Table II.

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: E_corrected = (E_measured − 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.

	Glucose	Sucrose
			Glucosyl	Fructosyl
Measured enrichments (%)
C-1	73.8 ± 1.0	73.8 ± 0.8	70.8 ± 1.5
C-6	14.6 ± 1.3	17.2 ± 1.5	19.2 ± 1.2
Corrected enrichments (%)
C-1	78.6 ± 2.7	76.6 ± 1.1	73.4 ± 1.8
C-6	15.5 ± 1.7	17.8 ± 1.6	19.9 ± 1.3