Figure 6.

Model of photosynthetic carbon metabolism including sources of unlabeled carbon that is imported into the Calvin–Benson cycle. The import of unlabeled carbon that enters as hexose slows the rate of labeling of Calvin–Benson cycle intermediates. The G6P shunt also releases moderately labeled CO₂ that can be detected as ¹²CO₂ emitted into a 99+% ¹³CO₂ atmosphere. Abbreviations as in Fig. 1 plus 6PGL, 6-phosphoglucanolactone; 6PG, 6-phosphogluconate; XPT, xylulose 5-phosphate/phosphate antiporter (also transports Ru5P). A detailed flux map based on this model is available in Xu et al. (2022).