PLANT PHYSIOLOGY , Vol 115, Issue 4 1329-1340, Copyright © 1997 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
The Aberrant Cell Walls of Boron-Deficient Bean Root Nodules Have No Covalently Bound Hydroxyproline-/Proline-Rich Proteins
I. Bonilla, C. Mergold-Villasenor, M. E. Campos, N. Sanchez, H. Perez, L. Lopez, L. Castrejon, F. Sanchez and G. I. Cassab
Departamento de Biologia, Facultad de Ciencias, Universidad Autonoma de Madrid, 28094 Madrid, Spain (I.B.)
B-deficient bean (Phaseolus vulgaris L.) nodules examined by light
microscopy showed dramatic anatomical changes, mainly in the parenchyma
region. Western analysis of total nodule extracts examined by sodium
dodecyl sulfate-polyacrylamide gel electrophoresis showed that one 116-kD
polypeptide was recognized by antibodies raised against hydroxyproline-rich
glycoproteins (HRGPs) from the soybean (Glycine max) seed coat. A protein
with a comparable molecular mass of 116 kD was purified from the cell walls
of soybean root nodules. The amino acid composition of this protein is
similar to the early nodulin (ENOD2) gene. Immunoprecipitation of the
soybean ENOD2 in vitro translation product showed that the soybean seed
coat anti-HRGP antibodies recognized this early nodulin. Furthermore, we
used these antibodies to localize the ENOD2 homolog in bean nodules.
Immunocytochemistry revealed that in B-deficient nodules ENOD2 was absent
in the walls of the nodule parenchyma. The absence of ENOD2 in B-deficient
nodules was corroborated by performing hydroxyproline assays. Northern
analysis showed that ENOD2 mRNA is present in B-deficient nodules;
therefore, the accumulation of ENOD2 is not affected by B deficiency, but
its assembly into the cell wall is. B-deficient nodules fix much less N2
than control nodules, probably because the nodule parenchyma is no longer
an effective O2 barrier.
