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Light and Electron Microscopic Study on the Mycorrhizae of Sporophytes of Botrychium virginianum - Arbuscular Structure Resembling Fossil Forms

Abstract:

The mycorrhizal structures of the sporophyte of the strictly protected fern Botrychium virginianum were studied by light and electron microscopy. The paper presented here is the first ultrastructural study of the mycorrhiza of the sporophyte of the genus Botrychium. The fungal colonization is restricted to two to three cell layers of the root cortex. The sometimes bifurcately ramifying hyphae form coils in the host cells. Single hypha arising from the coils penetrates into neighbouring cells and form arbuscules therein. The electron micrographs show high functional activity of the arbuscules, characterized by high glycogen-like content in the hyphae, a thin layer of filamentous matrix material in the interface between fungus and root cell, frequent cell organelles in the cytoplasm and lack of starch in the host cells containing arbuscules. The main distinctive feature of the mycorrhizae of Botrychium virginianum is the morphology of the arbuscules, which differs not only from the common fine-branched arbuscules, but also from the special structures reported previously from Ophioglossaceae. The robust, lobe-like branching arbuscules most resemble arbuscule structures found in Triassic fossils.