Fixation and metabolism of carbon dioxide by photosynthetically active carrot callus cultures

CO2 fixation experiments with photosynthetically active 3-week-old carrot callus cultures (60–90 μg chlorophyll∙g fresh weight−1) were carried out in light and darkness in nutrient solution containing NaH14CO3. Samples were taken and analyzed for labelled metabolites after 15 s and 4 min of 14CO2 fixation. The results show that in the light both the Calvin cycle and phosphoenolpyruvate carboxylation were observable, whereas in the darkness CO2 was fixed only by phosphoenolpyruvate carboxylation. However, extractable phosphoenolpyruvate carboxylation activity was reduced by about 80% upon darkening the light-grown cultures for 1.5 h.