Ligands of boron in Pisum sativum nodules are involved in regulation of oxygen concentration and rhizobial infection

Authors

  • MARÍA REGUERA,

    1. Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Darwin 2, 28049-Madrid, Spain,
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  • MONIKA WIMMER,

    1. Institute of Crop Science and Resource Conservation – Plant Nutrition, University of Bonn, Karlrobert-Kreiten-Strasse 13, D–53115 Bonn, Germany and
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  • PILAR BUSTOS,

    1. Departamento de Nutrición Vegetal, Estación Experimental de Aula Dei, Consejo Superior de Investigaciones Científicas, Apartado 13034, 50080 Zaragoza, Spain
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  • HEINER E. GOLDBACH,

    1. Institute of Crop Science and Resource Conservation – Plant Nutrition, University of Bonn, Karlrobert-Kreiten-Strasse 13, D–53115 Bonn, Germany and
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  • LUIS BOLAÑOS,

    Corresponding author
    1. Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Darwin 2, 28049-Madrid, Spain,
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  • ILDEFONSO BONILLA

    1. Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Darwin 2, 28049-Madrid, Spain,
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L. Bolaños. Fax: +34913978344; e-mail: luis.bolarios@uam.es

ABSTRACT

Boron (B) is an essential nutrient for N2-fixing legume–rhizobia symbioses, and the capacity of borate ions to bind and stabilize biomolecules is the basis of any B function. We used a borate-binding-specific resin and immunostaining techniques to identify B ligands important for the development of Pisum sativum–Rhizobium leguminosarum 3841 symbiotic nodules. arabinogalactan–extensin (AGPE), recognized by MAC 265 antibody, appeared heavily bound to the resin in extracts derived from B-sufficient, but not from B-deficient nodules. MAC 265 stained the infection threads and the extracellular matrix of cortical cells involved in the oxygen diffusion barrier. In B-deprived nodules, immunolocalization of MAC 265 antigens was significantly reduced. Leghaemoglobin (Lb) concentration largely decreased in B-deficient nodules. The absence of MAC 203 antigens in B-deficient nodules suggests a high internal oxygen concentration, as this antibody detects an epitope on the lipopolysaccharide (LPS) of bacteroids typically expressed in micro-aerobically grown R. leguminosarum 3841. However, B-deprived nodules did not accumulate oxidized lipids and proteins, and revealed a decrease in the activity of the major antioxidant enzyme ascorbate peroxidase (APX). Therefore, B deficiency reduced the stability of nodule macromolecules important for rhizobial infection, and for regulation of oxygen concentration, resulting in non-functional nodules, but did not appear to induce oxidative damage in low-B nodules.

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