Ultrastructure of Actinorhizal Nodules of Cowania subintegra (Rosaceae)

Abstract

The structure of actinorhizal nodules of Cowania subintegra (common name: Arizona cliffrose) was studied by transmission electron microscopy. Morphological forms of the actinomycete in host cortical cells included septate hyphae and nonseptate elliptically shaped vesicles. Vesicles were distributed randomly throughout the host cytoplasm and were surrounded by host plasma membrane. No sporangia were observed in these nodules. Both endophytic hyphae and endophytic vesicles contained nucleoid regions, vesicular mesosomes, and rosette-shaped granules. The fine structure of the microsymbiont was similar to that found in other Frankia-induced root nodules, especially those in other members of the Rosaceae.