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Photorespiratory Metabolism and Nodule Function: Behavior of Lotus japonicus Mutants Deficient in Plastid Glutamine Synthetase

February 2012 , Volume 25 , Number  2
Pages  211 - 219

Margarita García-Calderón,1 Maurizio Chiurazzi,2 M. Rosario Espuny,3 and Antonio J. Márquez1

1Departamento de Bioquímica Vegetal y Biología Molecular, Universidad de Sevilla, C/ Profesor García González 1, 41012 Sevilla, Spain; 2Institute of Genetics and Biophysics A. Buzzati Traverso, Via Pietro Castellino, 111–80131, Napoli, Italy; 3Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla, Avda. Reina Mercedes 6, 41012-Sevilla, Spain

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Accepted 11 October 2011.

Two photorespiratory mutants of Lotus japonicus deficient in plastid glutamine synthetase (GS2) were examined for their capacity to establish symbiotic association with Mesorhizobium loti bacteria. Biosynthetic glutamine synthetase (GS) activity was reduced by around 40% in crude nodule extracts from mutant plants as compared with the wild type (WT). Western blot analysis further confirmed the lack of GS2 polypeptide in mutant nodules. The decrease in GS activity affected the nodular carbon metabolism under high CO2 (suppressed photorespiration) conditions, although mutant plants were able to form nodules and fix atmospheric nitrogen. However, when WT and mutant plants were transferred to an ordinary air atmosphere (photorespiratory active conditions) the nodulation process and nitrogen fixation were substantially affected, particularly in mutant plants. The number and fresh weight of mutant nodules as well as acetylene reduction activity showed a strong inhibition compared with WT plants. Optical microscopy studies from mutant plant nodules revealed the anticipated senescence phenotype linked to an important reduction in starch and sucrose levels. These results show that, in Lotus japonicus, photorespiration and, particularly, GS2 deficiency result in profound limitations in carbon metabolism that affect the nodulation process and nitrogen fixation.

© 2012 The American Phytopathological Society