CHANGES IN LEVELS OF PHOSPHOENOLPYRUVATE CARBOXYLASE WITH INDUCTION OF CRASSULACEAN ACID METABOLISM (CAM)-LIKE BEHAVIOR IN THE C-4 PLANT PORTULACA-OLERACEA

Changes in levels of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.3 1, orthophosphate: oxaloacetate carboxy-lyase, phosphorylating) were f ollowed in leaves and stems of CAM-expressing and non-expressing Portu laca oleracea L. plants. CAM expression was induced by growing plants under an 8-h photoperiod and water stress conditions (SD-WS). Leaves a nd stems of these plants (designated CAM) expressed nocturnal acidific ation with an oscillation pattern and an amplitude characteristic of C AM plants. Generally, PEPC activity increased by ca 3-fold during the period of CAM induction. Over the day/night cycle, PEPC activity oscil lated in a pattern typical of CAM plants. Treatment of the other plant group (designated as non-CAM) by growth under a 16-h photoperiod and well-watered conditions (LD-WW) did not induce expression of the teste d criteria of CAM in plants. In these plants, nocturnal acidification as well as changes in the magnitude of PEPC activity and fluctuation p attern were undetectable. SDS-PAGE of leaf extracts of the CAM-express ing plants and the corresponding densitometric scans show progressive increase in the amount of PEPC subunit protein (ca 95 kDa) during the period of CAM induction. These results show that induction of CAM-like characteristics in the C-4 plant Portulaca oleracea is also accompani ed by increased PEPC activity, which may be partly due to an increase in enzyme synthesis.