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Title: Tracking the metabolic pulse of plant lipid production with isotopic labeling and flux analyses: Past, present and future

item Allen, Douglas - Doug
item BATES, PHILIP - University Of Southern Mississippi
item TJELLSTROM, HENRIK - Michigan State University

Submitted to: Progress in Lipid Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2015
Publication Date: 3/13/2015
Publication URL:
Citation: Allen, D.K., Bates, P.D., Tjellstrom, H. 2015. Tracking the metabolic pulse of plant lipid production with isotopic labeling and flux analyses: Past, present and future. Progress in Lipid Research. 58:97-120.

Interpretive Summary: The value of many agricultural crops is based on the composition of their biomass. Metabolism in the plant that relates to the conversion of sugars into lipids, carbohydrates and protein with the associated production and consumption of energy is a central activity within plant cells and establishes biomass composition. The network of enzymatic reactions that defines metabolic activity is complicated and varies between species and within tissues such as leaves, roots and developing seeds. Additionally, the external environment also directly influences plant metabolism. Here we describe the contribution of isotope labeling strategies (using stable or radioactive isotopes) to determine the operation of metabolic networks and their regulation in plants. Additionally we focus on what has been learned about the production the primary form of storage lipid (triacylglycerol), which is the plant-based commodity used for vegetable oil production and also biodiesel. Isotopic labeling studies are of growing importance because they provide a means to trace metabolites through biochemical pathways without perturbing metabolism. Therefore, they represent an important tool for quantifying the flow of metabolites metabolic through cells and identifying limitations or bottlenecks that preclude a more efficient cellular operation. By using isotope 'tracers' a better understanding of plant metabolism can guide rational metabolic engineering efforts and contribute to increased crop yield with enhanced biomass composition for food, feed and fuel needs.

Technical Abstract: Metabolic networks are comprised of chemical transformations that are the basis of cellular operation and function to sustain life. The molecular rate of transitioning through biochemical pathways (i.e. flux) establishes cellular phenotypes that can be studied in response to genetic or environmental perturbations. Each change evokes a response in metabolic pathway flow and the quantification of fluxes under varied conditions helps to elucidate major and minor routes, and regulatory aspects of metabolism. To measure fluxes requires experimental methods that assess the movements and transformations of metabolites without creating artifacts. Isotopic labeling fills this role and is a long-standing experimental approach to identify pathways and quantify their metabolic relevance in different tissues or under different conditions. The application of labeling techniques to plant science is however far from reaching it potential. In light of advancements in genetics and molecular biology that provide a means to alter metabolism, and given recent improvements in instrumentation, computational tools and available isotopes, the use of isotopic labeling to probe metabolism is becoming more and more powerful. We review the principal analytical methods for isotopic labeling with a focus on seminal studies of pathways and fluxes in lipid metabolism and carbon partitioning through central metabolism. Central carbon metabolic steps are directly linked to lipid production by serving to generate the precursors for fatty acid biosynthesis and lipid assembly. Additionally some of the ideas for labeling techniques that may be most applicable for lipid metabolism in the future have been developed to investigate other aspects of central metabolism. We conclude by describing recent advancements that will play an important future role in quantifying flux and metabolic operation in plant tissues.