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Metabolite effectors for short‐term nitrogen‐dependent enhancement of phosphoenolpyruvate carboxylase activity and decrease of net sucrose synthesis in wheat leaves
Author(s) -
Manh Cao Thi,
Bismuth Evelyne,
Boutin JeanPierre,
Provot Madeleine,
Champigny MarieLouise
Publication year - 1993
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1993.tb05199.x
Subject(s) - phosphoenolpyruvate carboxylase , biochemistry , glutamate synthase , glutamine , pyruvate carboxylase , phosphoenolpyruvate carboxykinase , azaserine , glutamine synthetase , biology , sucrose , chemistry , enzyme , amino acid
We have shown that feeding 40 m M NO − 3 in the light to N‐limited detached leaves from wheat ( Triticum aestivum L. cv Fidel) results in the short‐term, in the enhancement of light‐dependent phosphoenolpyruvate carboxylase (PEPcase) activation and the decrease of net sucrose synthesis. The aim of the research was to determine specifically the N metabolite(s) responsible for this modulation. Detached leaves from wheat were fed for 90 min in the light with (1) NO − 3 , NH + 4 , glutamine, glutamate, alanine or aspartate; or (2) NO − 3 supplemented with sodium tungstate, methionine sulfoximine, azaserine or amino oxyacetate in order to inhibit specifically nitrate reductase, glutamine synthetase, glutamate synthase or amino transferases. Changes in phosphoenol‐pyruvate carboxylase activity and net sucrose synthesis were measured at the end of each treatment. Both sodium tungstate and methionine sulfoximine which inhibit reduction of NO − 3 and assimilation of NH + 4 respectively, suppressed the NO − 3 ‐dependent activation of phosphenolpyruvate carboxylase. Tungstate restored the rate of sucrose synthesis to the level of the control (absence of nitrate), while methionine sulfoximine enhanced it. Whatever way the glutamine level was increased in tissues (feeding the leaves with glutamine or with azaserine which inhibits glutamate synthase), enhancement of the light‐dependent activation of phosphoenolpyruvate carboxylase and reduction of sucrose synthesis were observed similar to feeding the leaves with NO − 3 . In contrast, glutamate and aspartate suppressed light dependent phosphoenolpyruvate carboxylase activation. These results indicate that glutamine is the most likely effector for controlling the N‐dependent activation of phosphoenolpyruvate carboxylase, and that the glutamine/glutamate ratio might regulate phosphoenolpyruvate carboxylase activation and the rate of sucrose synthesis in wheat leaves. Glutamine and glutamate were shown to be positive and negative effectors respectively of in vitro PEPcase‐protein kinase. In addition glutamine and glutamate were shown to control PEPcase by induction and repression of RNA synthesis respectively. Thus, two aspects of PEPcase modulation by these metabolites must be considered, (1) control of the PEPcase gene expression and (2) regulation of the PEPcase‐protein kinase.