|Samac, Deborah - Debby|
Submitted to: Nitrogen Fixation International Congress
Publication Type: Abstract Only
Publication Acceptance Date: 7/3/2001
Publication Date: N/A
Technical Abstract: Acid soils and aluminum (Al) toxicity are severe impediments to alfalfa yield and Rhizobium performance in many parts of the world. Organic acids such as malate and citrate are known to alleviate Al toxicity by chelating Al and rendering it less toxic. We produced transgenic alfalfa (Medicago sativa L.) expressing a full-length nodule-enhanced malate dehydrogenase (neMDH) cDNA in the sense orientation under the control of the constitutiv CaMV 35S promoter. Selected transgenic plants displayed enhanced neMDH mRNA, polypeptides, and MDH enzyme specific activity in root-tips, compared to root-tips of untransformed plants. From HPLC analysis, two transgenic plants evaluated showed up to 6-fold greater malate, citrate, oxalate, and succinate content in root tissues as well as increased exudation into the growth media. Nevertheless, transgenic alfalfa showed a reduced biomass accumulation during the first year of growth in field plots of neutral soil l(pH 6.8). In Al-containing acid culture, however, transgenic plants had greater root elongation and higher biomass yield than did untransformed plants. Crosses between transgenic alfalfa and a conventionally bred acid soil tolerant alfalfa exhibited cosegregation of the transgene and altered organic acid content in root-tips. Transgenic alfalfa will be evaluated for nodulation and biological N-fixation ability in acid soils.