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Published on April 25, 2008; 10.1104/pp.108.117408

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Received February 6, 2008
Accepted April 22, 2008

Knocking Out Cytosolic Cysteine Synthesis Compromises the Antioxidant Capacity of the Cytosol to Maintain Discrete Concentrations of Hydrogen Peroxide in Arabidopsis

M. Carmen Lopez-Martin , Manuel Becana , Luis C. Romero , and Cecilia Gotor *

Instituto de Bioquimica Vegetal y Fotosintesis, Consejo Superior de Investigaciones Cientificas and Universidad de Sevilla, Avda. Americo Vespucio, 49, 41092 Sevilla, Spain; Departamento de Nutricion Vegetal, Estacion Experimental de Aula Dei, Consejo Superior de Investigaciones Cientificas, Apartado 202, 50080 Zaragoza, Spain

* Corresponding author; email: gotor{at}ibvf.csic.es.

Plant cells contain different O-acetylserine(thiol)lyase (OASTL) enzymes involved in Cys biosynthesis and located in different subcellular compartments. These enzymes are made up of a complex variety of isoforms resulting in different subcellular Cys pools. To unravel the contribution of cytosolic Cys to plant metabolism, we characterized the knockout oas-a1.1 and osa-a1.2 mutants, deficient in the most abundant cytosolic OASTL isoform in Arabidposis thaliana. Total intracellular Cys and glutathione concentrations were reduced, and the glutathione redox state was shifted in favour of its oxidized form. Interestingly, the capability of the mutants to chelate heavy metals did not differ from that of the wild type, but the mutants have an enhanced sensitivity to Cd. With the aim of establishing the metabolic network most influenced by the cytosolic Cys pool, we used the ATH1 GeneChip for evaluation of differentially expressed genes in the oas-a1.1 mutant grown under non-stress conditions. The transcriptomic footprints of mutant plants had predicted functions associated with various physiological responses that are dependent on reactive oxygen species and suggested that the mutant was oxidatively stressed. Evidences that the mutation caused a perturbation in H2O2 homeostasis are that in the knockout, H2O2 production was localized in shoots and roots; spontaneous cell death lesions occurred in the leaves; and lignification and guaiacol peroxidase activity were significantly increased. All these findings indicate that a deficiency of OAS-A1 in the cytosol promotes a perturbation in H2O2 homeostasis and that Cys is an important determinant of the antioxidative capacity of the cytosol in Arabidopsis.






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