Teliospores of Entorrhiza casparyana (Ustilaginales): a correlated thin-sectioning and freeze–fracture study of endogenously dormant spores

Abstract

A correlated thin-sectioning and freeze–fracturing approach was used to reveal the ultrastructure of endogenously dormant teliospores in the smut fungus Entorrhiza casparyana (Magn.) Lagerh. Conventional fixation and embedding methods yielded poor preservation of the wall and protoplasm. Successful preservation was achieved by fixing frozen and cryosectioned spores in glutaraldehyde and subsequently processing by standard procedures for transmission electron microscopy. Freeze–fracturing provided cross- and contour-fractured views of the protoplasm and the different layers of the wall. The wall is thick, consisting of three main layers: outer, middle, and inner, with the outer and inner layers further differentiated into zones. The warty zone dominates the outer layer and consists of radial protuberances (warts) with the regions between filled to varying degrees with similar wall material containing electron-transparent lamellae. The extent of differentiation of the warty zone is reflected in the surface morphology of the spores, which ranges from verrucose to almost smooth. At the base of the outer layer is an electron-translucent irregular zone. The middle and inner layers are regular in thickness around the spore, with the middle layer being the most electron dense. The inner layer is differentiated into three zones. The most distinctive is zone 2 which in freeze–fractured walls has an unique mosaic of striae. Cytochemical staining of the wall for polysaccharide material gives a positive reaction only for the warty zone. The protoplasm contains a single nucleus and is dominated by numerous spheroidal storage lipid bodies. Squeezed among the lipid bodies are organelles, believed to be microbodies, containing a granular matrix and often electron-transparent areas. These organelles failed to show catalase activity with the 3,3′-diaminobenzidine method. Occasional short profiles of endoplasmic reticulum cisternae, a few mitochondria with sparse cristae, dispersed small clusters of glycogen, and sometimes scattered ribosomes are also present in the cytoplasm. All these features are typical of dormant spores with a low metabolic activity.

Ultrastructure of developing basidiospores in Rhizopogon roseolus (= R. rubescens)

“…During maturation, lipid bodies formed and expanded, and the spore walls became electron dense and multilayered. High lipid content is a feature of most mushroom spores that have been studied ultrastructurally (Voelz and Niederpruem 1964;Manocha 1965;Hyde and Walkinshaw 1966;Stock and Hess 1970;Heintz and Niederpruem 1971;Nakai and Ushiyama 1974b;Greuter and Rast 1975;Arita 1979;Fineran and Fineran 1984;Ruch and Motta 1987;Ruch and North 1988). According to Reisener (1976), differences among fungal species with respect to the lipid content of dormant spores refl ect the physiological behavior of the spores, and lipid is the chief storage metabolite and substrate during the germination process.…”

Teliospores of smut fungi teliospore walls and the development of ornamentation studied by electron microscopy

“…Entorrhiza is the genus of smut fungi for which the ultrastructure of the mature teliospore wall is most completely documented in literature (Fineran andFineran 1984, 1992 and other publications of these authors). The mature spore wall of E. casparyana is composed of an electron-dense exosporium (layer 2) covered by globose ornaments which are embedded in fibrous material and have an irregularly structured base (layer 1 including zones 2 and 1, the latter called "labyrinth zone" by Fineran and Fineran 1992). Underneath the exosporium lies a more or less electron-transparent striated zone (layer 3, the middle layer), and the endosporium (layer 4).…”

“…The exosporium (L2) of E. scirpicola (Correns) Sacc. and Sydow is internally ornamented (Fineran and Fineran 1992). Spore wall development (Piepenbring et al 1998a: figs.…”

“…However, it is doubtful whether the two are homologous because the striated zone of Entorrhiza teliospores develops underneath the hyphal wall. Fineran andFineran (1984, 1992) did not study the ultrastructure of partition layers in species of Tilletia, and species of Tilletia and Entorrhiza seem to be only very distantly related on the basis of numerous other characteristics . Due to their different thickness, electron density, and structure the middle layers of the genera cited above are considered a product of convergent evolution.…”

Teliospore wall structure in Entorrhiza (Tilletiaceae) and its relationship to taxonomy of the genus

“…The surface ornamentation of spores in the five species has been investigated using techniques of scanning electron microscopy (SEM) (Fineran 1 9 7 8~) . Transmission electron microscopy (TEM) has also been employed to study the ultrastructure of the spore in E. casparyana (Fineran and Fineran 1984). By correlating techniques of thin sectioning and freeze-etching, this work provided the first insight into the structural complexity of the different layers of the wall and of the organization of the protoplast.…”