Storage and secretion processes in the spore of Gigaspora margarita Becker & Hall as revealed by high-pressure freezing and freeze substitution

Abstract

Spores of Gigaspora margarita Becker & Hall, an arbuscular mycorrhizal fungus, were cryofixed using high-pressure freezing and prepared for transmission electron microscopy by freeze substitution. The cryotechniques improved the ultrastructural preservation of the spore cytoplasm and revealed storage and secretion processes in the germinating spores of G. margarita. The storage structures in the bydrated and/or germinating spores bave been identified as belonging to three different classes: (i) lipid droplets limited by a membrane, (ii) protein-like bodies inside specialized vacuoles, and (ii) glycogen particles. During germ-tube differentiation, an abundant membranous system was observed. It consists of rougb ER, tubules and balloon-like Golgi equivalents, which produce vesicles associated with electron-dense granules. The granules seem to be incorporated info the wall. The results suggest that secretion and storage occur in tbe fungal spore during events comparable to those in yeasts or plant cells.