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Title:   Author  item
                                            Samac, Deborah

                                                         - *Debby*item
                                            TESFAYE, MESFIN - UNIVERSITY OF MINNESOTAitem
                                            ALLEN, DEBORAH - UNIVERSITY OF MINNESOTAitem
                                            Vance, Carroll
  Submitted to: Plant and Animal Genome VX Conference Abstracts
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 1/11/2002
                                    Publication  Date: N/A
                                    Citation: N/AInterpretive Summary:
                                Technical Abstract: Acid soils are a severe impediment to crop production in many parts of the world. In mineral soils, aluminum (Al) becomes phytotoxic at acidic pHs, inhibiting root growth and nutrient acquisition. Exposure to Al induces organic acid exudation in a number of Al tolerant plants. Alfalfa (Medicago sativa) plants with constitutive over-expression of an alfalfa nodule-  enhanced malate dehydrogenase (neMDH) cDNA were produced to examine if increased enzyme activity would increase organic acid exudation and enhance Al tolerance. We found that a 1.6-fold increase in MDH specific activity in selected lines increased production of citrate and malate 4.1-fold in roots and increased exudation 2.9-fold over untransformed control plants. These plants also demonstrated enhanced root growth in acidic Al-containing nutrient solutions. In acid soil, root growth of alfalfa transgenics was 2.2-fold that of untransformed plants. Over-expression of neMDH in Medicago otruncatula and oats (Avena sativa) also conferred enhanced Al tolerance. A survey of the microbial diversity in the rhizosphere of transgenic and control alfalfa plants, as revealed by partial 16S rDNA sequencing, indicated that transgenic lines support a greater diversity of bacteria than untransformed control plants. Constitutive expression of neMDH results in reduced shoot biomass accumulation. Plants containing transgene constructs with a root-tip specific promoter from an alfalfa MAP kinase gene are being evaluated for gene expression and Al tolerance. These experiments demonstrate that enhancing organic acid synthesis may be an effective strategy to cope with acid soil and Al toxicity.


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