Changes in Levels of Phosphoenolpyruvate Carboxylase with Induction of Crassulacean Acid Metabolism in Mesembryanthemum crystallinum L.

Expanded leaves of Mesembryanthemum crystallinum L. performing C3 photosynthesis were induced to perform pronounced Crassulacean acid metabolism (CAM) by exposing the plant roots to higher NaCl concentration. Levels of phosphoenolpyruvate (PEP) carboxylase activity increased 10-fold during the 7-day induction period. Densitometric analysis of Coomassie-stained sodium dodecyl sulfate (SDS) polyacrylamide gradient slab gels of leaf extracts, prepared during the course of CAM induction, revealed that at least five bands of polypeptides increased in content (kilodalton values of 98, 91, 45, 41, 38). Higher levels of three additional polypeptides (kilodalton values of 102, 76, 33) became apparent after tissue had been grown for 2 weeks at 400 mM NaCl. Of these polypeptides, that having a mass of 98 kilodaltons was identified as the subunit of PEP carboxylase by comparison with the corresponding band from partially purified PEP carboxylase from the same tissue. Only a faint 98 kilodalton band was evident on SDS gels for tissue operating in the C3 mode; staining intensity at this location increased with increasing NaCl-salinity in the rooting medium until CAM was fully induced. These data provide evidence for net synthesis of PEP carboxylase and several other proteins during the induction of CAM in M. crystallinum.