ENDOPHYTE DIFFERENTIATION IN CASUARINA ACTINORHIZAE

This is an ultrastructural study of development of infected cells in nitrogen fixing root nodules of Casuarina spp. While several aspects of development are similar to those found in many other actinorhizae, unusual aspects of development of the host cell and differentiation of the endophyte in Casuarina are correlated with unusual changes in the wall of the infected cell. Instead of vesicles the endophyte forms atypical hyphae in mature infected cells. These unusual hyphal forms are termed intracellular hyphae. Intracellular hyphae are nonseptate hyphae which originate and terminate within the same host cell, and have a varying diameter and a multidirectional growth and branching pattern. A laminate surface layer previously undescribed on hyphae of Frankia is a feature common to most Casuarina endophytic hyphae and is probably similar chemically to the laminae comprising the multilamellate envelope of endophytic vesicles in other actinorhizae.