Ultrastructural observations on septal and merosporangial ontogeny in Linderina pennispora (Kickxellales; Zygomycetes)

Abstract

Septal ontogeny in Linderina pennispora Raper & Fennell is initiated by the ingrowth of material from the inner of the two layers of the cell wall. The growing point of the septum bifurcates and continues growth, forming a lenticular cavity into which the septal plug is deposited. This type of septal development occurs in all septa except those produced between the pseudophialides and the merosporangia and spores. The latter septal type initially is formed as previously described, but then additional wall material is produced both above and below the septum. In the merosporangiospore three layers of wall material are produced, the inner two layers give rise to the spore spines, and at maturity all wall layers coalesce and form a single, thick spore wall. Extra wall material in the apex of the pseudophialide gives rise to a multilobed and mottled vacuole that shrivels just before spore liberation. Mature merosporangiospores are the only structures with spore spines. Aerial spines are produced on all structures except the merosporangiospores, although a relatively larger number of the aerial spines are produced on the aerial hyphae than on the pseudophialides and the sporocladia. The possible functions of the spore spines and the aerial spines are discussed.