PLANT PHYSIOLOGY , Vol 110, Issue 4 1249-1256, Copyright © 1996 by American Society of Plant Biologists
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PLANT-MICROBE AND PLANT-INSECT INTERACTIONS |
Effects of Boron on Rhizobium-Legume Cell-Surface Interactions and Nodule Development
L. Bolanos, N. J. Brewin and I. Bonilla
Departamento de Biologia, Facultad de Ciencias, Universidad Autonoma de Madrid, 28049 Madrid, Spain (L.B., I.B.)
Boron (B) is an essential micronutrient for the development of
nitrogen-fixing root nodules in pea (Pisum sativum). By using monoclonal
antibodies that recognize specific glycoconjugate components implicated in
legume root-nodule development, we investigated the effects of low B on the
formation of infection threads and the colonization of pea nodules by
Rhizobium leguminosarum bv viciae. In B-deficient nodules the proportion of
infected host cells was much lower than in nodules from plants supplied
with normal quantities of B. Moreover, the host cells often developed
enlarged and abnormally shaped infection threads that frequently burst,
releasing bacteria into damaged host cells. There was also an
over-production of plant matrix material in which the rhizobial cells were
embedded during their progression through the infection thread.
Furthermore, in a series of in vitro binding studies, we demonstrated that
the presence of B can change the affinity with which the bacterial cell
surface interacts with the peribacteroid membrane glycocalyx relative to
its interaction with intercellular plant matrix glycoprotein. From these
observations we suggest that B plays an important role in mediating
cell-surface interactions that lead to endocytosis of rhizobia by host
cells and hence to the correct establishment of the symbiosis between pea
and Rhizobium.
