Ultrastructure of Ascus, Ascospore and Ascocarp in Neurospora lineolata

Abstract

Ascospores of N. lineolata develop from initials which are surrounded by a double membrane. The ascospore wall forms between the 2 membranes and consists at maturity of 3 components.sbd.a primary, thin and electron-transparent, a secondary thick, and a tertiary thin layer. The secondary rib-vein layer is made of electron-dense material in the costal and electron-transparent material in the intercostal regions. The germ pore is covered by the primary layer and situated in an intercostal area where the thickness of the secondary wall is greatly reduced. The protoplasm of the mature spore contains 1 or more nuclei and large lipid inclusions. The ascus wall appears essentially single layered. The apex of the ascus is characterized by a somewhat thickened wall which extends into a short cylinder or ring of wall-like material. The epiplasm of the ascus appears to vacuolate by dilations of cisternae of the endoplasmic reticulum. The ascocarp consists of 3 distinct layers. The 2 outer layers are richly endowed with lipid granules and other storage material, and also contain microbodies. The paraphyses remain throughout development but their walls drastically swell and fuse, thus filling the perithecial cavity with a mass of mucilageous material.