In vivo phosphorylation of phosphoenolpyruvate carboxylase in Egeria densa, a submersed aquatic species

LARA, MARIA V.; CASATI, PAULA; ANDREO, CARLOS S.; LARA, MARÍA VALERIA

PLANT AND CELL PHYSIOLOGY

OXFORD UNIV PRESS

Año: 2001 vol. 42 p. 441 - 445

0032-0781

The C4 succulent plant Portulaca oleracea shifts itsphotosynthetic metabolism to crassulacean acid metabolism(CAM) after 23 d of withholding water. This isaccounted by diurnal acid fluctuation, net nocturnal butnot day CO2 uptake and drastic changes in phosphoenolpyruvatecarboxylase (PEPC) kinetic and regulatoryproperties [Lara et al. (2003) Photosynth. Res. 77: 241]. Thegoal of the present work was to characterize the CAMactivity in leaves of P. oleracea during water stress throughthe study of enzymes involved in carbon fixation and carbohydratemetabolism. After drought stress, a generaldecrease in the photosynthetic metabolism, as accounted bythe decrease in the net CO2 fixation and in the activity ofenzymes such as ribulose-1,5-bisphosphate carboxylase/oxygenase, PEPC, pyruvate orthophosphate dikinase, phosphoenolpyruvatecarboxykinase and NAD-malic enzymewas observed. We also found changes in the day/night activitiesand level of immunoreactive protein of some of theseenzymes which were correlated to night CO2 fixation, asoccurs under CAM metabolism. Based on the resultsobtained, including those from in situ immunolocalizationstudies, we propose a scheme for the possible CO2 fixationpathways used by P. oleracea under conditions of sufficientand limiting water supply.