ABSTRACT
This chapter presents the methods used for the measurements of fluxes in metabolic pathways. Short-term labelling can be used qualitatively in order to determine the sequence of intermediates of a metabolic pathway. Compartmentalization is a source of error in the interpretation of short-term labelling experiments. In quantitative terms, for groups of atoms derived directly from a precursor, the specific labelling is identical to that of the precursor and the amount of label incorporated is proportionate to the molar quantities of compounds: these data therefore provide no information on fluxes in the metabolic pathway. This approach is based on following the change in enrichments of one/more compounds over time, until the establishment of a steady state. The techniques used to study slow chemical exchange combine spin labelling and longitudinal relaxation. The measurement of fluxes is a key to clarifying the relationships between modifications in the metabolome and transcriptome data that are provided by the analysis of natural or artificial mutant plants.
