agricultural Research Service

Title: The Influence of Organic Acid Exudation in Alfalfa on Aluminum Tolerance, Nutrient Acquisition, and Bacterial Diversity

item Samac, Deborah

Submitted to: Information Systems for Biotechnology News Report
Publication Type: Review Article
Publication Acceptance Date: October 1, 2003
Publication Date: November 1, 2003
Citation: Samac, D.A. 2003. Influence of organic acid exudation in alfalfa on aluminum tolerance, nutrient acquisition, and bacterial diversity. Information Systems for Biotechnology News Report. Available:

Technical Abstract: Acid soil is a major constraint to crop production in many parts of the world. In mineral acid soils, aluminum (Al) toxicity is the major factor leading to reduced plant growth. Several strategies have been pursued to manage acid soils including liming and application of phosphorus, organic soil amendments, and development of tolerant plant varieties by classical breeding and transgenic approaches. In an effort to increase tolerance of alfalfa to Al, we generated transgenic alfalfa plants with gene constructs designed to increase organic acid synthesis. Organic acids have been shown to chelate Al and prevent uptake from the soil. Over-expression of a nodule-enhanced form of malate dehydrogenase (neMDH) was found to increase organic acid production and aluminum tolerance in acid conditions. Compared to untransformed control plants, those expressing the neMDH transgene accumulated higher amounts of phosphorus and the soil surrounding these plants had higher levels of soil macro- and micronutrients. Bacterial populations were distinctly different in soil surrounding roots of the transgenic plants compared to the untransformed plants. These results suggest that the organic acids produced are excreted under field conditions. Thus, modification of MDH expression in alfalfa shows promise for improving plant adaptation and plant performance in marginal soils.

Last Modified: 4/22/2015
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