Ligands of boron in Pisum sativum nodules are involved in regulation of oxygen concentration and rhizobial infection.
Boron (B) is an essential nutrient for N(2)-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.
Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Darwin 2, 28049-Madrid, Spain.
María
M
Reguera
Monika
M
Wimmer
Pilar
P
Bustos
Heiner E
HE
Goldbach
Luis
L
Bolaños
Ildefonso
I
Bonilla
D060387:Ascorbate Peroxidases; D001895:Boron / Q000172:deficiency / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D018506:Gene Expression Regulation, Plant; D008024:Ligands; D010100:Oxygen / Q000378:metabolism*; D018532:Pisum sativum / Q000201:enzymology / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology*; D010544:Peroxidases / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016961:Rhizobium leguminosarum / Q000502:physiology*; D053204:Root Nodules, Plant / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology*; D013347:Subcellular Fractions / Q000378:metabolism
D008024:Ligands; D018749:RNA, Plant; D010544:Peroxidases; D060387:Ascorbate Peroxidases; D001895:Boron; D010100:Oxygen