Morphogenesis and Fine Structure of the Actinomycetous Endophyte of Nitrogen-Fixing Root Nodules of Comptonia peregrina

Abstract

The morphogenesis and fine structure of the cultured endophyte isolated from root nodules of Comptonia peregrina have been studied, utilizing scanning electron microscopy, transmission electron microscopy, and Nomarski interference microscopy; comparisons were made with the endophyte in vivo The actinomycetous nature of the endophyte was confirmed Prokaryotic, branched septate hyphae, less than 1 μm in diameter, are the predominant growth form Some hyphae increase in diameter (ca. 1-1.5 μm) and undergo morphogenesis, forming club-shaped sporangia in vitro The sporangia produced numerous sporangiospores which are presumed to be the propagative state of the microorganism. Sporangia were formed by the growth of longitudinally and transversely oriented septa which compartmentalize the wider hyphae. Sporangia were not observed in vivo in Comptonia Club-shaped septate vesicles formed in vivo but not in vitro. The mature spores contained electron-dense inclusions resembling eukaryotic nucleoli, numerous vesicular structures, nucleoid regions, and a thick multilayered wall. The microorganism in vitro lacked a capsule which the organism possessed in vivo, providing further evidence for the role of the host in the deposition of this encapsulating wall material.