Host Influence on the Ultrastructure of Root Nodules of Lupinus luteus and Ornithopus Sativus

SUMMARY: The ultrastructure of Lupinus luteus L. and Ornithopus sativus Brot. root nodules derived from infection by Rhizobium lupini strain D25 was examined. In both cases the associations produced completely effective nodules but their gross morphology was markedly different. Bacteria within the O. sativus nodules were enclosed in groups by a membranous envelope, and the bacteria had electron translucent regions. Bacteria within the L. luteus nodules were enclosed singly and did not exhibit similar electron translucent regions. Starch granules were observed within infected cells of L. luteus but not within uninfected cells; the reverse was observed in O. sativus cells.