Effect of leaf age on CAM activity in Littorella uniflora

The capacity for both CAM and photosynthesis declined with increasing leaf age, and was in the oldest leaves only 25-53% of the capacity in the youngest. The photosynthetic capacity was estimated to be sufficiently high to ensure refixation of the CO2 released from malate during decarboxylation in the daytime. In line with this, a linear coupling between CAM capacity and photosynthetic capacity was found. Parallel to the change in photosynthetic capacity, an age-related change in total ribulose-bisphosphate carboxylase/oxygenase (rubisco) activity from 732 μmol C g−1 DW h−1 in the youngest leaves to 346 μmol C g−1 DW h−1 in the oldest was observed. In contrast, no significant change in phosphoenolpyruvate carboxylase (PEPcase) activity with leaf age was observed (means ranged between 46 and 156 μmol C g−1 DW h−1).