Ultrastructure of teliospore germination and basidiospore formation in the rust fungus Gymnosporangium clavipes

Abstract

A mature teliospore of Gymnosporangium clavipes is two celled with a long pedicel. The spore wall appears multilayered and a germ pore region is present in the wall at each end of the teliospore. The cytoplasm of the spore is dense and packed with lipid droplets. A single, dense, prophase nucleus is present in each cell. Synaptonemal complexes were observed in younger spores but not in mature, germinable spores. The cytoplasm of a germinating spore appears less dense than that of a nongerminating spore. During germination a germ tube emerges from the germ pore region of each cell. Cytoplasmic vesicles are numerous in the tip of the rapidly elongating promycelium. The nucleus enters the promycelium and divides meiotically. Centripetally developing septa divide the promycelium into four uninucleate cells each of which gives rise to a sterigma at the tip of which a basidiospore initial develops. Cytoplasmic vesicles are prominent in the tip of the developing sterigma and in the basidiospore initial. Once the nucleus has entered the basidiospore initial it divides mitotically. During this time time a septum develops within the sterigma and the spore is delimited from the sterigma by the formation of a second septum at the base of the spore.