Ultrastructure of Ascus and Ascospore Development in Chaetomium brasiliense

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Abstract
Asci of C. brasiliense develop by the crozier method. Prior to ascospore delimitation, a typical ascus vesicle forms near the plasma membrane of the ascus. Membranes of the vesicle are similar to plasma membrane in width, leaflet asymmetry, and staining characteristics. The arrangement of membrane leaflets within the vesicle is consistent with an origin from invaginations of the ascus plasma membrane. Spindle pole bodies are adjacent to invaginations of the ascus vesicle and within unwalled ascospores; these bodies and associated microtubules are presumed to be involved in spore delimitation. Wall material forms between the spore-delimiting membranes and consists of an outer dense primary layer and an inner transparent secondary layer.