Cytology and development of a mycorrhiza‐like infection in the gametophyte of Conocephalum conicum (L.) Dum. (Marchantiales, Hepatophyta)

Abstract

An aseptate fungus associated with the gametophyte of the hepatic Conocephalum conicum (L.) Dum. was studied by light and electron microscopy. The fungus forms a highly branched mycelium external to the plant. Fungal hyphae colonize the smooth‐walled rhizoids, through which they pass into the gametophyte parenchyma of the midrib. The fungus in the parenchyma is entirely intracellular. Vesicles are found in rhizoids and a few ventral layers of parenchyma cells. Prominent arbuscules develop in more internal cells from lateral branches of infecting hyphae that spread from cell to cell. Infected host cells show cytoplasmic proliferation, especially of ribosomes, Plastids and mitochondria, The arbuscules eventually degenerate leaving clumps of collapsed hyphae. Reinfection of cells with degenerate arbuscules was not observed. The ultrastructural and developmental characteristics of the fungus and its high cytological compatibility with the host are indicative of a well integrated symbiotic association similar to the vesicular–arbuscular mycorrhizas of higher plants. Copyright © 1989, Wiley Blackwell. All rights reserved