STORAGE AND SECRETION PROCESSES IN THE SPORE OF GIGASPORA-MARGARITA BECKER AND HALL AS REVEALED BY HIGH-PRESSURE FREEZING AND FREEZE-SUBSTITUTION

Spores of Gigaspora margarita Becker and Hall, an arbuscular mycorrhiz al fungus, were cryofixed using high-pressure freezing and prepared fo r transmission electron microscopy by freeze substitution. The cryotec hniques improved the ultrastructural preservation of the spore cytopla sm and revealed storage and secretion processes in the germinating spo res of G. margarita. The storage structures in the hydrated and/or ger minating spores have been identified as belonging to three different c lasses: (i) lipid droplets limited by a membrane, (ii) protein-like bo dies inside specialized vacuoles, and (ii) glycogen particles. During germ-tube differentiation, an abundant membranous system was observed. It consists of rough ER, tubules and balloon-like Golgi equivalents, which produce vesicles associated with electron-dense granules. The gr anules seem to be incorporated into the wall. The results suggest that secretion and storage occur in the fungal spore during events compara ble to those in yeasts or plant cells.