Ontogeny and fine structure of effective root nodules of the autumn olive (Elaeagnus umbellata)

Abstract

An ultrastructural study of effective root nodules of the autumn olive (Elaeagnus umbellata Thunb.) demonstrated the presence of hyphal and vesicular forms of the actinomycete endophyte. No sporangial forms of the endophyte were observed within these nodules. The hyphae contained septa, prominent nucleoid regions, and many ribosomes. The endophytic vesicles were initially nonseptate and then became multichambered as a result of the inward growth of complete and incomplete septa. Glycogen particles were numerous in nonseptate and early stages of septate endophytic vesicle formation and in adjacent hyphae but were absent in more developed stages of septate endophytic vesicles. The endophytic vesicles also contained prominent nucleoid areas, vesicular mesosomes, and crystalline-like striated bodies. A capsule, probably derived from host Golgi cisternae and profiles of dilated rough endoplasmic reticulum, surrounded both forms of the endophyte. The endophytic vesicle cell walls consisted of an outer layer continuous with the hyphal cell wall, a middle clear area or “void space,” and an electron-dense inner layer. The “void space” of the endophyte cell wall was resolved into many thin laminae by freeze–fracture microscopy. The laminae were presumed to be different from the outermost cell wall layer because they were washed out in the solvents used in preparing specimens for the TEM.