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Plant Physiology Preview Published on November 5, 2008; 10.1104/pp.108.129940
Received September 16, 2008 ADP-Glucose pyrophosphorylase deficient pea embryos reveal specific transcriptional and metabolic changes of C:N metabolism and stress responses
Leibniz-Institut fur Pflanzengenetik und Kulturpflanzenforschung (IPK), D-06466 Gatersleben; Institute for Genome Research and Systems Biology (IGS), Center for Biotechnology (CeBiTec), Bielefeld University, D-33615 Bielefeld, Germany; Max-Planck-Institut fur Molekulare Pflanzenphysiologie, D-14476 Potsdam-Golm, Germany; Leibniz-Institut fur Pflanzenbiochemie, D-06120 Halle (Saale), Germany; Biology Department, Trent University, Peterborough, ON, K9J 7B8 Canada; Christian Albrechts University of Kiel, Institute of Botany, D-24098 Kiel, Germany * Corresponding author; email: weber{at}IPK-Gatersleben.de.
We present a comprehensive analysis of ADP-glucose pyrophosphorylase-repressed pea seeds using transcript and metabolite profiling to monitor effects that reduced carbon flow into starch has on C:N metabolism and related pathways. Changed patterns of transcripts and metabolites suggest that AGP-repression causes sugar accumulation and stimulates carbohydrate oxidation via glycolysis, tricarboxylic-acid cycle and mitochondrial respiration. Enhanced provision of precursors such as acetyl-CoA and organic acids apparently support other pathways and activates amino acid and storage protein biosynthesis, as well as pathways fed by cytosolic acetyl-CoA such as cysteine biosynthesis and fatty acid elongation/metabolism. As a consequence, the resulting higher N demand depletes transient N storage pools, specifically asparagine and arginine and leads to N limitation. Moreover, increased sugar accumulation appears to stimulate cytokinin-mediated cell proliferation pathways. In addition, the deregulation of starch biosynthesis resulted in indirect changes, such as increased mitochondrial metabolism and osmotic stress. The combined effect of these changes is an enhanced generation of reactive oxygen species (ROS) coupled with an upregulation of energy dissipating, ROS protection and defence genes. Transcriptional activation of MAP-kinase pathways and oxylipin synthesis indicate an additional activation of stress-signalling pathways. AGP-repressed embryos contain higher levels of jasmonate derivates; however, this increase is preferentially in non-active forms. The results suggest that, although, metabolic/osmotic alterations in iAGP pea-seeds result in multiple stress responses, pea seeds have effective mechanisms to circumvent stress-signalling under conditions, in which excessive stress response and/or cellular damage could prematurely initiate senescence or apoptosis.
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