Submitted to: North American Alfalfa Improvement Conference
Publication Type: Abstract Only
Publication Acceptance Date: July 29, 2002
Publication Date: July 29, 2002
Citation: SAMAC, D.A., GEBEYAW, M.T., ALLAN, D.L., VANCE, C.P. GENETIC MANIPULATION OF ALFALFA FOR ORGANIC ACID SYNTHESIS AND ALUMINUM TOLERANCE. 38TH NORTH AMERICAN ALFALFA IMPROVEMENT CONFERENCE. 2002. ABSTRACT. P. 26. 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 acid pH, inhibiting root growth and nutrient acquisition. Engineering plants for synthesis and secretion of organic acids from roots is a highly promising strategy for conferring Al tolerance. In an effort to increase organic acid secretion and thereby enhance Al tolerance in alfalfa, we produced transgenic plants using nodule-enhanced forms of phosphoenolpyruvate carboxylase (nePEPC) and a unique form of malate dehydrogenase (neMDH). We found that a 1.6-fold increase in MDH specific activity in selected transformed lines increased concentration of citrate and malate 4.2-fold in roots and increased exudation of citrate, malate, oxalate, succinate, and acetate 7.1-fold over untransformed control plants. Overexpression of nePEPC increased organic acid concentrations in roots but did not increase the amounts of organic acids in root exudates. Plants with either the neMDH or nePEPC transgene demonstrated enhanced root growth in acidic Al-containing nutrient solutions. In acid soil, root and shoot growth were significantly greater in plants containing the neMDH transgene than in the untransformed control or the line containing the nePEPC transgene. Constitutive expression of neMDH results in reduced shoot biomass accumulation during plant establishment. Plants containing transgene constructs with a root-tip specific promoter 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.