Immunological and Ultrastructural Demonstration of Nodulation of the European Alnus glutinosa (L.) Gaertn. Host Plant by an Actinomycetal Isolate from the North American Comptonia peregrina (L.) Coult. Root Nodule

The inoculation of the European Alnus glutinosa (L) Gaertn host plant by a pure culture of an actinomycete isolated from the North American Comptonia peregrina (L) Coult root nodule was successful. Fluorescein-labeled antibodies, specific against the actinomycetal isolate of the C peregrina root nodule, demonstrated the identity of this actinomycete in the resulting Alnus root nodules The nodulation process of this abnormal host-endophyte system was studied by light and electron microscopy The actinomycetal intruder was branched, and septate hyphae produced septate vesicles These endophyte vesicles were spherical like the Alnus-type instead of club shaped like the Comptonia-type The endophyte hyphae and vesicles were always encapsulated in a polysaccharide material surrounded by a host plasma-membrane envelope The Comptonia isolate, which forms spores in pure culture, did not sporulate inside the Alnus root nodule. In this abnormal host-endophyte system, appearance of the root nodules was delayed for 1-2 wk, compared with a normal Alnus-endophyte system However, the delayed root nodules which developed on all of the inoculated Alnus seedlings were effective in fixing nitrogen and were able to support satisfactory plant growth in a nitrogen-free medium.