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Effects of Soybean Mosaic Virus Infection on Ultrastructure of Bacteroidal Cells in Soybean Root Nodules. J. C. Tu, Biological Sciences Electron Microscope Laboratory, University of Alberta, Edmonton, Alberta, Canada T6G 2E9; Phytopathology 67:199-205. Accepted for publication 15 September 1976. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-199.

Differences between the rhizobial bacteroids (Rhizobium japonicum) in situ in the bacteroidal cells of root nodules in healthy and in soybean mosaic virus (SMV)- infected soybean plants (Glycine max) were investigated using thin-sectioning and freeze-fracturing techniques. The bacteroids in SMV-infected cells differed significantly from those in healthy cells. These differences were evident in both the initial stage and, to a lesser degree, in the intermediate stage of bacteroid development. In the advanced stage of bacteroid development, differences between bacteroids in healthy and in SMV-infected cells were no longer apparent. Differences in bacteroidal cells in SMV-infected versus healthy plants include (i) a decrease in endocytotic and exocytotic vesiculation on the membrane envelope of the bacteroids and on the plasma membrane of bacteroidal cells, (ii) a decrease in number of vesicles in the space between the bacteroid and the membrane envelope, and (iii) a decrease in the space between the bacteroid and the membrane envelope. The possible significance of these changes relative to the decreased efficiency of N2-fixation is discussed.