Ultrastructure of basidiospores of the mycorrhizal fungus Pisolithus tinctorius

Abstract

Basidia of Pisolithus tinctorius develop from terminal hyphal cells. The distal portion of the basidium enlarges, meiosis occurs, and basidiospore initials develop on short, stout, sterigmata, Young basidia and basidiospore initials are embedded in a fibrillar matrix. As spore initials develop, the basidium becomes highly vacuolate as the contents of the basidium move into the spore initials. A single nucleus typically enters each spore initial. A spore initial is eventually delimited from the basidium near the distal end of the sterigma. Wall material is subsequently deposited in this region sealing off the young spore from the basidium. The basidium then collapses leaving the short sterigma attached to the spore. Young basidiospores are initially highly vacuolate but a large lipid droplet eventually develops and displaces the other cellular components to the periphery of the spore. The oldest spores examined possessed a four-layered wall, the outer layer of which bears the surface spines. Many aberrant spores possessing more or less typical surface spines but lacking cellular components were routinely observed in this study side by side with normal spores.