Characterization of Photorespiration in Intact Leaves Using 13Carbon Dioxide Labeling

Abstract
The 13C NMR spectra of sucrose extracted from intact soybean [Glycine max cv. Wayne] and corn [Zea mays cv. Golden Miniature] leaves labeled with 13CO2 for 5-180 min were obtained at 22.6 MHz. The spectra provide a direct determination of the relative concentrations of 12C-13C and 13C-13C pairs of carbons in the labeled triose components of sucrose. This distribution of label is strongly dependent on the O2 concentrations used during labeling for soybean but not for corn. Based on the time dependence of the experimental labeling patterns, photorespiration in air appears to be a sizable fraction of the apparent photosynthetic rate for soybean, but not for corn.