Open AccessNitrate Activation of Cytosolic Protein Kinases Diverts Photosynthetic Carbon from Sucrose to Amino Acid Biosynthesis
Author(s) -
MarieLouise Champigny,
Christine H. Foyer
Publication year - 1992
Publication title -
plant physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.554
H-Index - 312
eISSN - 1532-2548
pISSN - 0032-0889
DOI - 10.1104/pp.100.1.7
Subject(s) - biochemistry , sucrose , amino acid synthesis , phosphoenolpyruvate carboxylase , sucrose phosphate synthase , cytosol , phosphoenolpyruvate carboxykinase , biosynthesis , amino acid , enzyme , pyruvate carboxylase , photosynthesis , protein phosphorylation , metabolism , biology , chemistry , sucrose synthase , protein kinase a , lysine , invertase
The regulation of carbon partitioning between carbohydrates (principally sucrose) and amino acids has been only poorly characterized in higher plants. The hypothesis that the pathway of sucrose and amino acid biosynthesis compete for carbon skeletons and energy is widely accepted. In this review, we suggest a mechanism involving the regulation of cytosolic protein kinases whereby the flow of carbon is regulated at the level of partitioning between the pathways of carbohydrate and nitrogen metabolism via the covalent modulation of component enzymes. The addition of nitrate to wheat seedlings (Triticum aestivum) grown in the absence of exogenous nitrogen has a dramatic, if transient, impact on sucrose formation and on the activities of sucrose phosphate synthase (which is inactivated) and phosphoenolpyruvate carboxylase (which is activated). The activities of these two enzymes are modulated by protein phosphorylation in response to the addition of nitrate, but they respond in an inverse fashion. Sucrose phosphate synthase in inactivated and phosphoenolpyruvate carboxylase is activated. Nitrate functions as a signal metabolite activating the cytosolic protein kinase, thereby modulating the activities of at least two of the key enzymes in assimilate partitioning and redirecting the flow of carbon away from sucrose biosynthesis toward amino acid synthesis.