Fine Structure of Phialide and Conidiospore Development in Aspergillus giganteus ‘Wehmer’

The conidiophore vesicle is composed of a peripheral region which contains many nuclei and mitochondria and a central region which is densely packed with glycogen granules but contains very few organelles. The phialides, which arise as spherical protuberances from the surface of the vesicle, are bounded by a much thinner wall than that of the vesicle. Nuclei migrate into the phialides at a comparatively early stage in their development. Septa are present at the proximal ends of mature phialides and although pores are present in these septa it is suggested that they are too small to permit the ingress of such organelles as nuclei and mitochondria from the vesicle. The development of adjacent phialides is well synchronized but the development of the vesicle as a whole is not precisely co-ordinated. Each mature phialide contains a single nucleus, as do the conidiospores which they produce. The first conidiospore produced by a phialide arises as a spherical protrusion from the tapered, thickened apex of the phialide. The conidiospores are delimited from the phialide by the formation of a cross wall in a manner reminiscent of the process of septation in hyphae. When first formed the conidiospores have a cylindrical shape and they only assume their characteristic spherical shape at a later stage in development.