Ultrastructure of the Alnus crispa var. mollis Fern. root nodule endophyte

Abstract

Nitrogen-fixing, field-obtained root nodules of the silky green alder were studied by transmission electron microscopy. The nodule endophyte exhibited a prokaryotic cytology and was present in two forms: the hypha (0.3–1.0 μm), which was branched and septate, and the vesicle (3–5 μm), which was also septate and developed at the parental hypha tip. Bacteria-like cells, previously observed in light microscopy studies, were not seen in the present work. The actinomycete-like endophyte penetrated through the host cell wall and became enveloped by a capsular material (0.1 μm), the whole being enclosed by host membranes. In some host cells, the endophyte appeared to lyse and become a mass of shrunken debris. The fine structure of the Alnus crispa var. mollis root nodule endophyte was found to be similar to that of other non-leguminous root nodule endophytes.