Ultrastructure of the ascus apical apparatus and ascospore wall in Ombrophila hemiamyloidea (Helotiales, Ascomycota)
Verkley, Gerard J.M.
The ultrastructure of the ascus apical apparatus, lateral ascus wall and ascospore wall of Ombrophila hemiamyloidea was studied with TEM. The apical apparatus is composed of a well-developed apical thickening that surrounds an apical chamber and is fully occupied by a broad annulus. This annulus initially consists of a homogeneous matrix, but, due to changes in ultrastructure and PA-TCH-SP reactivity, two annular subregions become distinguishable as the ascus matures. These features do not correlate with the hemiamyloid properties of the annulus in Lugol's iodine solution, which imparts a distinct and homogeneous red colour to both of these subregions in mature asci. After dehiscence, the annulus is everted over an angle of about 90°. The mature ascospore wall is composed of an endospore covered by an epispore. The endospore is lined by an inner wall layer which is continuous with the septal walls. Comparison with ultrastructure of the ascus and ascospores of Ombrophila violacea, the type species of the genus Ombrophila, indicates that O. hemiamyloidea does not belong in this genus. The general morphology of the apical apparatus and the structure and reactivity of the annulus agree with the Pezicula ascus type. The results indicate that O. hemiamyloidea is more closely related to Pezicula and related genera of the family Dermateaceae than to the Vibrisseaceae or the Mollisiaceae as previously been suggested.