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Plant Physiol, November 2000, Vol. 124, pp. 1381-1392
Glutathione and Homoglutathione Synthetases of Legume
Nodules. Cloning, Expression, and Subcellular
Localization1
Jose F.
Moran,
Iñaki
Iturbe-Ormaetxe,
Manuel A.
Matamoros,
Maria C.
Rubio,
Maria R.
Clemente,
Nicholas J.
Brewin, and
Manuel
Becana*
Departamento de Nutrición Vegetal, Estación
Experimental de Aula Dei, Consejo Superior de Investigaciones
Científicas, Apdo 202, 50080 Zaragoza, Spain (J.F.M., I.I.-O.,
M.A.M., M.C.R., M.R.C., M.B.); and Department of Genetics, John Innes
Centre, Norwich Research Park, Colney, Norwich NR4 7UH, United
Kingdom (I.I.-O., N.J.B.)
The thiol tripeptides glutathione (GSH) and
homoglutathione (hGSH) are very abundant in legume root nodules and
their synthesis is catalyzed by the enzymes -glutamylcysteine
synthetase ( ECS), GSH synthetase (GSHS), and hGSH synthetase
(hGSHS). As an essential step to elucidate the role of thiols in
N2 fixation we have isolated cDNAs encoding the three
enzymes and have quantified the transcripts in nodules. Assay of enzyme
activities in highly purified nodule organelles revealed that ECS is
localized in the plastids, hGSHS in the cytosol, and GSHS in the
cytosol and mitochondria. These results are consistent with sequence
analyses. Subcellular fractionation of nodules also showed that
bacteroids contain high thiol concentrations and high specific ECS
and GSHS activities. Results emphasize the role of nodule plastids in
antioxidant protection and in control of thiol synthesis, and suggest
that plastids may be important in the stress response of nodules.
Overall, our results provide further evidence that thiol synthesis is
critical for nodule functioning.
1
This work was supported by the Comisión
Interministerial de Ciencia y Tecnología and the European
Commission (grant nos. 2FD97-1101 and PB98-0522 to M.B.), by the
Dirección General de Enseñanza Superior e
Investigación Científica and the British Council
(Acción Hispano-Británica HB98-163 to M.B. and N.J.B.), by
a Marie Curie grant from the European Commission (to I.I.-O.), and by
the Biotechnology and Biological Sciences Research Council (to N.J.B.).
J.F.M., M.A.M., M.C.R., and M.R.C. were the recipients, respectively,
of a postdoctoral contract from the Ministry of Education and Culture
(Spain), a predoctoral fellowship from the Gobierno Vasco, and two
predoctoral fellowships from the Ministry of Education and Culture.
*
Corresponding author; e-mail becana{at}eead.csic.es; fax 34-
976-575620.
© 2000 American Society of Plant Physiologists
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