FINE-STRUCTURE OF FRANKIA IN ROOT-NODULES AND ISOLATION OF FRANKIA FROM NODULES OF ACTINORHIZAL PLANTS GROWING IN JAPAN (REPRINTED FROM PLANT NUTRITION FOR SUSTAINABLE FOOD-PRODUCTION AND ENVIRONMENT, 1997)

We compared the fine structure and spatial arrangement of Frankia in r oot nodules of Alnus hirsta, Myrica ica rubra, Elaeagnus pungens, and Coriaria japonica by electron micrography and also isolated Frankia fr om nodules of Elaeagnus macrophylla and Alnus sieboldiana. Frankia in root nodules formed vesicles and hyphae but no sporangia. The diameter s of vesicles and hyphae were 2-3 mu m and 0.5-1.0 mu m, respectively. The shape and spatial arrangement of the vesicles in nodules varied a mong the species. The vesicles of A. hirsta and E. pungens were spheri cal and internally compartmentalized into multiple small segments by s epta, and those in M. rubra were spheroidal and internally septate. Th e vesicles of C. japonica were club-shaped and arranged peripherally a round a central vacuole and were not separated by septa. One strain fr om E. macrophylla and 13 strains from A. sieboldiana were isolated by a simple method of suspending the nodule homogenate directly in liquid Qmod medium, Hyphae, sporangia and vesicles which are morphological c haracteristics of Frankia were observed in the E. macrophylla isolate. However, only hyphae and sporangia were observed in the A. sieboldian a isolates. The E. macrophylla isolate formed nodules on the roots of the host plant. Eleven strains isolated from A. sieboldiana formed nod ules on the root of the host plants, but 2 strains did not cause nodul ation.