Ultrastructural observations onNimbospora bipolaris(Halosphaeriaceae, Ascomycetes)

Abstract

The ultrastructure of the ascus, ascospores and appendages ofNimbospora bipolariswere examined at the transmission electron microscope level. The mature ascus wall comprises a single narrow electron-opaque layer which deliquesces and lacks an apical elaboration. Ascospore walls comprise a bipartite mesosporium, a thinner electron-opaque episporium and an outer mucilaginous sheath. Before release from the ascus the mucilaginous sheath is compact and folded. The fibrillar, trailing ascospore appendages are arranged in eight equidistant tufts around the circumference of the septum, originate from the mesosporium and emerge through pores in the episporium. In early stages of development the appendages are retained within the mucilaginous sheath but upon release from the ascus the sheath expands and the appendages pierce the sheath and radiate out to form their characteristic appearance. Ascospore ontogeny inN. bipolarisis compared with other appendaged members of the Halosphaeriaceae.