Poster: Metabolic engineering

Abs # 292: Characterization of altered metabolism in transgenic alfalfa overexpressing malate dehydrogenase to confer aluminum tolerance

Presenter:	Morphew, Rachel , rjmorphew@viterbo.edu
Authors	Morphew, Rachel  (A)   Arndt, Rebecca  (A)   Lauter, Charles  (A)   Tesfaye, Mesfin  (B)   Samac, Deborah  (B)   Temple, Glena  (A)
Affiliations:	(A): Biology Department, Viterbo University (B): U.S. Department of Agriculture –Agricultural Research Service-Plant Science Unit

Aluminum (Al) toxicity is a severe impediment to production of many crop plants in acid soils. An addition of organic acids into plant nutrient solutions alleviates phytotoxic Al effects, presumably by chelating Al and rendering it less toxic. In an effort to increase organic acid secretion and enhance Al tolerance transgenic alfalfa plants (Medicago sativa) were produced using nodule-enhanced forms of malate dehydrogenase under the control of the cauliflower mosaic virus 35S promoter. These alfalfa plants have been shown to have a 1.6-fold increase in malate dehydrogenase activity in root tips, a 4.2 fold increase in root concentration, and a 7.1-fold increase in root exudation of citrate, oxalate, malate, succinate and acetate compared to untransformed controls. When the plants were grown on naturally acidic, high Al-containing soil, biomass accumulation (shoots and roots) of the transgenic plants was significantly greater than the controls. However, the transgenic alfalfa plants accumulate less biomass compared to control plants in a neutral pH soil (low Al). Root exudation represents an appreciable drain on plant resource, thereby imposing an energy cost to the plants. A significant increase in sucrose levels and a decrease in starch levels were observed in the leaves of the transgenic plants, compared to untransformed controls. Specific activities of glutamine synthase and citrate synthase increased in the leaves of the transgenic plants, while the activity of phosophoenolpyruvate carboxylase decreased compared to the untransformed control. Altering the organic acid synthesis in these transgenic plants causes significant metabolic changes in carbon and nitrogen pathways in the roots and shoots. Results of the biochemistry of these plants will be presented.