caa a22 4500 47710097X CHVBK 20180405111541.0 cr unu---uuuuu 170330e19960401xx s 000 0 eng 10.1007/BF00262634 doi (NATIONALLICENCE)springer-10.1007/BF00262634 Diurnal modulation of phosphoenolpyruvate carboxylation in pea leaves and roots as related to tissue malate concentrations and to the nitrogen source [Elektronische Daten] [Laurent Leport, Andrea Kandlbinder, Bernhard Baur, Werner Kaiser] Phosphoenolpyruvate (PEP) carboxylation was measured as dark 14CO2 fixation in leaves and roots (in vivo) or as PEP carboxylase (PEPCase) activity in desalted leaf and roof extracts (in vitro) from Pisum sativum L. cv. Kleine Rheinländerin. Its relation to the malate content and to the nitrogen source (nitrate or ammonium) was investigated. In tissue from nitrate-grown plants, PEP carboxylation varied diurnally, showing an increase upon illumination and a decrease upon darkening. Diurnal variations in roots were much lower than in leaves. Fixation rates in leaves remained constantly low in continuous darkness or high in continuous light. Dark CO2 fixation of leaf slices also decreased when leaves were preilluminated for 1 h in CO2-free air, suggesting that the modulation of dark CO2 fixation was related to assimilate availability in leaves and roots. Phosphoenolpyruvate carboxylase activity was also measured in vitro. However, no difference in maximum enzyme activity was found in extracts from illuminated or darkened leaves, and the response to substrate and effectors (PEP, malate, glucose-6-phosphate, pH) was also identical. The serine/threonine protein kinase inhibitors K252b, H7 and staurosporine, and the protein phosphatase 2A inhibitors okadaic acid and cantharidin, fed through the leaf petiole, did not have the effects on dark CO2 fixation predicted by a regulatory system in which PEPCase is modulated via reversible protein phosphorylation. Therefore, it is suggested that the diurnal modulation of PEP carboxylation in vivo in leaves and roots of pea is not caused by protein phosphorylation, but rather by direct allosteric effects. Upon transfer of plants to ammonium-N or to an N-free nutrient solution, mean daily malate levels in leaves decreased drastically within 4-5 d. At that time, the diurnal oscillations of PEP carboxylation in vivo disappeared and rates remained at the high light-level. The coincidence of the two events suggests that PEPCase was de-regulated because malate levels became very low. The drastic decrease of leaf malate contents upon transfer of plants from nitrate to ammonium nutrition was apparently not caused by increased amino acid or protein synthesis, but probably by higher decarboxylation rates. Springer-Verlag, 1996 Ammonium nationallicence Malate nationallicence Nitrate nationallicence Phosphoenolpyruvate carboxylase nationallicence Protein phosphorylation nationallicence CAM : crassulacean acid metabolism nationallicence PEP : Phosphoenolpyruvate nationallicence PEPCase : phosphoenolpyruvate carboxylase nationallicence PP : protein phosphatase nationallicence PK : protein kinase nationallicence Leport Laurent Center for legumes in mediterranean agriculture, University of Western Australia, 6009, Nedlands, WA, Australia aut Kandlbinder Andrea Julius-von-Sachs-Institut für Biowissenschaften, Universität Würzburg, Mittlerer Dallenbergweg 64, D-97082, Würzburg, Germany aut Baur Bernhard Julius-von-Sachs-Institut für Biowissenschaften, Universität Würzburg, Mittlerer Dallenbergweg 64, D-97082, Würzburg, Germany aut Kaiser Werner Julius-von-Sachs-Institut für Biowissenschaften, Universität Würzburg, Mittlerer Dallenbergweg 64, D-97082, Würzburg, Germany aut Planta Springer-Verlag 198/4(1996-04-01), 495-501 0032-0935 198:4<495 1996 198 425 https://doi.org/10.1007/BF00262634 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00262634 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Leport Laurent Center for legumes in mediterranean agriculture, University of Western Australia, 6009, Nedlands, WA, Australia aut NATIONALLICENCE 700 1- Kandlbinder Andrea Julius-von-Sachs-Institut für Biowissenschaften, Universität Würzburg, Mittlerer Dallenbergweg 64, D-97082, Würzburg, Germany aut NATIONALLICENCE 700 1- Baur Bernhard Julius-von-Sachs-Institut für Biowissenschaften, Universität Würzburg, Mittlerer Dallenbergweg 64, D-97082, Würzburg, Germany aut NATIONALLICENCE 700 1- Kaiser Werner Julius-von-Sachs-Institut für Biowissenschaften, Universität Würzburg, Mittlerer Dallenbergweg 64, D-97082, Würzburg, Germany aut NATIONALLICENCE 773 0- Planta Springer-Verlag 198/4(1996-04-01), 495-501 0032-0935 198:4<495 1996 198 425 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer