NMR adventures in the metabolic labyrinth within plants.

The era of metabolic engineering has begun, but there is only limited knowledge about metabolic fluxes and how they are regulated in plants. Particular challenges are the non-linearities between enzyme abundances, metabolite concentrations and metabolic fluxes, and the existence of metabolic networks that provide multiple routes between many important metabolites. NMR offers the means to distinguish and quantitate the fluxes along different routes to key metabolites. NMR can therefore help us understand and resolve the apparent paradox of, on the one hand, great metabolic flexibility evident in the natural responses of plants and, on the other hand, the unpredictable changes in metabolism reported in genetically engineered plants.