title: Phosphoenolpyruvate carboxylase in mistletoe leaves: Regulation of gene expression, protein content, and covalent modification.
abstract: Seasonal changes in the activity of phosphoenolpyruvate carboxylase (PEPCase, EC 4.1.1.31), a key enzyme in the interaction of carbohydrate and nitrogen metabolism, were studied in leaves of the C3 semiparasitic mistletoe, Viscum album, growing on different host trees. Maximum extractable PEPCase activities were higher in leaves of mistletoes growing on Betula pendula and Alnus glutinosa hosts compared with those on the conifers, Abies alba and Larix decidua. Independent of host, maximum extractable PEPCase activities were high in spring and autumn while low in summer. Samples with higher PEPCase activities showed higher amounts of PEPCase protein and higher PEPCase mRNA levels. A curvilinear correlation between leaf total nitrogen content and the maximum extractable PEPCase activity as well as PEPCase mRNA level suggested that nitrogen might affect the activity of PEPCase of mistletoe by up-regulating gene expression. In addition to extractable activity, seasonal changes of the PEPCase activation state, the ratio of activities resulting from limited:non-limited assays, were found, which was correlated to the variation of malate content in leaves of mistletoe. ATP-dependent activation of PEPCase was characterized by an increase in I0.5(L-malate), indicating that PEPCase of leaves of mistletoes is probably regulated via phosphorylation.
authors.affiliation: Lehrstuhl für Physiologische Ökologie der Pflanzen, Universität Tübingen, Auf der Morgenstelle 1, D-72076, Tübingen, Germany; Institut für Ökologie und Naturschutz, Universität Wien, Althanstr. 14, POB 285, A-1091 Wien, Austria; Albert-Ludwigs-Universität Freiburg, Institut für Forstbotanik und Baumphysiologie, Professur für Baumphysiologie, Am Flughafen 17, D-79110 Freiburg i. Br., Germany.
authors.forename: Xuemei
authors.initials: X
authors.lastname: Li
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wanek
authors.forename: U.
authors.initials: U
authors.lastname: Nehls
authors.forename: Marianne
authors.initials: M
authors.lastname: Popp
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Hampp
authors.forename: Heinz
authors.initials: H
authors.lastname: Rennenberg
authors.forename: Werner
authors.initials: W
authors.lastname: Einig