Fine Structure of Phialide and Conidiospore Development in Aspergillus giganteus 'Wehmer'

The conidiophore vesicle is composed of a peripheral regionwhich contains many nuclei and mitochondria and a central regionwhich is densely packed with glycogen granules but containsvery few organelles. The phialides, which arise as sphericalprotuberances from the surface of the vesicle, are bounded bya much thinner wall than that of the vesicle. Nuclei migrateinto the phialides at a comparatively early stage in their development.Septa are present at the proximal ends of mature phialides andalthough pores are present in these septa it is suggested thatthey are too small to permit the ingress of such organellesas nuclei and mitochondria from the vesicle. The developmentof adjacent phialides is well synchronized but the developmentof the vesicle as a whole is not precisely co-ordinated. Eachmature phialide contains a single nucleus, as do the conidiosporeswhich they produce. The first conidiospore produced by a phialidearises as a spherical protrusion from the tapered, thickenedapex of the phialide. The conidiospores are delimited from thephialide by the formation of a cross wall in a manner reminiscentof the process of septation in hyphae. When first formed theconidiospores have a cylindrical shape and they only assumetheir characteristic spherical shape at a later stage in development.