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

Spores of Gigaspora margarita Becker & Hall, an arbuscular mycorrbizal fungus, were cryofixed using bigbprcssure freezing and prepared for transmission electron microscopy by freeze substitution. I'hc cryotechniques improved tbe ultrastructural preservation of tbe spore cytoplasm and revealed storage and secretion processes in tbe germinating spores of G. margarita. The storage structures m the bydrated and/or germinating spores bave been identified as bflongtng to rhree differenr (-lasses: (i) lipid dropJeTs limited by a membrane, (ii) protein-like bodies inside specialized vacuoles, and (ii) ghcogen particles. During germ-tube differentiation, an abundant membranous system was obser\-ed. it consists of rougb KR. tubules and balloon-iike Golgi equivalents, wbicb produce vesicles associated witb electron-dense granules. Tbe granules seem (u be incorporated info the waU. The results suggest that secretion and storage occur in tbe fungal spore during events comparable to those in yeasts or plant cells.