Induction of a CAM-like metabolism in the succulent C4 plant Portulaca oleracea physiological and morphological changes are accompanied by specific modifications in phosphorenolpyruvate carboxylase

LARA, MV; DISANTE, K.; PODESTA, FE; ANDREO, CS; MARIA FABIANA DRINCOVICH

PHOTOSYNTHESIS RESEARCH

SPRINGER

Año: 2003 vol. 77 p. 241 - 254

0166-8595

The induction of a Crassulacean Acid like Metabolism (CAM) was evidenced after 21-23 days of drought stress in the C4 succulent plant Portulaca oleracea L. by changes in the CO2 exchange pattern, in malic acid content and in titratable acidity during the day-  night cycle. Light microscopy studies also revealed differences in the leaf structure after the drought treatment. Following the induction of the CAM-like metabolism, the regulatory properties of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31), the enzyme responsible for the diurnal fixation of CO2 in C4 plants but nocturnal in CAM plants, were studied. The enzyme from stressed plants showed differential kinetic properties with respect to controls, notably its lack of cooperativity, higher sensitivity to l-malate inhibition, higher PEP affinity and lower enzyme content on a protein basis. PEPC immunolocalization studies showed no differential localization of the enzyme after the drought treatment. In both conditions, PEPC´s subunit size was of 110 kDa, although changes in the isoelectric point and electrophoretic mobility of the native enzyme were observed. In vivo phosphorylation and native isoelectrofocusing studies indicated variations in the phosphorylation status of the enzyme of samples collected during the night and day which was opposite for the control and stressed groups of plants. The results presented suggest that PEPC activity and regulation are modified upon drought stress treatment in a way that allows P. oleracea to perform a CAM-like metabolism