CHANGES IN LEVELS OF PHOSPHOENOLPYRUVATE CARBOXYLASE WITH INDUCTION OF CRASSULACEAN ACID METABOLISM (CAM)-LIKE BEHAVIOR IN THE C-4 PLANT PORTULACA-OLERACEA
Ama. Mazen, CHANGES IN LEVELS OF PHOSPHOENOLPYRUVATE CARBOXYLASE WITH INDUCTION OF CRASSULACEAN ACID METABOLISM (CAM)-LIKE BEHAVIOR IN THE C-4 PLANT PORTULACA-OLERACEA, Physiologia Plantarum, 98(1), 1996, pp. 111-116
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.