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

CO 2 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 NaH 14 CO 3 . Samples were taken and analyzed for labelled metabolites after 15 s and 4 min of 14 CO 2 fixation. The results show that in the light both the Calvin cycle and phosphoenolpyruvate carboxylation were observable, whereas in the darkness CO 2 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.