Specific 13C enrichments of the carbon atoms of soluble sugars
Maize root tips were incubated for 25 h with 200 mm d-[1-13C]Glc. The Glc and Suc were purified by HPLC and analyzed by 1H- and 13C-NMR. The enrichment values of the C-1 carbons were calculated from 1H-NMR spectra, those of the C-2 to C-6 carbons, from 13C-NMR spectra. The results reported as measured enrichments are the average ±sd of five independent experiments. For Glc and Suc, as the enrichments of carbons C-2 to C-5 are close to natural abundance, they are not reported in the table. The measured enrichments obtained after a steady-state labeling with [1-13C]Glc were corrected by the diluting factor according to the following formula: Ecorrected = (Emeasured − 1.1). DF + 1.1, where DF is the diluting factor (see “Materials and Methods”), 1.066 and 1.038 for Glc and Suc, respectively. These values are reported as corrected enrichments.