Figure 3.

Chloroplast and mitochondrial transport responses at low light levels. This shows a magnified view of the transition between the states A and B shown in Figure 2. At lowest light levels, there is a maximum import of 3-phosphoglycerate (3-PGA) into the chloroplast, corresponding with the maximum export of glyceraldehyde 3-P (GAP), acting as a shuttle to export reductant and ATP. At the same point, the mitochondrial malate-oxaloacetate (Mal-OAA) shuttle is maximally active, as demonstrated by the import of Mal, the activity of malate dehydrogenase (MalDH), and the export of OAA. Thus, in this region, there is a net transfer of reductant from the chloroplast to the cytosol. The two curves for CO₂ transport demonstrate the recycling from mitochondria to chloroplast.