Coordinated accumulation of the chloroplastic and cytosolic pyruvate,Pi dikinases with enhanced expression of CAM in Kalanchoë blossfeldiana

Recent studies reveal that the intracellular localization of pyruvate,Pi dikinase (PPDK, EC 2.7.9.1) in mesophyll cells of malic enzyme (ME)-dependent Crassulacean acid metabolism (CAM) plants varies among species, occurring not only in the chloroplasts but also in the cytosol in some species. The facultative CAM plant Kalanchoë blossfeldiana accumulates PPDK in both compartments of the mesophyll cells. In this study, the patterns of accumulation of the chloroplastic and cytosolic PPDKs were investigated for K. blossfeldiana plants with different CAM activities by immunogold labeling and electron microscopy. Greater CAM activity was found in plants grown under drought conditions with short days than under well-watered conditions with long days, and in lower leaves than in higher leaves. There was a trend that plants and leaves with greater CAM activity show denser labeling for PPDK in both the cytosol and chloroplasts. However, the ratio of the density of PPDK labeling in the cytosol to that in the chloroplasts was almost constant (2.4–3.0). Higher labeling for phosphoenolpyruvate carboxylase (EC 4.1.1.31) in the cytosol was also correlated with higher CAM activity but there was almost no difference in the density of labeling for ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) in the chloroplasts. These results indicate that the increase in accumulation of cytosolic PPDK is closely associated with the increase of chloroplastic PPDK during enhanced CAM expression. This suggests that both PPDKs are involved in CAM function.