Validation of the design of feeding experiments involving [14C]substrates used to monitor metabolic flux in higher plants

The use of ratios of 14CO2 release from different combinations of positionally labelled [14C]substrates to provide information on flux through the principal pathways of carbohydrate oxidation is validated. Metabolism in Arabidopsis thaliana cell suspension cultures was unaffected by the presence of alkali used to trap respired 14CO2. Although capture of released label was incomplete, alkali traps absorbed a representative proportion of 14CO2 generated by metabolism, and reassimilation of released 14CO2 was negligible. However, caution is needed in evaluating the absolute amount of 14CO2 generated in typical feeding studies.