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Title:   Author  item
                                            Samac, Deborah

                                                         - *Debby*item
                                            GEBEYAW, MESFIN - UNIVERSITY OF MINNESOTAitem
                                            FEDOROVA, MARIA - UNIVERSITY OF MINNESOTAitem
                                            ALLAN, DEBORAH - UNIVERSITY OF MINNESOTAitem
                                            Vance, Carroll
  Submitted to: Meeting Abstract
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 11/19/2000
                                    Publication  Date: N/A
                                    Citation: N/AInterpretive Summary:
                                Technical Abstract: Acid soils are a severe impediment to the growth of crops in many areas of the world. Under low pH conditions, aluminum (Al) in soil becomes soluble and phytotoxic. Plants suffering from Al toxicity have reduced capacity for water and nutrient uptake, and significantly reduced yields. Engineering plants for synthesis and secretion of organic acids from roots is a highly  promising strategy for conferring Al tolerance. Organic acids chelate Al, blocking uptake by plants. We generated transgenic M. sativa plants over- expressing enzymes for organic acid accumulation and exudation, including phosphoenolpyruvate carboxylase and a unique form of malate dehydrogenase (MDH). Selected lines with enhanced enzyme activity synthesized increased amounts of malate and acidified the medium around growing root tips. Root growth of these lines in 50 æM Al3+ was 3.2 to 4.7-fold greater than root growth of wild type plants. Moreover, transgenic plants tolerated  hydroponic solutions containing up to 100 uM Al3+, which completely inhibited root growth of control plants. Microarrays of Medicago truncatula expressed sequence tags (ESTs) were used to identify alterations in gene expression and the metabolic consequences of overexpression of genes for organic acid synthesis. ESTs putatively associated with aluminum tolerance will also be described.


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