Ultrastructure of Mycorrhizas of Dracophyllum secundum R. Br. (Ericales:Epacridaceae)

Abstract

Dracophyllum secundum R. Br. (Epacridaceae) often possessed ericoid mycorrhizas; fungal endophytes formed coils within cells of the epidermis of hair-roots. The plant plasma membrane extended around the hyphae. In some epidermal cells of hair-roots, both plant and fungal cells retained their structural integrity, both partners showing mitochondrial, vacuolar and lipid droplet profiles, and with much of the plant cytoplasm associated with the hyphal coils. In other epidermal cells of hair-roots, fungal coils were present but cytoplasmic features of both symbionts appeared to have broken down. Some epidermal cells showed no evidence of fungal infection. These three arrangements could occur in root-cells of the same age, and are interpreted as resulting from different stages in the development and degeneration of the infection by the mycorrhizal fungus. Two structural types of fungal endophyte here found in ericoid mycorrhizas in D. secundum: one with simple septa, Woronin bodies and two-layered walls (presumed to be an Ascomycete), and another with dolipore septa with imperforate parenthesomes (presumed to be a Basidiomycete). The possibilities that the mycorrhizas may be seasonal, and that mycorrhizal status varies from place to place, are discussed.