Integrated metabolic and transcriptomic analysis of the duckweed Lemna gibba growing under photomixotrophic conditions: Metabolic adjustments to different nitrogen sources

Duckweeds are small, rapidly growing aquatic flowering plants. Due to their ability for biomass production at high rates they represent promising candidates for biofuel feedstocks. Duckweeds are also excellent model organisms because they can be maintained in well-defined liquid media, usually reproduce asexually, and because genomic resources are becoming increasingly available. To establish a framework for quantitative metabolic research in duckweeds we derived a central carbon metabolism network model of Lemna gibba based on its draft genome. Lemna gibba fronds were grown in a photomixotrophic mode in liquid media under continuous light with 13C-labeled glucose as a carbon source. Two different conditions (nitrate vs. glutamine as nitrogen source) were compared by quantification of growth kinetics, metabolite levels, metabolic flux and transcript abundance. Fronds grown on inorganic nitrogen (nitrate) or on organic nitrogen (glutamine) medium were harvested and immediately frozen in liquid nitrogen. For each condition three biological replicates were analyzed.