Histochemical Compartmentation of Photosynthesis in the Crassulacean Acid Metabolism Plant Crassula falcata.

The succulent leaf of the obligate Crassulacean acid metabolism plant Crassula falcata comprises two distinct types of parenchyma. The peripheral tissue is dark green, whereas the central tissue is relatively colorless. We have investigated whether the conventional interpretation of Crassulacean acid metabolism-simply, temporal separation of light and dark CO(2) fixation within individual cells-is sufficient. Ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) and chlorophyll, indicating the photosynthetic-carbon-reduction pathway, were concentrated in peripheral tissue. Specific activities of P-enolpyruvate carboxylase (4.1.1.31) and of NAD(+)-malic enzyme (1.1.1.39), indicating capacity for dark CO(2) fixation and release, respectively, were high in both types of parenchyma. Measured directly as malic acid decline at the beginning of the photoperiod, CO(2) "storage" occurred in both tissues. These data indicate that there is a spatial component to Crassulacean acid metabolism in C. falcata.