Particle density and protein composition of the peribacteroid membrane from soybean root nodules is affected by mutation in the microsymbiont Bradyrhizobium japonicum

Abstract

Particle frequency of the peribacteroid membrane (PBM) from nodules of Glycine max (L.) Merr. cv. Maple Arrow infected with Bradyrhizobium japonicum 61-A-101 (wild-type strain) was determined by freeze-fracturing to be about 2200·μm(-2) in the protoplasmic fracture face and 700·μm(-2) in the exoplasmic fracture face. In membranes isolated from nodules infected with the mutant RH 31-Marburg of B. japonicum, the particle frequency was similar in both fracture faces with 1200-1300 particles·μm(-2). Analysis of particlesize distribution on peribacteroid membranes showed a loss, especially of particle sizes larger than 11 nm, in the mutant-infected nodules. Two-dimensional gel electrophoresis (isoelectric focussing and sodium dodecyl sulfate-polyacrylamide) showed 27 different polypeptides in the PBM from nodules infected with the wild-type strain, four of which were absent from the PBM of nodules infected with the mutant RH 31-Marburg, which also exhibited one extra small-molecular-weight polypeptide. At least 14 of the 27 polypeptides in the PBM from the wild-type-infected nodule were glycoproteins. In three of these glycoproteins, post-translational modifications were either lacking or different when the membrane was derived from mutant-infected nodules.